CHAP-1 PART-2

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Operating-System Structures

System ComponentsOperating System

Services

System Calls

System Programs

Virtual Machines

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Common System Components

y Process Management

y Main Memory Management

y Secondary-Storage Management

y I/O System Managementy File Management

y Protection System

y Networking

y Command-Interpreter System

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Process Management

y A process is a program in execution. It is a unit of workwithin the system. Program is a passive entity, process is anactive entity.

y Process needs resources to accomplish its task such as CPU,memory, I/O, files etc.

y These recourses are given to process either when it is

created or allocated when it is running.

y The CPU executes instructions of a program one afteranother, until the process completed.

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Process Management(count.)

y The operating system is responsible for the

following activities in connection with process

management.

yCreating and deleting both user and system

processes

yprocess suspension and resumption.

yProvision of mechanisms for:yprocess synchronization

yprocess communication

ydeadlock handling

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Secondary-Storage Managementy

Since main memory (primary storage

) is volatile and too smallto accommodate all data and programs permanently, thecomputer system must provide secondary storage to back upmain memory.

y Most modern computer systems use disks as the principle

on-line storage medium, for both programs and data.y The operating system is responsible for the following

activities in connection with disk management:

y Free space management

y

Storage allocationy Disk scheduling

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I/O System Managementy A

computer has many devices that facilitate user interactionwith computer.

y Different devices has different working method. For thisderivers of specific device are loaded into computer. When

needed these drivers are loaded in to main memory.

y The operating system is responsible for the followingactivities in connection with I/O System Management:

y A general device-driver interface

y Drivers for specific hardware devices

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Command-Interpreter Systemy One of the most important system program for an OS is the

command interpreter. It is the interface between user and

OS.

y Many commands are given to OS by Control statements.

When a new job OS started in Batch system or a user log on

in a time sharing system, a program executes automatically.

This program reads and interprets control statements. This

program is called Control Card Interpreter or Command

Line interpreter.

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Additional Operating System Functions

A

dditional functions exist not for helping the user, but ratherfor ensuring efficient system operations.

Resource allocation allocating resources to multiple users ormultiple jobs running at the same time.

Accounting keep track of and record which users use howmuch and what kinds of computer resources. It helps in making

future decisions for resource allocation

Protection ensuring that all access to system resources iscontrolled.

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System Calls

y System calls provide the interface between a running

program and the operating system.

y Generally available as assembly-language instructions.

y Several languages (such as C,C++) can be used to

write system calls.

y To understand System call, let a program reads a data

from a file and copy it to another file. The first input

that the program will need is the name of two files.

Once the names are specified , the program must open

both files and then copy the required data. All these are

done with the help of System Calls.

y System call can be divided into 5 categories-------

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Process control

y A running program must stop either normally (end) or

abnormally(Abort). On abnormal stop OS must

provide appropriate message.

y

Load and executes system calls are used to bring aprogram into main memory and its execution.

y If we Create a process than its execution is controlled

by its attributes( priority, cpu time , etc). These

attributes are gained byGet process attribute and set

process attribute system calls. To terminate a process

terminate system calls is used.

y Wait system calls is used when a process waits for an

event(user input, busy resource etc.)

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System calls for Device Management

1. Request device , release device

2. Read, write , reposition3. Get device attribute , set device attribute

4. Logically attach or detach device.(distributed system)

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y There are 2 common methods for communication ,MESSAGE PASSING and SHARED MEMORY.

y In message passing IPC is used. Before communicationstarts a path must be established.

y Each computer in a network has a host name and eachprocess has an ID. To know the name of another host andprocess get hostid and get processid system calls areused.

y The other communicator respond by accept connectionsystem call. Both communicator communicates with thehelp ofread message and write message system calls.

y The close connection system call terminates thecoomunication.

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y In shared memory method processes us map memory system

call.

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System Programs

y System programs provide a convenient environment

for program development and execution. The can be

divided into:

y File manipulation

y Status information

y File modification

y Programming language support

y Program loading and execution

y Communications

y Application programs

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File manipulation

y OS provides programs for---

1. Create file

2. Delete file

3. Rename file

4. Copy file

5. Print file

6. List file

7. Manipulating files

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File modification


y Text editors to create and modify filesy Special commands to search contents of files or perform

transformations of the text

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Programming language support


y Compilers,

y assemblers,

y debuggersy Interpreters

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Program loading and execution


y Absolute loaders

yrelocatable loaders

y linkage editors

y Debugging

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Documents

CHAP-1 PART-2