Working with Operating Working with Operating SystemSystem

Chapter : 2Chapter : 2

Operating SystemOperating System Operating system is a system software which acts as Operating system is a system software which acts as

an interface between user and computer. It has two an interface between user and computer. It has two parts : parts : KernelKernel and and ShellShell. Kernel is responsible for . Kernel is responsible for interacting with hardware and the shell is interacting with hardware and the shell is responsible for interacting with the user.responsible for interacting with the user.

The Shell acts as the command interpreter which The Shell acts as the command interpreter which takes the commands from the user, interprets them takes the commands from the user, interprets them & takes action accordingly.& takes action accordingly.

Concept of BootingConcept of Booting

Booting means loading or moving the Booting means loading or moving the operating system into the main memory of operating system into the main memory of computer.computer.

Booting is of two types :Booting is of two types : 1) Hard Booting1) Hard Booting 2) Soft Booting2) Soft Booting

Types of Operating SystemTypes of Operating System Single Program OSSingle Program OS : This OS is a single user OS, so : This OS is a single user OS, so

only one user is executed at a time.only one user is executed at a time. Multiprogram OS : This is multiuser OS. It supports Multiprogram OS : This is multiuser OS. It supports

multiprogramming i.e. more than one user can be multiprogramming i.e. more than one user can be supported at the same time.supported at the same time.

Time Sharing OSTime Sharing OS : This OS uses time sharing technique : This OS uses time sharing technique to execute multiple programs at a time. Each active user is to execute multiple programs at a time. Each active user is given a time slice for the executing of programs.given a time slice for the executing of programs.

Real Time OSReal Time OS : In real Time OS jobs have fixed time : In real Time OS jobs have fixed time deadlines and the jobs have to be completed within their deadlines and the jobs have to be completed within their deadlines.deadlines.

Multiprocessing OSMultiprocessing OS : is capable of handling more than : is capable of handling more than one processors as the jobs have to be executed on more one processors as the jobs have to be executed on more than one processor.than one processor.

Types of Application SoftwareTypes of Application Software (i) Packages(i) Packages (ii) Utilities(ii) Utilities (iii) Customised Software(iii) Customised Software (i) Packages(i) Packages : This type of software is : This type of software is

developed keeping in mind the general developed keeping in mind the general requirements for carrying out a specific task. requirements for carrying out a specific task. Many users can use it simultaneously as it Many users can use it simultaneously as it fulfills the general requirements. Example : fulfills the general requirements. Example : Electronic Spreadsheet, DBMS (Database Electronic Spreadsheet, DBMS (Database Management system, Word Processing Management system, Word Processing Package etc.Package etc.

PackagesPackages Word Processing PackageWord Processing Package is a package that is a package that

processes textual matter and creates organized processes textual matter and creates organized and flawless documents.and flawless documents.

An An Electronic SpreadsheetElectronic Spreadsheet is a program that is a program that accepts data in a tabular form (in rows and accepts data in a tabular form (in rows and columns) and allows the users to manipulate/ columns) and allows the users to manipulate/ calculate/ analyze data in the desired manner.calculate/ analyze data in the desired manner.

A A Database Management System (DBMS)Database Management System (DBMS) is is a package that can handle and manage bulk of a package that can handle and manage bulk of stored data.stored data.

Desktop Publishing softwareDesktop Publishing software : The software that : The software that handles page layout by combining the functions of a handles page layout by combining the functions of a traditional typesetter and a layout artist, is known as traditional typesetter and a layout artist, is known as DTP.DTP.

Graphics SoftwareGraphics Software : The application software that : The application software that manipulates images is known as Graphics software manipulates images is known as Graphics software and the software that incorporates images, text, and the software that incorporates images, text, sound, computer animation, and video sequences is sound, computer animation, and video sequences is known as multimedia software.known as multimedia software.

Presentation graphics softwarePresentation graphics software : The application : The application software that can create professional looking visual software that can create professional looking visual aids is called Presentation Graphics Software.aids is called Presentation Graphics Software.

UtilitiesUtilities

UtilitiesUtilities are those application programs that are those application programs that assist the computer by performing assist the computer by performing housekeeping functions like backing up disk housekeeping functions like backing up disk or scanning/ cleaning viruses or arranging or scanning/ cleaning viruses or arranging information etc.information etc.

Some of the important utilities are as follows :Some of the important utilities are as follows : 1) Text Editor1) Text Editor 2) Backup Utility2) Backup Utility 3) Compression Utility 4) Disk Defragmentor3) Compression Utility 4) Disk Defragmentor 5) Antivirus Software5) Antivirus Software

Types of Services provided by OSTypes of Services provided by OS

1) Program Execution1) Program Execution 2) Handling Input/Output Operations.2) Handling Input/Output Operations. 3) Manipulation of the file system3) Manipulation of the file system 4) Error detection and handling4) Error detection and handling 5) Resource allocation5) Resource allocation 6) Accounting : The OS keeps an account of what 6) Accounting : The OS keeps an account of what

type of functioning is taking place and what type of type of functioning is taking place and what type of errors have occurred.errors have occurred.

7) Information and Resource Protection : OS ensures 7) Information and Resource Protection : OS ensures that information & Resources are used in correct way.that information & Resources are used in correct way.

OS functionsOS functions Major functions of OS are listed below :Major functions of OS are listed below : 1) Processor Management1) Processor Management 2) Storage ( Memory ) management2) Storage ( Memory ) management 3) Information Management3) Information Management 1) Processor Management1) Processor Management : Processor management : Processor management

means managing the process or processor i.e. the means managing the process or processor i.e. the CPU so this function is also termed as CPU CPU so this function is also termed as CPU scheduling. The main focus is on increasing the scheduling. The main focus is on increasing the throughput i.e. the amount of work accomplished in a throughput i.e. the amount of work accomplished in a given time interval ( e.g. 15 jobs per hour).given time interval ( e.g. 15 jobs per hour).

Throughput = No. of jobs completed / Total time Throughput = No. of jobs completed / Total time taken to complete the jobstaken to complete the jobs

Job SchedulingJob Scheduling

It is the process of assigning priority to It is the process of assigning priority to different jobs submitted for execution and to different jobs submitted for execution and to admit new jobs for processing at appropriate admit new jobs for processing at appropriate times.times.

Process & its statesProcess & its states : Process is a program in : Process is a program in execution. During execution process changes execution. During execution process changes its states i.e. current activity. A process can its states i.e. current activity. A process can have these states : new, active , waiting or have these states : new, active , waiting or haltedhalted

Process StatesProcess States

ACTIVENEW

WAITING

HALTING

TYPES OF SCHEDULINGTYPES OF SCHEDULING

Non-Preemptive schedulingNon-Preemptive scheduling Preemptive schedulingPreemptive scheduling Non-Preemptive schedulingNon-Preemptive scheduling : In this type of : In this type of

scheduling job always completes before another scheduling job always completes before another scheduling decision is made. Different scheduling scheduling decision is made. Different scheduling techniques which use non-preemptive scheduling techniques which use non-preemptive scheduling are :are :

i) First Come First Serve (FCFS) Schedulingi) First Come First Serve (FCFS) Scheduling ii) Shortest job Next (SJN) Schedulingii) Shortest job Next (SJN) Scheduling iii) Deadline Schedulingiii) Deadline Scheduling

Preemptive SchedulingPreemptive Scheduling

In In Preemptive schedulingPreemptive scheduling a scheduling a scheduling decision can be made even while the job is decision can be made even while the job is executing. Therefore, a preemptive scheduling executing. Therefore, a preemptive scheduling may force a job in execution to release the may force a job in execution to release the processor, so that priority job can be executed processor, so that priority job can be executed first to improve throughput. The techniques first to improve throughput. The techniques used in preemptive scheduling are :used in preemptive scheduling are :

i) Round Robin schedulingi) Round Robin scheduling Ii) Response Ratio SchedulingIi) Response Ratio Scheduling

Memory ManagementMemory Management

MemoryMemory plays a central role in computer system as plays a central role in computer system as both CPU and I/O system interact with memory. both CPU and I/O system interact with memory. Every program must be assigned some memory area Every program must be assigned some memory area and loaded into memory in order to be executed. and loaded into memory in order to be executed. Various approaches for memory management are Various approaches for memory management are given as under :given as under :

1) Contiguous Storage Allocation1) Contiguous Storage Allocation 2) Non Contiguous Storage Allocation2) Non Contiguous Storage Allocation 3) Virtual Storage Using Paging3) Virtual Storage Using Paging 4) Virtual Storage Using Segmentation4) Virtual Storage Using Segmentation

CPU MEMORY I/O SYSTEM

Information ManagementInformation Management

OS has a component called ‘Information management OS has a component called ‘Information management component and is structured as follows :component and is structured as follows :

i) i) Physical IOCS (Input-Output control system)Physical IOCS (Input-Output control system) is is responsible to handle the device for I/O operation and responsible to handle the device for I/O operation and for error recovery.for error recovery.

ii) ii) Logical IOCSLogical IOCS is responsible for efficient is responsible for efficient organization and access of data on IO devices e.g. organization and access of data on IO devices e.g. open a file, read a record, delete a record etc.open a file, read a record, delete a record etc.

Iii) File system is responsible for protection and Iii) File system is responsible for protection and controlled sharing of files.controlled sharing of files.

Some commonly Used OSSome commonly Used OS

LinuxLinux UnixUnix WindowsWindows MS-DOSMS-DOS

OPEN SOURCE SOFTWAREOPEN SOURCE SOFTWARE

Freely accessibleFreely accessible Freely usedFreely used Freely changed,improved.Freely changed,improved. Freely copied and distributedFreely copied and distributed Payments may or may not required to be Payments may or may not required to be

mademade Source code is available.Source code is available.

Proprietory SoftwareProprietory Software

Neither open nor freely available.Neither open nor freely available. Source code not available.Source code not available. Further distribution and modification is either Further distribution and modification is either

forbidden or requires special permission by the forbidden or requires special permission by the supplier or vendor.supplier or vendor.

FreewareFreeware

Freely accessibleFreely accessible Freely usedFreely used No modifications can be made.No modifications can be made. Freely copied and distributedFreely copied and distributed No payments required to be madeNo payments required to be made Source code not available.Source code not available. Freeware is often used in marketing situations in Freeware is often used in marketing situations in

order to sell additional products. E.g. Microsoft order to sell additional products. E.g. Microsoft Internet ExplorerInternet Explorer

SharewareShareware

Freely accessibleFreely accessible Freely usedFreely used No modifications can be made.No modifications can be made. Freely copied and distributedFreely copied and distributed A license fee has to be paid after a certain period of A license fee has to be paid after a certain period of

time e.g. antivirustime e.g. antivirus Source code not available.Source code not available. Its objective is to make the software available to try Its objective is to make the software available to try

for as many users as possible.for as many users as possible.

Representing Characters in MemoryRepresenting Characters in Memory ASCIIASCII (American Standard Code for Information (American Standard Code for Information

Interchange)Interchange) is the most widely used alphanumeric is the most widely used alphanumeric code in most microcomputers and minicomputers and code in most microcomputers and minicomputers and in many mainframes. The ASCII code is a 7-bit code, in many mainframes. The ASCII code is a 7-bit code, and so it has 2and so it has 277 = 128 possible code groups to = 128 possible code groups to represent different characters.represent different characters.

ISCII (Indian Standard Code for Information ISCII (Indian Standard Code for Information Interchange)Interchange) is an 8-bit code capable of coding 256 is an 8-bit code capable of coding 256 characters. ISCII code retains all ASCII characters characters. ISCII code retains all ASCII characters and offers coding for Indian scripts also. Thus it is and offers coding for Indian scripts also. Thus it is also called Indian Scripts Code for Information also called Indian Scripts Code for Information Interchange.Interchange.

UNICODE (Universal Coding)UNICODE (Universal Coding)

Unicode provides a unique number for every Unicode provides a unique number for every character, no matter what the platform, no character, no matter what the platform, no matter what the program, no matter what the matter what the program, no matter what the language. The Unicode Standard has been language. The Unicode Standard has been adopted by such industry leaders as Microsoft, adopted by such industry leaders as Microsoft, Oracle, IBM etc. Unicode version 3.0 Oracle, IBM etc. Unicode version 3.0 represented 49,194 characters, whereas represented 49,194 characters, whereas Unicode version 3.1 has added many more Unicode version 3.1 has added many more characters, making the character count to characters, making the character count to 94,140.94,140.