OPERATING SYSTEM OVERVIEW An operating System (OS) is an intermediary between users and computer hardware. It provides users an environment in which a user can execute programs conveniently and efciently. In technical terms, It is a sotware which manages hardware. An operating System controls the allocation oresources and services such as memory, processors, devices and inormation. Defnition An operating system is a program that acts as an interace between the user and the computer hardware and controls the execution oall !inds oprograms. "ollowing are some oimportant unctions oan operating System. • #emory #anagement • $rocessor #anagement • %evice #anagement • "ile #anagement • Security • &ontrol over system perormance
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#emory management reers to management o $rimary #emory or #ain #emory.
#ain memory is a large array o words or bytes where each word or byte has its own
address.
#ain memory provides a ast storage that can be access directly by the &$. So or
a program to be executed, it must in the main memory. Operating System does the
ollowing activities or memory management.
• *eeps trac!s o primary memory i.e. what part o it are in use by whom, what
part are not in use.
• In multiprogramming, OS decides which process will get memory when and
how much.
• Allocates the memory when the process re+uests it to do so.
• %eallocates the memory when the process no longer needs it or has been
terminated.
Processor Management
In multiprogramming environment, OS decides which process gets the processorwhen and how much time. -his unction is called process scheduling. Operating
System does the ollowing activities or processor management.
• *eeps trac!s o processor and status o process. $rogram responsible or this
tas! is !nown as trafc controller.
• Allocates the processor(&$) to a process.
• %eallocates processor when processor is no longer re+uired.
Device Management
OS manages device communication via their respective drivers. Operating System
does the ollowing activities or device management.
• *eeps trac!s o all devices. $rogram responsible or this tas! is !nown as the
IO controller.
• %ecides which process gets the device when and or how much time.
A /le system is normally organi0ed into directories or easy navigation and usage. -hese directories may contain /les and other directions. Operating System does the
ollowing activities or /le management.
• *eeps trac! o inormation, location, uses, status etc. -he collective acilities
are oten !nown as /le system.
• %ecides who gets the resources.
• Allocates the resources.
• %eallocates the resources.
Ot!er Im"ortant Activities
"ollowing are some o the important activities that Operating System does.
• Sec#rity 1y means o password and similar other techni+ues, preventing
unauthori0ed access to programs and data.
• $ontro over system "er%ormance 2ecording delays between re+uest
or a service and response rom the system.
• &o' acco#nting *eeping trac! o time and resources used by various 3obs
and users.
• Error (etecting ai(s $roduction o dumps, traces, error messages and
other debugging and error detecting aids.
• $oor(ination 'et)een ot!er so%t)ares an( #sers &oordination and
assignment o compilers, interpreters, assemblers and other sotware to the
various users o the computer systems.
TYPES OF OPERATING SYSTEMS
Operating systems are there rom the very /rst computer generation. Operating
systems !eep evolving over the period o time. "ollowing are ew o the important
types o operating system which are most commonly used.
-he users o batch operating system do not interact with the computer directly.
ach user prepares his 3ob on an o4line device li!e punch cards and submits it to
the computer operator. -o speed up processing, 3obs with similar needs are batched
together and run as a group. -hus, the programmers let their programs with the
operator. -he operator then sorts programs into batches with similar re+uirements.
-he problems with 1atch Systems are ollowing.
• 5ac! o interaction between the user and 3ob.
• &$ is oten idle, because the speeds o the mechanical IO devices is slower
than &$.
• %ifcult to provide the desired priority.
Time+s!aring o"erating systems
-ime sharing is a techni+ue which enables many people, located at variousterminals, to use a particular computer system at the same time. -imesharing or
multitas!ing is a logical extension o multiprogramming. $rocessor6s time which is
shared among multiple users simultaneously is termed as timesharing. -he main
di4erence between #ultiprogrammed 1atch Systems and -imeSharing Systems is
that in case o #ultiprogrammed batch systems, ob3ective is to maximi0e processor
use, whereas in -imeSharing Systems ob3ective is to minimi0e response time.
#ultiple 3obs are executed by the &$ by switching between them, but the switches
occur so re+uently. -hus, the user can receives an immediate response. "or
example, in a transaction processing, processor execute each user program in a
short burst or +uantum o computation. -hat is i n users are present, each user canget time +uantum. 7hen the user submits the command, the response time is in
ew seconds at most.
Operating system uses &$ scheduling and multiprogramming to provide each user
with a small portion o a time. &omputer systems that were designed primarily as
batch systems have been modi/ed to timesharing systems.
Advantages o -imesharing operating systems are ollowing
• $rovide advantage o +uic! response.
• Avoids duplication o sotware.
• 2educes &$ idle time.
%isadvantages o -imesharing operating systems are ollowing.
• 8uestion o security and integrity o user programs and data.
• $roblem o data communication.
Distri'#te( o"erating System
%istributed systems use multiple central processors to serve multiple real timeapplication and multiple users. %ata processing 3obs are distributed among the
processors accordingly to which one can perorm each 3ob most efciently.
-he processors communicate with one another through various communication lines
(such as highspeed buses or telephone lines). -hese are reerred as loosely coupled
systems or distributed systems. $rocessors in a distributed system may vary in si0e
and unction. -hese processors are reerred as sites, nodes, computers and so on.
-he advantages o distributed systems are ollowing.
•
7ith resource sharing acility user at one site may be able to use theresources available at another.
• Speedup the exchange o data with one another via electronic mail.
• I one site ails in a distributed system, the remaining sites can potentially
continue operating.
• 1etter service to the customers.
• 2eduction o the load on the host computer.
•
2eduction o delays in data processing.
Net)or, o"erating System
9etwor! Operating System runs on a server and and provides server the capability
to manage data, users, groups, security, applications, and other networ!ing
unctions. -he primary purpose o the networ! operating system is to allow shared
/le and printer access among multiple computers in a networ!, typically a local area
networ! (5A9), a private networ! or to other networ!s. xamples o networ!
operating systems are #icrosot 7indows Server :;;<, #icrosot 7indows Server
:;;=, 9I>, 5inux, #ac OS >, 9ovell 9et7are, and 1S%.
-he advantages o networ! operating systems are ollowing.
• &entrali0ed servers are highly stable.
• Security is server managed.
• pgrades to new technologies and hardwares can be easily integrated into
• It provides users, services to execute the programs in a convenient manner.
"ollowing are ew common services provided by operating systems.
• $rogram execution
• IO operations
• "ile System manipulation
• &ommunication
• rror %etection
• 2esource Allocation
• $rotection
Program e.ec#tion
Operating system handles many !inds o activities rom user programs to system
programs li!e printer spooler, name servers, /le server etc. ach o these activities
is encapsulated as a process.
A process includes the complete execution context (code to execute, data to
manipulate, registers, OS resources in use). "ollowing are the ma3or activities o an
operating system with respect to program management.
• 5oads a program into memory.
• xecutes the program.
• ?andles program6s execution.
• $rovides a mechanism or process synchroni0ation.
• $rovides a mechanism or process communication.
• $rovides a mechanism or deadloc! handling.
I/O O"eration
IO subsystem comprised o IO devices and their corresponding driver sotware.%rivers hides the peculiarities o speci/c hardware devices rom the user as the
device driver !nows the peculiarities o the speci/c device.
Operating System manages the communication between user and device drivers.
"ollowing are the ma3or activities o an operating system with respect to IO
• &ommunication may be implemented by two methods either by Shared
#emory or by #essage $assing.
Error !an(ing
rror can occur anytime and anywhere. rror may occur in &$, in IO devices or in
the memory hardware. "ollowing are the ma3or activities o an operating system
with respect to error handling.
• OS constantly remains aware o possible errors.
• OS ta!es the appropriate action to ensure correct and consistent computing.
Reso#rce Management
In case o multiuser or multitas!ing environment, resources such as main memory,
&$ cycles and /les storage are to be allocated to each user or 3ob. "ollowing are
the ma3or activities o an operating system with respect to resource management.
• OS manages all !ind o resources using schedulers.
• &$ scheduling algorithms are used or better utili0ation o &$.
Protection
&onsidering a computer systems having multiple users the concurrent execution o
multiple processes, then the various processes must be protected rom each
another6s activities.
$rotection reers to mechanism or a way to control the access o programs,processes, or users to the resources de/ned by a computer systems. "ollowing are
the ma3or activities o an operating system with respect to protection.
• OS ensures that all access to system resources is controlled.
• OS ensures that external IO devices are protected rom invalid access
attempts.
• OS provides authentication eature or each user by means o a password.
OPERATING SYSTEM PROPERTIES
"ollowing are ew o very important tas!s that Operating System handles