Chapter 3 Operating Systems
Chapter 3 Operating Systems. 2 Chapter 3 Operating Systems 3.1 The Evolution of Operating Systems 3.2 Operating System Architecture 3.3 Coordinating the.
Dec 22, 2015
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Transcript
Chapter 3
Operating Systems
2
Chapter 3 Operating Systems 31 The Evolution of Operating
Systems 32 Operating System Architecture 33 Coordinating the Machinersquos
Activities 34 Handling Competition Among
Processes 35 Security
3
Some functions of an operating system Control and Oversee operation of
computer Store and retrieve files Schedule programs for execution Execute programsExMicrosoft Linux(By Linus Torvalds)Open
sourcce
4
Evolution of shared computing Single-Processor Systems1048708 Program execution of earlier computers requires significant
preparation of equipments1048708 Mounting placing the punched cards setting the switches
and so on1048708 Each program execution is referred to as a job an isolated
activity1048708 The next user only gains the full control of the computer after
the completion of the current user [sequentially]1048708 Batching processing executes a batch of collected
jobs pending in the job queue(first-in first-out) (FIFO) without further interaction with users
5
Evolution of shared computing Single-Processor Systems1048708 Interactive processing carries on a dialogue with the user1048708 --It involves real-time processing for the machine to interact with its
environment1048708 --Reservation systems word processing computer games1048708 To serve more than one user or job at a time time-sharing technique
divides time into time intervals or time slices each designated to one task1048708
--Time-sharing used in single-user systems is usually called multitasking1048708 --Tradeoffs1048708 The overhead to rapidly shuffle the jobs to gain the illusion of
concurrent execution of several jobs1048708 The time wasted to await the completion of peripheral devices or userrsquos
inputs1048708 Multiprocessor Systems With networks like the Internet many small
machines can flexibly collaborate for computing in contrast to an expensive large central machine [Grid Computing]
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
2
Chapter 3 Operating Systems 31 The Evolution of Operating
Systems 32 Operating System Architecture 33 Coordinating the Machinersquos
Activities 34 Handling Competition Among
Processes 35 Security
3
Some functions of an operating system Control and Oversee operation of
computer Store and retrieve files Schedule programs for execution Execute programsExMicrosoft Linux(By Linus Torvalds)Open
sourcce
4
Evolution of shared computing Single-Processor Systems1048708 Program execution of earlier computers requires significant
preparation of equipments1048708 Mounting placing the punched cards setting the switches
and so on1048708 Each program execution is referred to as a job an isolated
activity1048708 The next user only gains the full control of the computer after
the completion of the current user [sequentially]1048708 Batching processing executes a batch of collected
jobs pending in the job queue(first-in first-out) (FIFO) without further interaction with users
5
Evolution of shared computing Single-Processor Systems1048708 Interactive processing carries on a dialogue with the user1048708 --It involves real-time processing for the machine to interact with its
environment1048708 --Reservation systems word processing computer games1048708 To serve more than one user or job at a time time-sharing technique
divides time into time intervals or time slices each designated to one task1048708
--Time-sharing used in single-user systems is usually called multitasking1048708 --Tradeoffs1048708 The overhead to rapidly shuffle the jobs to gain the illusion of
concurrent execution of several jobs1048708 The time wasted to await the completion of peripheral devices or userrsquos
inputs1048708 Multiprocessor Systems With networks like the Internet many small
machines can flexibly collaborate for computing in contrast to an expensive large central machine [Grid Computing]
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
3
Some functions of an operating system Control and Oversee operation of
computer Store and retrieve files Schedule programs for execution Execute programsExMicrosoft Linux(By Linus Torvalds)Open
sourcce
4
Evolution of shared computing Single-Processor Systems1048708 Program execution of earlier computers requires significant
preparation of equipments1048708 Mounting placing the punched cards setting the switches
and so on1048708 Each program execution is referred to as a job an isolated
activity1048708 The next user only gains the full control of the computer after
the completion of the current user [sequentially]1048708 Batching processing executes a batch of collected
jobs pending in the job queue(first-in first-out) (FIFO) without further interaction with users
5
Evolution of shared computing Single-Processor Systems1048708 Interactive processing carries on a dialogue with the user1048708 --It involves real-time processing for the machine to interact with its
environment1048708 --Reservation systems word processing computer games1048708 To serve more than one user or job at a time time-sharing technique
divides time into time intervals or time slices each designated to one task1048708
--Time-sharing used in single-user systems is usually called multitasking1048708 --Tradeoffs1048708 The overhead to rapidly shuffle the jobs to gain the illusion of
concurrent execution of several jobs1048708 The time wasted to await the completion of peripheral devices or userrsquos
inputs1048708 Multiprocessor Systems With networks like the Internet many small
machines can flexibly collaborate for computing in contrast to an expensive large central machine [Grid Computing]
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
4
Evolution of shared computing Single-Processor Systems1048708 Program execution of earlier computers requires significant
preparation of equipments1048708 Mounting placing the punched cards setting the switches
and so on1048708 Each program execution is referred to as a job an isolated
activity1048708 The next user only gains the full control of the computer after
the completion of the current user [sequentially]1048708 Batching processing executes a batch of collected
jobs pending in the job queue(first-in first-out) (FIFO) without further interaction with users
5
Evolution of shared computing Single-Processor Systems1048708 Interactive processing carries on a dialogue with the user1048708 --It involves real-time processing for the machine to interact with its
environment1048708 --Reservation systems word processing computer games1048708 To serve more than one user or job at a time time-sharing technique
divides time into time intervals or time slices each designated to one task1048708
--Time-sharing used in single-user systems is usually called multitasking1048708 --Tradeoffs1048708 The overhead to rapidly shuffle the jobs to gain the illusion of
concurrent execution of several jobs1048708 The time wasted to await the completion of peripheral devices or userrsquos
inputs1048708 Multiprocessor Systems With networks like the Internet many small
machines can flexibly collaborate for computing in contrast to an expensive large central machine [Grid Computing]
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
5
Evolution of shared computing Single-Processor Systems1048708 Interactive processing carries on a dialogue with the user1048708 --It involves real-time processing for the machine to interact with its
environment1048708 --Reservation systems word processing computer games1048708 To serve more than one user or job at a time time-sharing technique
divides time into time intervals or time slices each designated to one task1048708
--Time-sharing used in single-user systems is usually called multitasking1048708 --Tradeoffs1048708 The overhead to rapidly shuffle the jobs to gain the illusion of
concurrent execution of several jobs1048708 The time wasted to await the completion of peripheral devices or userrsquos
inputs1048708 Multiprocessor Systems With networks like the Internet many small
machines can flexibly collaborate for computing in contrast to an expensive large central machine [Grid Computing]
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
6
Evolution of shared computing Batch processing Job queue Time-sharing
Multi-tasking multiple tasks for a single user
Interactive processing Real-time processing
Scheduling multiprocessor machines
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
7
Figure 31 Batch processing
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
8
Figure 32 Interactive processing
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
9
Types of software Application software
perform specific tasks for users spreadsheets database systems word processing systems program development software games and so forth
System software perform tasks needed by all computer systems Operating system abstracts the underlying hardware for
the rest of software
Utility software performs fundamental activities yet not included in the OS for simplicity1048708Disk formatting file copying
dial-up compression etc
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
10
Figure 33 Software classification
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
11
Components of an operating system Shell portion that communicates with
users Graphical user interface (GUI) pictorially represents
the objects on the screen and accept the commands like mouse-clicking for execution
Textual shells(Borne shell Korn shell C shell TC shell MS-DOS) is light weighted only accepting the commands issued by a keyboard1048708
Window manager is the component to govern the screen layout of GUI
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
12
Components of an operating system Kernel contains components
performing basic required functions File manager--coordinates the use of mass storage
facilitiesIt keeps records of all the files location (directory folder sub-directory path) access permission and history (file descriptor) free available space etc
Device drivers--are installed into the kernel to drive the corresponding peripheral devices using encapsulated activation steps specified for each device
Memory manager Scheduler and dispatcher
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
13
Components of an operating system
Scheduler--According to some priorities or concerns it determines which activities should be considered for execution
Dispatcher--It administrates the allocation of time slices to the activitiesbeing executed
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
14
Figure 34 The shell as an interface between users and the operating system
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
15
File Manager Directory or folder user-created
group or bundle of files Path position of a file in directory
hierarchy File descriptor information needed
to access an open file
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
16
Memory manager Coordinate the machinersquos use of main
memory Total main memory required exceeds
available(Ie 512MB is requires but only 256MB available) it creates the illusion of additional memory space by rotating back and forth of program and data between main memory and mass storage
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
17
Memory manager
Page divide the required space into units called page (a few kilobytes) and store the content of the page in mass storage
Virtual memory illusionary memory space Created by shuffling units of data
called pages between actual main memory space and mass storage
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
18
Getting it started (bootstrapping)
Bootstrap program in read only memory (ROM) Run by the CPU when power is turned
on Transfers operating system from
mass storage to main memory Executes jump to operating system
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
19
Figure 35 The booting process
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
20
BIOS(Basic Inputoutput System)
In addition to bootstrap read only memory (ROM) contains a set of routines for fundamental inputoutput activities
Receive information from keyboard display message on screen
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
21
Processes Program = a static set of directions
--A program can be run multiple times each instanceactivity called a process
Process = the activity of executing a program --Each process has its own process state
recording the current status of the activity Process state = current status of the activity
Snapshot of relevant parts of the machine state Program counter other registers associated main
memory
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
22
Process administration Scheduler
Keeps state of all processes in an process table(in main memory)
It containsmdashassigned memory area priority and readywaiting
Ready if its progress can continue or waiting if it is awaiting some external events to occur and so on
Priority Non-scheduling information memory
pages etc
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
23
Process administration (continued) Dispatcher
Gives one time slice or quantum to a process that is ready Executes a process switch (or context switch) when the
running processrsquos time slice is over A timer circuit counts down the quantum and generates an
interrupt at the end1048708 Such process switch involves updating the snapshot of
the current process restoring the snapshot of the next process and then starting its execution1048708
A program called interrupt handler is run for scheduler to update the process table select the next process hellipEarly termination of quantum is also possible
Interrupt indicates that time slice is over Interrupt handler part of dispatcher
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
24
Figure 36 Time-sharing between process A and process B
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
25
Handling competition for a resource System resources are shared among
processes1048708 --Some non-shareable resources like printers should not be
simultaneously written by more than one process1048708 Using a flag with the status of set(allocated) and
clear(available) there seems to be only one process allowed to write to the very resource
OS checks the flag and to decide set or clear(notecheck and set may require several machine cycle to finish)
Due to process switch two processes may just be aware of the clear flag right before being preempted1048708
During the following quantum they will proceed to write rArrproblem occurs
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
26
Handling competition for a resource Remedies testing and setting the flag must be
completed wo interruption (atomic) Semaphore = a control flag telling if resource is
in use Test and set must be done together for proper
function Critical region = sequence of instructions that
should be executed by only one process at a time Usually protected by a semaphore
Mutual exclusion = requirement for proper implementation of a critical region
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
27
Deadlock Two processes block each other from
continuing Conditions that lead to deadlock
1 Competition for non-sharable resources2 At least two resources are needed by both
processesThe resources are requested on a partial basis
having some while requesting more
3 An allocated resource can not be forcibly retrieved
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
28
Deadlock Deadlock hArrcyclic wait-for graphs in the
process table 1048708 The super-users may kill some processes
for the rest to be finished1048708 Deadlock avoidance schemes try to alter
the first two conditions1048708 To avoid the 2nd condition each process is
required to request all its resources at a time1048708
To prevent the 1st condition non-shareable resources are converted into sharable ones1048708
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
29
Figure 37 A deadlock resulting from competition for nonshareable railroad intersections
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
30
Spooling Postpone requested operation until a
later time Makes a non-shareable resource appear
shareable Technique of deadlock avoidance Printer spooling may be used for processes to
write to their own designated disk space instead of directly to the printerThen OS sends these printouts to the printer in series1048708
Multiple read accesses to a file finely coexist but conflict with any other write access
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
31
Security from outside attacks Most common protection require
user name and password Problem password stealing Problem automated password guessers Counter measures
Always tell user when heshe last logged in Report repeated bad guesses Log the guesser into a captive account to
spy on the guesser
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
32
Security from attacks from within Operating system prevents illegal
access to resources Different memory for different processes Privileged instructions only allowed in
kernel All file access passes through the kernel Other devices can only be accessed
through the kernel
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