GATE Operating System Book

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Operating System

For

Computer Science

Information Technology

By

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Syllabus Operating System

THE GATE ACADEMY PVT.LTD. H.O.: #74, Keshava Krupa (third Floor), 30th

Cross, 10th

Main, Jayanagar 4th

Block, Bangalore-11

: 080-65700750,[email protected] Copyright reserved. Web: www.thegateacademy.com

Syllabus for Operating System

Processes, Threads, Inter-process communication, Concurrency, Synchronization, Deadlock, CPU

scheduling, Memory management and virtual memory, File systems, I/O systems, Protection and

security.

Analysis of GATE Papers

(Operating System)

Year Percentage of marks Overall Percentage

2013 12.00

8.12

2012 9.33

2011 5.00

2010 7.00

2009 8.00

2008 9.33

2007 9.33

2006 11.33

2005 2.67

2004 7.33

2003 8.00


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Contents Operating System

THE GATE ACADEMY PVT.LTD. H.O.: #74, KeshavaKrupa (third Floor), 30th

Cross, 10th

Main, Jayanagar 4th

Block, Bangalore-11

080 65700750 i f @th t d C i ht d W b th t d P i

C O N T E N T S

Chapters Page No.

1. Introduction to Operating System 1 10

Introduction 1

Evolution of Operating System 2 3

Major Achievements 3 5

Operating System Operations 5 6

Micro Kernel Architecture 6 8

Assignment 9

Answer Keys 10 Explanations 10

2. Process Management 11 45

Process 11

Process vs Program 11

Process State 11

Process Creation 12 13

Process Termination 13 14

Process Scheduling 14

Interprocess Communication, Concurrencyand Synchronization 14 17

The Critical Section Problem 17 19

Bakery Algorithm 19 20

Semaphores 20 23

The Readers and Writers Problem 23 26

Monitors 26 29

Solved Examples 30 33

Assignment 1 34 38

Assignment 2 38 41

Answer Keys 42 Explanations 42 45

3. Threads 46 -52

Thread 46

Life Cycle Of Threads 46 47

Multithreading 47

Process Vs Thread 48

User Level and Kernel Level Threads 48 50

Assignment 50 51

Answer Keys 52 Explanations 52


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4. CPU Scheduling 53 77

Basic Concept 53

Schedulers 53

54 Scheduling Methodology 54

CPU Scheduling Algorithm 54 62


Assignment 1 68 72

Assignment 2 72 73

Answer Keys 74

Explanations 74 77

5. Deadlocks 78 -92

Definition 78 Resource Allocation Graph 78

Condition for Deadlock 78 79

Deadlock Prevention 79

Deadlock Avoidance 79 82

Deadlock Detection 82 83

Recovery From Deadlock 84

Assignment 1 85 88

Assignment 2 88 89

Answer Keys 90

Explanations 90

92

6. Memory Management 93-134

Introduction 93

Logical and Physical Address Space 93 94

Memory Management Requirements 94 96

Memory Allocation Method 96 102

Paging 102 106

Segmentation 106 109

Page Replacement Algorithm 110 112

Thrashing 112

113


Assignment 1 126 128


Answer Keys 130

Explanations 130 134

7. File System 135 153

Introdution 135

File Concept 135 137

Access Methods 137

138


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Directory Structure 138 140

Protection 140 144

Free Space Management 144

145 Solved Examples 146 147



Answer Keys 152

Explanation 152 153

8. I/O System 154 - 172

Kernel I/O Subsystem 154

Disk Structure 154 155

Disk Scheduling 155

157 Disk Management 157 158

RAID 158 159




Answer Keys 169


9. Protection and Security 173 185

Domain of Protection 173

Access Matrix 173 176

The Security Problem 176 178




Answer Keys 184


Module Test 186 199

Test Questions 186 194

Answer Keys 195


Reference Books 200


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Chapter 1 Operating System


Cross, 10th

Main, Jayanagar 4th

Block, Bangalore-11

080 65700750 i f @th t d C i ht d W b th t d P 1

CHAPTER 1

Introduction to Operating System

What is an Operating System?

An operating system is a collection of programs and utilities. It act as the interface between user

and computer. It creates a user friendly environment. The Operating System act as a ResourceManager. (A Computer system has many resources (Hardware and Software) which may require

for completing a task). The computer uses resources like input/output device, memory, file,

storage space, CPU time and so on. The operating system acts as a manager of these resourcesand allocates them to specific program and users as necessary for their tasks. Therefore we cansay an operating system act as a resource manager. Generally resource sharing in two ways in

time and in space. For example a CPU is a time sharing resource and the main memory is a

space sharing resource. The main difference between in time sharing and in space sharingresource is in time resource is not divided into units, where as in space resources is divided

into units.

Structure of Operating System

The structure of operating system consists of 4 layers; these are hardware, software, systemprogram and application program. The hardware part consists of CPU, main memory, I/O device,Secondary storage etc. The software includes process management routines, memory

management routines, I/O control routines, file management routines. The system programlayer consist of complier, assembler etc. Last one is the application program that depends on

users.

Components of a Computer System


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Evolution of Operating System

i.

Serial Processing:Before 1950 the programmer directly interacts with hardware. Therewas no operating system at that time, if the programmer wish to execute a program onthese days, the following steps are necessary.

Type the program on punch card

Convert punched card to card reader

Submit to the computing machine, is there any error, the condition was indicatedby lights.

The programmer examines the registers and main memory to identify the cause of

error.

Take the output of error.

Take the output on the printers.

Then the programmer ready for the next program

This type of processing takes much time and next program should wait for the completion of

previous one. The programs are submitted to the machine one after one. Therefore this

machine is said to be serial processing.

ii. Batch Processing:In older days (before 1960), it was difficult to execute a program usingcomputer. Because the computer located in three rooms. One room for card reader

second room for executing the program third room for printing the result. The user ormachine operator needs to run between these three rooms to complete a job. We can

solve this problem using Batch processing. In batch processing same type of task aregrouped together and execute at a time. The carrier carries the group of job at a time

from one room to another. Therefore the programmer need not to run between these 3rooms several times.

iii. Multiprogramming: Multiprogramming is a technique to execute number of programs

simultaneously by a single processor. In multiprogramming more than one process canreside in main memory at a time. The operating system picks and begins execute one of

the jobs in the main memory.

In non multiprogramming system, the CPU can execute only one program at a time. If therunning program is waiting for any I/O device, the CPU becomes idle, so it will effect the

performance of the CPU. But in multiprocessing environment, any I/O wait happened ina process and then the CPU switches from the job to another job in the job pool. So the

CPU is not idle at any time.

iv. Time Sharing System: Time sharing or multitasking is a logical extension ofmultiprocessing. In time sharing system the CPU selects a job from the ready queue and

switches the CPU to that job. When the time slot is expired the CPU switches from thisjob to another, in this method CPU is shared by different process, so it is said to be Time

Sharing System. The main advantage of time sharing system over the batch processingsystem is the user can interact with the job when it is executing but it is not possible in

batch system. Another advantage of time sharing system is efficient CPU utilization.

v. Parallel System: If a system has more than one processor in close communication,

sharing the computer bus, the clock, memory and peripheral devices, this system is

referred as tightly coupled system. A system consisting of more than one processor andif it is a tightly coupled and then the system is called parallel system. One advantage of


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parallel system is increased Throughpu

t. The performance of CPU is measured in terms

of Throughput. The number of jobs completed by a CPU with in a time period is said to be

hrou hput.

Multiprocessor can also save money compared to multiple single system because the

processor can share peripherals, cabinet and power supply. Another advantages ofmultiprocessor system is that they increase reliability.

vi. Distributed System: In distributed system, the processor cant share memory or clock,each processor has its own local memory. The processor communicate one another

though various communication lines. These system are usually called loosely coupled

system. The advantage of distributed system are:

1. Resource sharing2.

Computation speed up

3.

Reliability

vii. Real Time System

Used when there are rigid time requirements on the operating of a processor or the

flow of data.

Systems that control scientific experiments, medical imaging systems, industrial

control systems and some display system are real time systems.

Two types of real time systems are:

A hard real time system:guarantees that critical tasks completed on time. Soft real time system:A less restrictive type of real time system is a soft real

time system. Given their date of deadline support they are risky to use forindustrial control and robotics

Spooling

The expansion of spooling is simultaneous peripheral operations on line. Simultaneous

means for example if two or more user issue print command and the printer accept the

request even the printer is printing some other jobs. The printer printing one job at the

same time the spool disk can load some other jobs.

Operating System Functions

1.

Program creation

2. Programs execution3. Input output operation

4. Error detection

5.

Resource allocation6.

Accounting

7. Protection

Major Achievements

The major achievement of operating system are

Process Management

A process is a program in execution: (A program is passive in nature while a process is active)

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


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Management of Processes Includes:

Process scheduling (priority, time management,)

Creation/termination

Block/Unblock (suspension/resumption)

Synchronization

Communication

Deadlock handling

Debugging

Main Memory Management

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

Maintenance of several processes at a time Keep track of whos using what memory

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

program (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 (non volatile) storage media

I O Management

Buffer caching system

Generic device driver code

Drivers for each device- translate requests into position commands

Secondary Storage Management

Disk, tapes, optical

Free space management ( paging/swapping)

Storage allocation (what data goes where on disk)

Disk scheduling

Networking

Communication system between distributed processors. Getting information about files/processes/etc. on remote machine.


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

Protection

Of files, memory, CPU, etc.

Means controlling of access

Depends on the attributes of the file and user

System Program

Command Interpreters Program that accepts control statements (shell, GUI interface,etc.)

Compilers/linkers

Communication (ftp, telnet, etc.)

System Tailoring

Modifying the operating System program for a particular machine. The goal is to include all thenecessary pieces but not too many extra ones.

Typically a System can support many possible devices but any one installation has only afew of these possibilities.

Plug and play allows for detection of device and automatic inclusion of the code (driver)necessary to drive these devices.

A system is usually a link of many OS routines/modules in order to produce anexecutable code to run the drivers.

Operating System Operations

Modern operating systems are interrupt driven. If there are no processes to execute, no I/O

devices to service and no users to respond, an operating system will quietly waiting forsomething to happen. Events are almost always signaled by the occurrence of an interrupt or a

trap.

Traps and interrupts

are events that disrupt the normal sequence of instruction executed by the

CPU. A trap is an abnormal condition detected by the CPU, that usually is an indicative of anerror.

Trap condition can occur in following ways(a)

Dividing by zero(b)

Trying to access a memory location that does not exists or for which the program does

not have access(c) Executing an instruction with an undefined opcode,

(d)

Trying to access a nonexistent I/O device.

An nt rrupt is a signal sent to the CPU by an external device, typically an I/O device. It is theCPUs equivalent of a pager, a signal requesting the CPU to interrupt its current activities to

attend to the interrupting device needs. A CPU will check interrupts only after it has completedthe processing of one instruction and before it fetches a subsequent one.

The CPU responds to traps and interrupts by saving the current value of the program counterand resetting the program counter to a new address. This allows the CPU to return to the

executing point where the trap or interrupt occurred, after it has executed a procedure for

handling the trap or interrupt.


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GATE Operating System Book