Section02 Structures

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Jerry Breecher

OPERATING SYSTEMS

STRUCTURES


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What Is In This Chapter?

System Components

System Calls

How Components Fit Together

Virtual Machine

OPERATING SYSTEM

Structures


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OPERATING SYSTEM

STRUCTURES

These are the pieces of the system well be looking at:

Process Management

Main Memory Management

File ManagementI/O System Management

Secondary Management

Networking

Protection System

Command-Interpreter System

SYSTEM

COMPONENTS


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OPERATING SYSTEM

STRUCTURES

PROCESS MANAGEMENT

A process is a program in execution: (A program is passive, a process active.)

A process has resources (CPU time, files) and attributes that must be managed.

Management of processes includes:

y Process Scheduling (priority, time management, . . . )

y Creation/termination

y

Block/Unblock (suspension/resumption )y Synchronization

y Communication

y Deadlock handling

y Debugging

SYSTEM

COMPONENTS


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MAIN MEMORY MANAGEMENT

y Allocation/de-allocation for processes, files, I/O.

y Maintenance of several processes at a time

y Keep track of who's using what memory

y Movement of process memory to/from secondary storage.

FILE MANAGEMENT

A file is a collection of related information defined by its creator. Commonly, files

represent programs (both source and object forms) and data.

The operating system is responsible for the following activities in connections with file

management:

File creation and deletion.

Directory creation and deletion.

Support of primitives for manipulating files and directories.

Mapping files onto secondary storage.

File backup on stable (nonvolatile) storage media.

OPERATING SYSTEM

STRUCTURESSystem

Components


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I/O MANAGEMENT

y Buffer caching system

y Generic device driver code

y Drivers for each device - translate read/write requests into disk position

commands.

SECONDARY STORAGE MANAGEMENTy Disks, tapes, optical, ...

y Free space management ( paging/swapping )

y

Storage allocation ( what data goes where on disk )

y Disk scheduling

OPERATING SYSTEM

STRUCTURESSystem

Components


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NETWORKING

y Communication system between distributed processors.

y Getting information about files/processes/etc. on a remote machine.

y Can use either a message passing or a shared memory model.

PROTECTION

y Of files, memory, CPU, etc.

y Means controlling of access

y Depends on the attributes of the file and user

SYSTEM PROGRAMSy Command Interpreters -- Program that accepts control statements

(shell, GUI interface, etc.)

y Compilers/linkers

y Communications (ftp, telnet, etc.)

OPERATING SYSTEM

STRUCTURESSystem

Components

How Do These All FitTogether?

In essence, they all provide

services for each other.


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Modifying the Operating System program for a particular machine. The goal is to include

all the necessary pieces, but not too many extra ones.

y Typically a System can support many possible devices, but any one installation has

only a few of these possibilities.

y Plug and play allows for detection of devices and automatic inclusion of the code

(drivers) necessary to drive these devices.

y A sysgen is usually a link of many OS routines/modules in order to produce an

executable containing the code to run the drivers.

OPERATING SYSTEM

STRUCTURESSystem

Tailoring


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ASystem Call is the main way a user program interacts with the Operating System.

code forsystem

call 13

operating system

user program

use parametersfrom table X

register

X

X: parameters

for call

load address X

system call 13

Figure 3.1

Figure 2.8

OPERATING SYSTEM

STRUCTURESSystem Calls

Check out the Linux system command strace!


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HOW A SYSTEM CALL WORKS

yObtain access to system space

yDo parameter validation

ySystem resource collection ( locks on

structures )yAsk device/system for requested item

ySuspend waiting for device

yInterrupt makes this thread ready to run

yWrap-up

yReturn to user

There are 11 (or more) steps in making the system call

read (fd, buffer, nbytes)

OPERATING SYSTEM


LinuxAPI


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Consider the ReadFile() function in the

Win32APIa function for reading from a file.

A description of the parameters passed to ReadFile()

HANDLE filethe file to be read

LPVOID buffera buffer where the data will be read into and written from

DWORD bytesToReadthe number of bytes to be read into the buffer

LPDWORD bytesReadthe number of bytes read during the last read

LPOVERLAPPED ovlindicates if overlapped I/O is being used

OPERATING SYSTEM


Example of Windows API


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OPERATING SYSTEM


Msg Passing Shared Memory

Two ways of passing

data between programs.


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OPERATING SYSTEM


These are examples

of various system

calls.


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A SIMPLE STRUCTURE:

Example of MS-DOS.

Application Programming

Resident System Programming

MS-DOS Drivers

ROM - BIOS Device Drivers

Note how all

layers can touch

the hardware.

Bad News!!

OPERATING SYSTEM

STRUCTURESHow An Operating

System Is Put

Together


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A LAYERED STRUCTURE:

Example of Windows 2000.

System Services

Windows

MGR

& GDI

Windows 2000 Kernel

Hardware Abstraction Layer (HAL)

IO

ManagerGraphicsDevice

Drivers

VM

Manager

Security

Reference

Monitor

Process

Manager

OPERATING SYSTEM


System Is Put

Together


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A LAYERED STRUCTURE:

Example ofUNIX.

OPERATING SYSTEM


System Is Put

Together


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In a Virtual Machine - each process "seems" to execute on its own processor with its own

memory, devices, etc.

y The resources of the physical machine are shared. Virtual devices are sliced out of the

physical ones. Virtual disks are subsets of physical ones.

y Useful for running different OS simultaneously on the same machine.

y Protection is excellent, but no sharing possible.

y Virtual privileged instructions are trapped.

Virtual User

Virtual Machine

Monitor Mode

Physical User

Physical Machine

OPERATING SYSTEM

STRUCTURESVirtual Machine


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OPERATING SYSTEM



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Example of MS-DOS on top of Windows XP.

DOS APPLICATION

BIOS DRIVERS

Windows XP

Physical User

Physical Machine

OPERATING SYSTEM



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Example of Java Virtual Machine

The Java Virtual Machine

allows Java code to be portable

between various hardware and

OS platforms.

OPERATING SYSTEM



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OPERATING SYSTEM STRUCTURES

WRAPUP

Weve completed our second overview of an Operating System this atthe level of a high flying plane.

Weve looked at the basic building blocks of an operating system processes, memory management, file systems, and seen how they allconnect together.

Now well get into the nitty-gritty, spending considerable time on each ofthese pieces.

Section02 Structures

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