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SEC CSE/IV OS LAB MANUAL

1

SRINIVASAN ENGINEERING COLLEGE

COMPUTER SCIENCE AND ENGINEERING

ANNA UNIVERSITY OF TECHNOLOGY TRICHIRAPALLI

REGULATION 2009

II CSE (2011-2015)

CS2257

OPERATING SYSTEM LAB

LAB MANUAL

BY

VEENA ALPHONSA JOSE, Assistant Professor.


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Preface

This laboratory manual is prepared by the Department of Computer Science and engineering

for Operating system Laboratory (CS-2257). This lab manual can be used as instructional book for

students, staff and instructors to assist in performing and understanding the experiments. In the first

part of the manual, experiments as per syllabus are described and in the second part of the manual,

experiments that are beyond the syllabus but expected for university laboratory examination are

displayed. This manual will be available in electronic form from Colleges official website, for the

betterment of students.

Acknowledgement

We would like to express our profound gratitude and deep regards to the support offered by

the Chairman Shri. A.Srinivasan. We also take this opportunity to express a deep sense of

gratitude to our Principal Dr.B.Karthikeyan,M.E,Ph.D, for his valuable information and

guidance, which helped us in completing this task through various stages. We extend our hearty

thanks to our head of the department Asst Prof.P.Jayanthi M.E, for her constant encouragement

and constructive comments.

Finally the valuable comments from fellow faculty and assistance provided by thedepartment are highly acknowledged.


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TABLE OF CONTENTS

CHAPTER NO TOPIC PAGE NO

I

Introduction to the languageMain Features

Advantages

Limitations

Applications

4

II Syllabus 6

III System Requirements 7

IV

Description about each experiment

Aim

Learning ObjectiveGeneral procedure to executeprograms

8

V Experiments

1 Write programs using the following system calls of UNIXoperating system: fork, exec, getpid, exit, wait, close, stat,opendir, readdir.

10

2 Write programs using the I/O system calls of UNIXoperating system (open, read, write, etc)

16

3 Write C programs to simulate UNIX commands like ls, grep,

etc.20

4 Given the list of processes, their CPU burst times and arrivaltimes, display/print the Gantt chart for FCFS and SJF. Foreach of the scheduling policies, compute and print theaverage waiting time and average turnaround time. (2sessions)

24

5 Given the list of processes, their CPU burst times and arrivaltimes, display/print the Gantt chart for Priority and Roundrobin. For each of the scheduling policies, compute and printthe average waiting time and average turnaround time. (2sessions).

32

6 Developing Application using Inter Process Communication(using shared memory, or message queues)

40

7 Implement the Producer Consumer problem usingsemaphores (using UNIX system calls)

46

8 Implement some memory management schemes I 50

9 Implement some memory management schemes II 58

10 Implement any file allocation technique (Linked,Indexed or Contiguous)

63


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INTRODUCTION OF THE LANGUAGE (Linux)

MAIN FEATURES

Linux is a generic term referring to Unix-like computer operating systems based on the

Linux kernel. Their development is one of the most prominent examples of free and open sourcesoftware collaboration; typically all the underlying source code can be used, freely modified, and

redistributed by anyone. The name "Linux" comes from the Linux kernel, originally written in

1991 by Linus Torvalds. The rest of the system usually comprises components such as the Apache

HTTP Server, the X Window System, the K Desktop Environment, and utilities and libraries from

the GNU operating system (announced in 1983 by Richard Stallman). Many quantitative studies of

free / open source software focus on topics including market share and reliability, with numerous

studies specifically examining Linux. The Linux market is growing rapidly, and the revenue of

servers, desktops, and packaged software running Linux was expected to exceed $35.7 billion by

2008.

ADVANTAGES

Cost The most obvious advantage of using Linux is the fact that it is free to obtain, while

Microsoft products are available for a hefty and sometimes recurring fee.

Security In line with the costs, the security aspect of Linux is much stronger than that of

Windows.

Choice (Freedom) The power of choice is a great Linux advantage. With Linux, you

have the power to control just about every aspect of the operating system.

Software - There are so many software choices when it comes to doing any specific task.

You could search for a text editor on Freshmeat and yield hundreds, if not thousands of

results. My article on 5 Linux text editors you should know about explains how there are so

many options just for editing text on the command-line due to the open source nature

of Linux.

Hardware - Linux is perfect for those old computers with barely anyprocessing power or

memory you have sitting in your garage or basementcollecting dust .

LIMITATIONS

Understanding Becoming familiar with the Linux operating system requires patience as

well as a strong learning curve. You must have the desire to read and figure things out on

your own, rather than having everything done for you. Check out the 20 must read howtos

and guides for Linux.

Compatibility Because of its free nature, Linux is sometimes behind the curve when it

comes to brand new hardware compatibility. Though the kernel contributors and
http://www.freshmeat.net/


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maintainers work hard at keeping the kernel up to date, Linux does not have as much of a

corporate backing as alternative operating systems. Sometimes you can find third party

applications, sometimes you cant.

Alternative Programs Though Linux developers have done a great job at creating

alternatives to popular Windows applications, there are still some applications that exist on

Windows that have no equivalent Linux application. Read Alternatives to Windows

Applications to find out some of the popular alternatives.

APPLICATIONS

1. OpenShot (Video editor)

2. Apache (Web server)

3. Firefox (Web browser)

4. Dropbox (Online storage)

5. Asterisk (Telephony)


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HARDWARE REQUIREMENTS

System : 1

O/S : Linux or Unix

Compiler : Turbo C or TC3


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ABOUT THE OPERATING SYSTEM LAB

AIM

At the end of the course students should be able to

describe the general structure and purpose of an operating system;

explain the concepts of process, address space, and file; compare and contrast various CPU scheduling algorithms;

understand the differences between segmented and paged memories, and be able todescribe the advantages and disadvantages of each;

Compare and contrast polled, interrupt-driven and DMA-based access to I/O devices..

OVERVIEW OF THE EXPERIMENTS

To implement various page replacement memory management schemes to compare and

contrast the relative performance of different page replacement schemes.

Inter Process Communication Using Shared Memory and Message Queuescan

communicates among them using the Shared Memory regions. Shared Memory is an

efficient means of passing data between programs. One program will create a memory

portion, which other processes (if permitted) can access. A shared segment can be attached

multiple times by the same process

The way to use the most common system calls in order to make input-output operations on

files, as well as operations to handle files and directories in the Linux operating system.

Implementation of FCFS and SJF Scheduling, This selects each process from the processes

in memory that are ready to execute, and allocates the CPU to one of them using First In

First Out and Shortest Job First Scheduling .

LEARNING OBJECTIVES.

The objective of this lab is to teach students about various operating systems including

Windows, Mac and Unix. Students learn about systems configuration and administration. Students

learn, explore and practice technologies related to mobile computing.


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.

GENERAL PROCEDURE FOR EXECUTING PROGRAMS

1. Use the pico editor to create a file called hello.c containing the following lines:

#include

int main() {

printf("Hello World\n");

}

2. Save this file. At the UNIX command prompt, invoke the gcc compiler as follows:

gcc hello.c

3. The result of this step (provided there are no syntax errors in the program) will be an

Executable file called a.out. This is the default file name given by the compiler

4. To execute the program type: ./a.out

The period and slash in front of the a.out indicate to run the a.out file in the currentdirectory

5. To compile a program and save the compiled version in a different file name, use the

-o option as in: gcc -o hello.exe hello.c

6. Note: To avoid having to put the ./ in front of the file name to execute a program, you mayadd the current directory (indicated by a period) in your PATH by typing: PATH=$PATH:.

Note the final two characters are a full colon followed by a period


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EX.NO:1

DATE:

IMPLEMENTATION OF SYSTEM CALLS

DESCRIPTION

Thefork() function shall create a new process. The new process (child process) shall be anexact copy of the calling process (parent process). The child process shall have a unique

process ID.

The exec family of functions shall replace the current process image with a new processimage. The new image shall be constructed from regular, executable file called the new

process image file

The exit status will be n, if specified. Otherwise, the value will be the exit value of the lastcommand executed, or zero if no command was executed. When exitis executed in a trapaction, the last command is considered to be the command that executed immediately

preceding the trap action

The readdir() function returns a pointer to a dirent structure representing the next directoryentry in the directory stream pointed to by dir.

The opendir() function opens a directory stream corresponding to the directory name, andreturns a pointer to the directory stream. The stream is positioned at the first entry in the

directory

OBJECTIVE

To keep track of how many times each of the fork, vfork, execl, readdir, opendir and waitsystem

calls is invoked

Place counters in kernel code

Implement a new system call providing this information

Request/retrieve these values from user space by invoking the new system call/s

SYNTAXES & KEYWORDS

Fork:

#include

pid_t fork(void);

execl:

#include


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extern char **environ;

int execl(const char *path, const char *arg(), /*, (char *)0 */);

exit:

#include

void exit(int status);

wait:

#include

#include

pid_t wait(int *stat_loc);

Readdir() :

#include

#include

struct dirent *readdir(DIR *dir);

Opendir():

#include #include

DIR *opendir(const char *name);

HOW TO EXECUTE THE PROGRAM

Creates New child process

Gets the process id

Waits until the process resumes

Exits the program

ADVANTAGE

Each device can be accessed as though it was a file in the file system. Since most of the kernel

deals with devices through this file interface, it is relatively easy to add a new device driver by

implementing the hardware-specific code to support this abstract file interface. Therefore, this

benefits the development of both user program code, which can be written to access devices and

files in the same manner, and device driver code, which can be written to support a well-defined

API.


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Program inodeno:1815607

Program Size :4096

Access Time :Thu Mar 30 11:45:06 2006

Modified Time :Tue Mar 7 10:31:36 2006Protection :33204

User id :514

Group id :514

Device driverno:769

No. of links :1

c) opendir & readdir

//ls command implementation using opendir & readdir //ls command implementation

#include

#include main(int argc,char *argv[])

{

DIR * dir;struct dirent *direntry; dir=opendir(argv[1]); while((direntry=readdir(dir))!=NULL)

printf("%d %s\n",direntry->d_ino,direntry->d_name); closedir(dir);

}

OUTPUT:

[cse04@LINUXSERVER vaishu]$ cc ordir.c

[cse04@LINUXSERVER vaishu]$ ./a.out uma

1750301 .

3270767 ..

1750302 aaa

RESULT

The program for process system call has been executed and shown the result as above.

VIVA QUESTIONS

1. What is an Operating system?

An operating system is a program that manages the computer hardware. It also provides a

basis for application programs and act as an intermediary between a user of a computer and the

computer hardware. It controls and coordinates the use of the hardware among the various


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application programs for the various users.

2. What is the use of fork and exec system calls?

Fork is a system call by which a new process is created. Exec is also a system call, which is

used after a fork by one of the two processes to replace the process memory space with a new

program.

POSSILBLE QUESTIONS

1. Write programs using the following system calls of UNIX operating system: fork, exec, getpid, exit, wait,close, stat, opendir, readdir.

2. Write programs using getpid, exit, wait system calls.


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EX.NO:2

DATE:

IMPLEMENTATION OF I/O SYSTEM CALL

DESCRIPTION

File-I/O through system calls is simpler and operates at a lower level than making calls to the C

file-I/O library. There are seven fundamental file-I/O system calls:

creat() Create a file for reading or writing.

open() Open a file for reading or writing.

close() Close a file after reading or writing.

write() Write bytes to file.

read() Read bytes from file.

These calls were devised for the UNIX operating system and are not part of the ANSI C spec. Use

of these system calls requires a header file named "fcntl.h":

SYNTAXES & KEYWORDS

open() :

= open( , );

write() :

write( , , );

read() :

read( , , );

HOW TO EXECUTE THE PROGRAM

Creates a new file

Opens an existing fie

Closes a file that is open

Reads a file

Writes the bytes of data into a file


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ADVANTAGE

Each device can be accessed as though it was a file in the file system. Since most of the

kernel deals with devices through this file interface, it is relatively easy to add a new device driver

by implementing the hardware-specific code to support this abstract file interface. Therefore, this

benefits the development of both user program code, which can be written to access devices and

files in the same manner, and device driver code, which can be written to support a well-defined

API.

DISADVANTAGE

The disadvantage with using the same interface is that it might be difficult to capture the

functionality of certain devices within the context of the file access API, thereby either resulting in

a loss of functionality or a loss of performance. Some of this could be overcome by the use of ioctloperation that provides a general purpose interface for processes to invoke operations on devices.

APPLICATIONS

System calls acts as entry point to OS kernel. There are certain tasks that can only be done

if a process is running in kernel mode. Examples of these tasks can be interacting with hardware

etc. So if a process wants to do such kind of task then it would require itself to be running in kernel

mode which is made possible by system calls.

ALGORITHM:

1. Start the Program.

2. Open a file for O_RDWR for read and write, O_CREATE for creating a file, O_TRUNC

for truncates a file.

3. Using getchar function, read the character and stored in the string [] array.

4. The string [] array is write into a file and close it.

5. Then the file is opened for read only mode and read the characters and displayed it and

close the file.

6. Stop the program.

PROGRAM

#include

#include

#include


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#include int main()

{

int n,i=0; int f1,f2;

char c,strin[100]; f1=open("data",O_RDWR|O_CREAT|O_TRUNC); while((c=getchar())!='\n')

{

strin[i++]=c;

}

strin[i]='\0';

write(f1,strin,i);

close(f1); f2=open("data",O_RDONLY); read(f2,strin,0);

printf("\n%s\n",strin); close(f2);

return 0;

}

OUTPUT:

[cs2002@localhost ~]$ cc isc.c

[cs2002@localhost ~]$ ./a.out HAI

WELCOME TO CSEHAI WELCOME TO CSE [cs2002@localhost ~]$

RESULT

The i/o system call program has been executed and shown the results as above.

VIVA QUESTIONS

1. What is a process?

A process is a program in execution. It is the unit of work in a modern operating system. A

process is an active entity with a program counter specifying the next instructions to execute and a

set of associated resources. It also includes the process stack, containing temporary data and a data

section containing global variables.

2. What is a process state and mention the various states of a process?

As a process executes, it changes state. The state of a process is defined in part by the

current activity of that process. Each process may be in one of the following states: New

Running


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Waiting

Ready

Terminated

POSSILBLE QUESTIONS:

1. Write programs using the I/O system calls of UNIX operating system (open, read, write,

etc)

2. Write programs using the I/O system call(write).

\


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EX.NO:3

DATE:

SIMULATION OF UNIX COMMANDS

DESCRIPTION

ls -a

The -a option tells the ls command to report information about all files, including hidden files.

ls -l

The -l option tells the "ls" command to provide a longlisting of information about the files anddirectories it reports. The long listing will provide important information about file permissions,user and group ownership, file size, and creation date

ls -al

This command provides a long listing of information about all files in the current directory. It

combines the functionality of the -a and -l options. This is probably the most used version of the ls

command.

ls -alR /usr | more

This command lists long information about all files in the "/usr" directory, and all sub-directories

of /usr. The -R option tells the ls command to provide a recursive listing of all files and sub-

directories

ls -ld /usr

Rather than list the files contained in the /usr directory, this command lists information about the

/usr directory itself (without generating a listing of the contents of /usr). This is very useful when

you want to check the permissions of the directory, and not the files the directory contains.

SYNTAXES & KEYWORDS

ls Command:

ls [options] [names]

grep Command:

grep flag PatternList filename

EXPECTED OUTPUT AND ITS FORM

List the files in the directory.

List the files of a particular user in a directory.

List the files with its description.


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Searches the patterns in a file

ADVANTAGES

Full multitasking with protected memory.

Multiple users can run multiple programs each at the same time.

Very efficient virtual memory, so many programs can run with a modest amount of

physical memory.

Access controls and security

A rich set of small commands and utilities that do specific tasks well

DISADVANTAGES

The traditional command line shell interface is user hostile -- designed for the

programmer, not the casual user.

Commands often have cryptic names and give very little response to tell the user what

they are doing.

APPLICATIONS

Commands you use in a Unix based computer OS to achieve certain things. Similar to MS/DOS

commands in Windows. Mostly used in computers running the Linux OS.

ALGORITHM:

1. Start the program.

2. Enter the options.

3. If the option is 1call ls command and it display the files.

4. If the option is 2 call gerp command and match the given pattern with the read word and

if it matches, display the line of occurance.

5. If the option is 3 call cp command.6. If the option is 4 call rm command.


PROGRAM

#include

main()

{

char c; int n;
http://wiki.answers.com/Q/What_are_the_advantages_and_disadvantages_of_Unixhttp://wiki.answers.com/Q/What_are_the_advantages_and_disadvantages_of_Unix


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printf("1.list of files in the directory\n2.list the lines\n3.copy\n4.remove\n"); scanf("%d",&n);

switch(n)

{

case 1: system("ls"); break;

case 2:

system("grep argc lsgp.c"); break;

case 3:

system(" cp lsgp.c gpls.c"); printf("the file is

copied"); break;

case 4:

system("rm lsgp.c"); printf("the file is deleted");

break;

}

}

OUTPUT

[it53@localhost ~]$ cc lsgp.c [it53@localhost ~]$

./a.out 1.list of files in the directory 2.list the lines3.copy

4.remove

1

3q bit.c ftp.c ospf1.c praba.c rarp.c smp.c sort.sh

a.out forkexec.c io.c praba1.sh praba.sh sample sorting.sh syscall.c [it53@localhost ~]$ ./a.out

1.list of files in the directory 2.list the lines

3.copy4.remove

2

system("grep argc lsgp.c"); [it53@localhost ~]$

./a.out 1.list of files in the directory 2.list the lines

3.copy

4.remove

3the file is copied[it53@localhost ~]$ ./a.out 1.list of files in the


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directory

2.list the lines 3.copy 4.remove

4

the file is deleted

RESULT

The program for simulation of unix commands ls and grep has been executed and the shownthe results as above

VIVA QUESTIONS:

1. Compare user threads and kernel threads.

User threads

User threads are supported above the Kernel threads are supported directly kernel and are

implemented by a thread library at the user level Thread creation & scheduling are done in the user

space, without kernel intervention. Therefore they are fast to create and manage Blocking system

call will cause the entire process to block

Kernel threads

Thread creation, scheduling and management are done by the operating If the thread

performs a blocking system call, the kernel can schedule another thread in the application for

execution.

2. How can a user program disrupt the normal operations of a system?

A user program may disrupt the normal operation of a system by Issuing illegal I/O operations By

accessing memory locations within the OS itself Refusing to relinquish the CPU

POSSIBLE QUESTIONS:

1. Write C programs to simulate UNIX commands like ls, grep, etc

2. Write C programs to simulate UNIX commands like grep


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EX.NO:4(a)

DATE:

IMPLEMENTATION OF FCFS SCHEDULING

DESCRIPTION

The FCFS scheduler simply executes processes to completion in the order they are submitted.This code implements the First come First Served Scheduled algorithm. It gets the number of

processes and the process name, burst time and arrival time for each user from the user. It thensorts the processes depending upon the arrival time. Calculates and displays the averageturnaround time and waiting time. Then it will display the Gantt chart.


Performs FCFS scheduling ie) the process that enters the queue first is served first.

ADVANTAGES

simple

easy to understand firstcome, first served

DISADVANTAGES

This scheduling method is nonpreemptive, that is, the process will run until it finishes.

Because of this nonpreemptive scheduling, short processes which are at the back of thequeue have to wait for the long process at the front to finish

ALGORITHM:


2. Get the number of processes and their burst time.

3. Initialize the waiting time for process 1 is 0.

4. The waiting time and turn around time for other processes are calculated as

p[i].wt=p[i-1].bt+p[i-1].wt;

p[i].tt=p[i].bt+p[i].wt;

5. The waiting time and turn around time for all the processes are summed and then the

average waiting time and turn around time are calculated.

6. The average waiting time and turn around time are displayed.



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PROGRAM

#include

#include

#include struct process

{

int pid;

int wt,tt,bt;

}

p[100]; void main()

{

int tottt,totwt,avgtt,avgwt,i,j,n; clrscr();

printf("\nEnter Number of process"); scanf("\n%d",&n); for(i=1;i


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totwt=totwt/n;

tottt=tottt/n;

printf("\n\n\n\tAVGWT\tAVGTT");

printf("\n\t%d\t%d",totwt,tottt);

getch();

}

OUTPUT

Enter Number of process3

Enter 1st Burst Time:12

Enter 2st Burst Time:34

Enter 3st Burst Time:56===============================

Process id BT WT TT

===============================

1 12 0 12

2 34 12 46

3 56 46 102

VGWT AVGTT

19 53

RESULT

The program for first come first serve algorithm has been executed and shown the results as above.

VIVA QUESTION

1. What is the Kernel?

A more common definition is that the OS is the one program running at all times on the

computer, usually called the kernel, with all else being application programs.

2. What are Batch systems?

Batch systems are quite appropriate for executing large jobs that need little interaction. The user

can submit jobs and return later for the results.

POSSIBLE QUESTIONS:

1. Given the list of processes, their CPU burst times and arrival times, display/print the Gantt

chart for FCFS


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DESCRIPTION

Associate with each process the length of its next CPU burst. Use these lengths to schedule the

process with the shortest time

Two schemes:

non preemptive once CPU given to the process it cannot be preempted until completes itsCPU burst

preemptive if a new process arrives with CPU burst length less than remaining time ofcurrent executing process, preempt. This scheme is known as the Shortest-Remaining-

Time-First (SRTF) SJF is optimal gives minimum average waiting time for a given set ofprocesses objective


Performs SJF scheduling ie) the process that has the shortest burst time is processed first

ADVANTAGES

o simple

o easy to understando shortest job is served

first

DISADVANTAGES

Long-burst (CPU-intensive) processes are hurt with a long mean waiting time. In fact, if short-

burst processes are always available to run, the long-burst ones may never get scheduled.

Moreover, the effectiveness of meeting the scheduling criteria relies on our ability to estimate the

CPU burst time.

ALGORITHM:


2. Get the number of processes and their burst time.

3. Initialize the waiting time for process 1 is 0.

4. The processes are stored according to their burst time.



EX.NO:4 (b)

DATE:

IMPLEMENTATION OF SJF SCHEDULING


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7. The average waiting time and turn around time are displayed.Stop the program

PROGRAM

#include

#include


{

int pid;

int wt,tt,bt;

}

p[100]; void main()

{

struct process temp;




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p[i].pid=temp.pid;

temp.bt=p[j].bt;

p[j].bt=p[i].bt; p[i].bt=temp.bt; */ temp=p[j]; p[j]=p[i];

p[i]=temp;} } }

p[1].wt=0;

p[1].tt=p[1].bt+p[1].wt;

i=2;

while(i


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Enter 3 Burst Time: 7



===================================Process id BT WT TT

===================================

4 2 0 2

2 4 2 6

3 7 6 13

1 8 13 21

5 9 21 30

AVGWT AVGTT

8 14

RESULT:

The program for shortest job first algorithm has been executed and shown the results as above.

VIVA QUESTION:

1. What are multiprocessor systems & give their advantages?

Multiprocessor systems also known as parallel systems or tightly coupled systems are

systems that have more than one processor in close communication, sharing the computer bus, the

clock and sometimes memory & peripheral devices. Their main advantages are

Increased throughput

Economy of scale

Increased reliability

2. What is a process state and mention the various states of a process?

As a process executes, it changes state. The state of a process is defined in part by the

current activity of that process. Each process may be in one of the following states:

NewRunning

Waiting


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Ready

Terminated

POSSIBLE QUESTION:

1 . Given the list of processes, their CPU burst times and arrival times, display/print the Ganttchart for SJF


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DESCRIPTION

Each process gets a small unit of CPU time (time quantum), usually 10-100 milliseconds. After

this time has elapsed, the process is preempted and added to the end of the ready queue.

If there are nprocesses in the ready queue and the time quantum is q, then each process gets 1/n of

the CPU time in chunks of at most q time units at once. No process waits more

than (n-1)q time units.

Performance

q large -FIFOq small- q must be large with respect to context switch, otherwise overhead is too high


Performs round robin scheduling ie) the process that is assigned with a Quantum time and the

process is processed for the given quantum time in fcfs fashion.

ADVANTAGES:

simple,

low overhead,

works for interactive systems

DISADVANTAGES:

o if quantum is too small, too much time wasted in context switching

o if too large (i.e., longer than mean CPU burst), approaches

ALGORITHM:


2. Get the number of processes, their burst time and time slice for each process.

3. Calculate the total burst time.

4. To check whether the burst time of process is less then the time slice, the required time

only allotted to the process.

5. If the burst time of process is greater than the time slice one time slice is allotted for the

process and burst time is subtracted by one time slice.

6. Step 4 and 5 is repeated up to process burst time is 0.

EX.NO:5(a)

DATE:

IMPLEMENTATION OF ROUND ROBIN SCHEDULING


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PROGRAM

#include


{

int pid,bt,tt,wt; };

int main()

{

struct process x[10],p[30]; int i,j,k,tot=0,m,n;

float wttime=0.0,tottime,a1,a2; clrscr();

printf("\nEnter No.of process\t"); scanf("%d",&n); for(i=1;i


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{

p[k].wt=p[k-1].tt; p[k].tt=p[k].wt+m; x[i].bt=x[i].bt-m; k++;

} } }

}

printf("\nprocess id\ttwt\ttt"); for(i=1;i


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3 17 18

Average Waiting Time: 20.000000

Average TurnAround Time:26.000000

RESULT:

The program for implementation of round robin scheduling has been executed and shown theresults as above.

VIVA QUESTION

1. Define CPU scheduling.

CPU scheduling is the process of switching the CPU among various processes. CPU

scheduling is the basis of multi programmed operating systems. By switching the CPU among

processes, the operating system can make the computer more productive.

2. What is preemptive and non preemptive scheduling?

Under non preemptive scheduling once the CPU has been allocated to a process, the

process keeps the CPU until it releases the CPU either by terminating or switching to the waiting

state. Preemptive scheduling can preempt a process which is utilizing the CPU in between its

execution and give the CPU to another process.

POSSIBLE QUESTION:


chart for Round robin.2. Given the list of processes, their CPU burst times and arrival times, display/print the Gantt

chart for Round robin. , compute and print the average waiting time and average

turnaround time


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DESCRIPTION

A priority number (integer) is associated with each process

The CPU is allocated to the process with the highest priority (smallest integer highest priority)

- Preemptive

- non preemptive

SJF is a priority scheduling where priority is the predicted next CPU burst time

Problem Starvation low priority processes may never execute

Solution Aging as time progresses increase the priority of the process

Performs priority scheduling ie) the process that is assigned with a highest priority is processed

first.

ADVANTAGES:

simple,

low overhead,

works for interactive systems

DISADVANTAGES:

The job remains in the queue for a long time.

ALGORITHM:


2. Get the number of processes, their burst time and priority.

3. Initialize the waiting time for process 1 is 0.4. Based upon the priority processes are arranged.








EX.NO:5(b)

DATE:

IMPLEMENTATION OF PRIORITY SCHEDULING


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PROGRAM:

#include

#include


{

int pid;

int wt,tt,bt,prior;

}

p[100],temp; void main()

{




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totwt=tottt=0;

i=1;

printf("\n\t===============================");

printf("\n\tPSSID\tBT\tWT\tTT");printf("\n\t===============================");

while(i


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===============================

PSSID BT WT TT

===============================

15 0 5

2 7 5 12

3 8 12 20

AVGWT AVGTT

5 12

RESULT

The program for priority scheduling has been executed and shown the results as above.

VIVA QUESTION:

1. Define throughput?

Throughput in CPU scheduling is the number of processes that are completed per unit time.

For long processes, this rate may be one process per hour; for short transactions, throughput might

be 10 processes per second.2. What is turnaround time?

Turnaround time is the interval from the time of submission to the time of completion of a

process. It is the sum of the periods spent waiting to get into memory, waiting in the ready queue,

executing on the CPU, and doing I/O

POSSIBLE QUESTION:


chart for Priority Scheduling.


chart for Priority Scheduling. compute and print the average waiting time and average

turnaround time


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6. The data in the shared memory is read by the child process using the shnot pointer

7. Now, detach and rebase the shared memory

8. Stop the program

PROGRAM:

#include

#include

#include

main()

{

int shmid;

key_t key=0*10; shmid=shmget(key,100,IPC_CREAT|0666); if(shmid


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results as above.

VIVA QUESTION:

1.What is process control block?

Each process is represented in the operating system by a process

It contains the following information:

Process state

Program counter

CPU registers

CPU-scheduling information

Memory-management information

Accounting information I/O

status information

2. What are the use of job queues, ready queues & device queues?

As a process enters a system, they are put into a job queue. This queue consists of all jobs in the

system. The processes that are residing in main memory and are ready & waiting to execute are

kept on a list called ready queue. The list of processes waiting for a particular I/O device is kept in

the device queue

POSSIBLE QUESTION:

1. Developing Application using Inter Process Communication using shared memory)

2. Developing Application using Inter Process Communication using message queues)


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DESCRIPTION

Using pipes for establishing a communication between two processes. As a first step we

need to identify two executables that need to communicate. As an example, consider a case where

one process gets a character string input and communicates it to the other process which reverses

strings. Then we have two processes which need to communicate. Next we define a pipe and

connect it between the processes to facilitate communication. One process gets input strings and

writes into the pipe. The other process, which reverses strings, gets its input (i.e. reads) from the

pipe.

Figure explains how the pipes are used. As shown in the upper part of the figure, a pipe has

an input end and an output end. One can write into a pipe from the input end and read from the

output end. A pipe descriptor, therefore, has an array that stores two pointers. One pointer is for its

input end and the other is for its output end. When a process defines a pipe it gets both the

addresses, as shown in the middle part of Figure. Let us suppose array pp is used to store the

descriptors. pp[0] stores the write end address and pp[1] stores the read end address. Suppose two

processes, Process A and Process B, need to communicate, then it is imperative that the process

which writes closes its read end of the pipe and the process which read closes its write end of the

pipe. Essentially, for a communication from Process A to process B the following should happen.

Process A should keep its write end open and close read end of the pipe. Similarly, Process B

should keep its read end open and close its write end.


To use these pipes, we will write two program's one to represent the server and other to represent

the client. The server will read from the pipe fifo_server to which the client will send a request. On

receiving the request, the server will send the information to the client on fifo_client.

ADVANTAGES:

Speed of communication

This method is available on any platform (Windows 95/98 as well as Windows NT).

EX.NO:6(b)

DATE:

IMPLEMENTATION OF PRIORITY SCHEDULING


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DISADVANTAGES:

Synchronizing access

security

ALGORITHM:1. Start the program.

2. Create the child process using fork().

3. Create the pipe structure using pipe().

4. Now close the read end of the parent process using close().

5. Write the data in the pipe using write().

6. Now close the write end of child process using close().

7. Read the data in the pipe using read().

8. Display the string.


PROGRAM:

#include

main()

{

int fd[3],pid;

char *msg=("OS LAB\n"); char buff[25];

pipe(fd);

pid=fork();

if(pid==0)

{

puts("child process\n"); close(fd[0]); write(fd[1],msg,30);

}

else

{

sleep(1);

puts("parent process\n"); close(fd[1]); read(fd[0],buff,30); printf("%s",buff);

}

}


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OUTPUT:

[cse2@localhost ~]$ cc pipe.c

[cse2@localhost ~]$ ./a.out child

process

parent process

OS LAB

[cse2@localhost ~]$

RESULT

The program for interprocess communication using pipe process has been executed and shown

results as above

VIVA QUESTION:

What are the various file operations?

The six basic file operations are

Creating a file

Writing a file

Reading a file

Repositioning within a file

Deleting a fileTruncating a file

2. What are the information associated with an open file?

Several pieces of information are associated with an open file which may be:

File pointer

File open count

Disk location of the file Accessrights

Possible Question:

1 Developing Application using Inter Process Communication (using shared memory, or message queues)


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DESCRIPTION

This is an illustration of a solution to the classic producer-consumer (bounded-buffer) problem

using semaphores.

CONCEPT Producers produce items to be stored in the buffer. Consumers remove and consume

items which have been stored. Mutual exclusion must be enforced on the buffer itself. Moreover,

producers can store only when there is an empty slot, and consumers can remove only when there

is a full slot. Three semaphores are used. The binary semaphore mutex controls access to the buffer

itself. The counting semaphore empty keeps track of empty slots, and the counting semaphore fullkeeps track of full slots. In this example, the buffer is implemented as an array of size MAX

treated as a circular (ring) buffer. Variables in and out give the index of the next position for

putting in and taking out (if any). Variable count gives the number of items in the buffer.


one or more producers are generating data and placing these in a buffer

a single consumer is taking items out of the buffer one at time

only one producer or consumer may access the buffer at any one time

ADVANTAGES:

Effective resource utilization

DISADVANTAGES:

A semaphore does not keep track of which of the resources are free.

This includes:

Requesting a resource and forgetting to release it releasing aresource that was never requested holding a resource for along time without needing itusing a resource without requesting it first (or after releasing it).

ALGORITHM:


2. Declare the variables in the type of pthread_t as tid_produce tid_consume.

3. Declare a structure for semaphore variables.

EX. NO: 7PRODUCER-CONSUMER PROBLEM USING SEMAPHORES.DATE:


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4. During run time read the number of items to be produced and consumed.

5. Declare and define semaphore function for creation and destroy.

6. Define producer function.

7. Define consumer function.8. Call producer and consumer function.

9. Stop the execution.

PROGRAM:

#include #include

#include #define NBUFF 10

int nitems; struct {

int buff[NBUFF];

sem_t mutex, nempty, nstored; } shared;

void *produce (void *); void *consume (void *);

int main(int argc, char **argv)

{

pthread_t tid_produce, tid_consume; if(argc !=2)

{printf("Useage: filename "); return 0;

}

printf ("\n\n Producer - Consumer Problem using Semaphore\n"); printf (" --------------------

-----------------------\n\n"); nitems=atoi(argv[1]);

sem_init(&shared.mutex,0,1); sem_init(&shared.nempty,0,NBUFF);

sem_init(&shared.nstored,0,0); pthread_setconcurrency(2);

pthread_create(&tid_produce,NULL,produce,NULL);pthread_create(&tid_consume,NULL,consume,NULL);

pthread_join(tid_produce,NULL); pthread_join(tid_consume,NULL);

sem_destroy(&shared.mutex);

sem_destroy(&shared.nempty);

sem_destroy(&shared.nstored);

}

void *produce (void *arg)

{


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int i; for(i=0;i


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Producer.....buff[0] = 0

Consumer.....buff[0] = 0







RESULT

The program to implement producer and consumer problem using semaphores has been

executed and shown the results as above.

VIVA QUESTION:

1. What is semaphores?

A semaphore S is a synchronization tool which is an integer value that, apart from

initialization, is accessed only through two standard atomic operations; wait and signal.

Semaphores can be used to deal with the n-process critical section problem. It can be also used to

solve various synchronization problems.

The classic definition of wait

wait (S)

{ }while (S


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2. Define deadlock prevention.Deadlock prevention is a set of methods for ensuring that at least one of the four necessary

conditions like mutual exclusion, hold and wait, no pre- emption and circular wait cannot hold. By

ensuring that that at least one of these conditions cannot hold, the occurrence of a deadlock can be

prevented.

3. Define deadlock avoidance.

An alternative method for avoiding deadlocks is to require additional information about how

resources are to be requested. Each request requires the system consider the resources currently

available, the resources currently allocated to each process, and the future requests and releases of

each possible future deadlock.

POSSIBLE QUESTION:

1. Implement the Producer Consumer problem using semaphores (using UNIX system

calls).

2. Implement the Producer Consumer problem using UNIX system calls.


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DESCRIPTION

Memory Management Algorithms

In an environment that supports dynamic memory allocation, the memory manager must keep a

record of the usage of each allocatable block of memory. This record could be kept by using

almost any data structure that implements linked lists. An obvious implementation is to define a

free list of block descriptors, with each descriport containing a pointer to the next descriptor, a

pointer to the block, and the length of the block. The memory manager keeps a free list pointer and

inserts entries into the list in some order conducive to its allocation strategy. A number of

strategies are used to allocate space to the processes that are competing for memory .

First Fit

Another strategy is first fit, which simply scans the free list until a large enough hole is found.

Despite the name, first-fit is generally better than best-fit because it leads to less fragmentation.

Small holes tend to accumulate near the beginning of the free list, making the memory allocator

search farther and farther each time.Solution:Next Fit

Best Fit

The allocator places a process in the smallest block of unallocated memory in which it will fit. It

requires an expensive search of the entire free list to find the best hole. More importantly, it leads

to the creation of lots of little holes that are not big enough to satisfy any requests. This situation is

calledfragmentation, and is a problem for all memory-management strategies, although it is


The memory segments are allocated with the memory space using First fit and Best Fit techniques.

ADVANTAGES:

effective memory utilization

EX NO : 8MEMORY MANAGEMENT SCHEMES I

FIRST FIT BEST FIT

DATE:


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DISADVANTAGES:

First fit wastes memory space Best Fit more time consuming suffer from external fragmentation

ALGORITHM:


2. Get the number of segments and size.

3. Get the memory requirement and select the option.

4. If the option is 2 call first fit function.

5. If the option is 1 call best fit function.

6. Otherwise exit.

7. For first fit, allocate the process to first possible segment which is free.

8. For best fit, do the following steps.

a. Sorts the segments according to their sizes.

b. Allocate the process to the segment which is equal to or slightly greater than the

process size.


PROGRAM:

#include

#include #define MAXSIZE 25 void printlayout(int[],int ); int

firstfit(int[],int, int); int bestfit(int[],int, int); void main()

{

int i,a[25],n,req,choice,pos,ch; clrscr();

printf("How MAny Segments"); scanf("%d",&n); for(i=0;i


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{

case 1: pos=bestfit(a,n,req); break;

case 2: pos=firstfit(a,n,req);

break;

}

printf("\tBestfit and Firstfit Algorithm\n"); printf("\t______________________________\n\n");

printlayout(a,n);

printf("Your Memory Requirment is :%d\n\n",req); printf("Alloted Memory Region

is:%d\n\n",a[pos]); a[pos]=0;

printf("Do You Want To Continue 1/0"); scanf("%d",&ch);

if(ch==1) goto loop; getch();

}

void printlayout(int a[],int n)

{

int i,j;

printf("\t\tMemory Free List"); printf("\n\t\t_______________\n\n");

printf("\t\t|~~~|\n");

for(i=0;i


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int b[25],i,j,temp,val; for(i=0;i


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| |

| |

| |

| ||500| | --- |

| |

| |

|200| | --- |

| |

| |

| ||300|| --- |

| |

| |

| |

|

|400| | --- |

Your Memory Requirment is :200

Alloted Memory Region is:200

Do You Want To Continue 1/0 1

How Much Is Your Memory Requirment250

1.Bestfit

2.Firstfit

3.Exit

Enter Your Choice 1

Bestfit and Firstfit Algorithm

Memory Free List


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|~~~|

| |

| |

| ||500|

Your Memory Requirment is :250

Alloted Memory Region is:300

Do You Want To Continue 1/0

0

RESULT

The program for best fit and first fit algorithm for memory management has been executed

and shown the results as above.

VIVA QUESTION:

1. What is the main function of the memory-management unit?

The runtime mapping from virtual to physical addresses is done by a hardware device

called a memory management unit (MMU).

2. What are the common strategies to select a free hole from a set of available holes?

The most common strategies are

a. First fit

b. Best fit

c. Worst fit

3. What is virtual memory?

Virtual memory is a technique that allows the execution of processes that may not be

completely in memory. It is the separation of user logical memory from physical memory. This

separation provides an extremely large virtual memory, when only a smaller physical memory isavailable.


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POSSIBLE QUESTION:

1. Implement some memory management schemes I


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DESCRIPTION

Page replacement algorithms are used to decide what pages to page out when a page needs to beallocated. This happens when a page fault occurs and free page cannot be used to satisfy allocation

FIFO:

The frames are empty in the beginning and initially no page fault occurs so it is set to minus

one. When a page fault occurs the page reference string is brought into memory. The operating

system keeps track of all the pages in memory, herby keeping track of the most recently arrived

and the oldest one. If the page in the page reference string is not in memory, the page fault is

incremented and the oldest page is replaced. If the page in the page reference string is in the

memory, take the next page without calculating the page fault. Take the next page in the page

reference string and check if the page is already present in the memory or not. Repeat the process

until all the pages are referred and calculate the page fault for all those pages in the page reference

string for the number of available frames.

LRU :

A good approximation to the optimal algorithm is based on the observation that pages that have

been heavily used in the last few instructions will probably be heavily used again in the next few.

Conversely, pages that have not been used for ages will probably remain unused for a long time.

This idea suggests a realizable algorithm: when a page fault occurs, throw out the page that has

been unused for the longest time. This strategy is called LRU (Least Recently Used) paging


Minimizing the number of (major) page faults (situations where a page must be brought in from

disk) using LRU and FIFO.

ADVANTAGES:


DISADVANTAGES:

Time consuming

EX.NO: 9

DATE:

MEMORY MANAGEMENT SCHEMES II

PAGE REPLACEMENT


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ALGORITHM:

1. Start the program

2. Obtain the number of sequences, number of frames and sequence string from the user3. Now when a page is not in the frame comes, increment the number of page fault and

remove the page that come in the first in FIFO algorithm

4. In LRU algorithm, when a page fault occurs, the page which most recently used is

removed

5. Display the number of faults

Stop the program

PROGRAM:

#include

int m,n,i,j,k,flag,count=0,refer[100],page_frame[100][2],fault=0,min,no_frames; void replace(int z)

{

for(i=0;i


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page_frame[k][1]=++count;

for(j=0;j


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OUTPUT:

Enter the number of reference:10

Enter the number of frames:3

Enter the reference string:7 0 1 2 0 3 0 4 2 6

FIFO ALGORITHM

7 -1 -1

7 0 -1

7 0 1

2 0 1

no page fault 2 3 1 2 3 0 4 3 0 4 2 0 4 2 6

number of page fault is:9

LRU ALGORITHM

7 -1 -1

7 0 -1

7 0 1

RESULT:

The program for page replacement algorithms for memory management has been executed andshown the results as above.

VIVA QUESTION:

1. What is Demand paging?

Virtual memory is commonly implemented by demand paging. In demand paging, thepager brings only those necessary pages into memory instead of swapping in a whole process.

Thus it avoids reading into memory pages that will not be used anyway, decreasing the swap time

and the amount of physical memory needed.

2. What are the various page replacement algorithms used for page replacement?

FIFO page replacement

Optimal page replacement


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LRU page replacement

LRU approximation page replacement

Counting based page replacement

Page buffering algorithm.

POSSIBLE QUESTION:

1. Implement some memory management schemes II


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DESCRIPTION

File Allocation Methods

One main problem in file management is how to allocate space for files so that disk space isutilized effectively and files can be accessed quickly. Three major methods of allocating diskspace are:* Contiguous Allocation* Linked Allocation

* Indexed Allocation.Each method has its advantages and disadvantages. Accordingly, some systems support all three(e.g. Data General's RDOS). More commonly, a system will use one particular method for all files.

Contiguous File Allocation

Each file occupies a set of contiguous block on the diskAllocation using first fit/best fit.A need for compaction

Only starting block and length of file in blocks are needed to work with the fileAllows random access

Problems with files that grow


Allocates blocks of memory for files using file allocation techniques.

ADVANTAGES:


each file occupies set of contiguous blocks on the disk. Random access

DISADVANTAGES:

Time consuming

Wastes lot of memory space

EX.NO: 10

DATE:

FILE ALLOCATION TECHNIQUE-CONTIGUOUS


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ALGORITHM:

1. Start the process

2. Declare the necessary variables

3. Get the number of files

4.Get the total no. of blocks that fit in to the file

5. Display the file name, start address and size of the file. 6.Stop the program

PROGRAM:

#include void main()

{

int i,j,n,block[20],start: printf(Enter the no. of file:\n);

scanf(%d,&n);

printf(Enter the number of blocks needed for each file:\n); for(i=0,i


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File 3 8 6

File 4 14 1

RESULT:

The program for file allocation technique has been executed and shown the results as above.

VIVA VOICE

1. What are the allocation methods of a disk space?

Three major methods of allocating disk space which are widely in use are

a. Contiguous allocation

b. Linked allocation

c. Indexed allocation

2. What is Directory?

The device directory or simply known as directory records information- such as name,

location, size, and type for all files on that particular partition. The directory can be viewed as a

symbol table that translates file names into their directory entries.

Search for a fileCreate a file

Delete a file

Rename a file

List directory

Traverse the file system

POSSIBLE QUESTION:

1. Implement any file allocation technique (Linked, Indexed or Contiguous)

final copy oslab manua1. jjjjjjjjjjj 2

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