Working with Operating
System
Chapter : 2
Operating System
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Operating system is a system software which acts as
an interface between user and computer. It has two
parts : Kernel and Shell. Kernel is responsible for
interacting with hardware and the shell is
responsible for interacting with the user.
The Shell acts as the command interpreter which
takes the commands from the user, interprets them
& takes action accordingly.
Concept of Booting
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Booting means loading or moving the
operating system into the main memory of
computer.
Booting is of two types :
1) Hard Booting
2) Soft Booting
Types of Operating System
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Single Program OS : This OS is a single user OS, so
only one user is executed at a time.
Multiprogram OS : This is multiuser OS. It supports
multiprogramming i.e. more than one user can be
supported at the same time.
Time Sharing OS : This OS uses time sharing technique
to execute multiple programs at a time. Each active user is
given a time slice for the executing of programs.
Real Time OS : In real Time OS jobs have fixed time
deadlines and the jobs have to be completed within their
deadlines.
Multiprocessing OS : is capable of handling more than
one processors as the jobs have to be executed on more
than one processor.
Types of Application Software
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(i) Packages
(ii) Utilities
(iii) Customised Software
(i) Packages : This type of software is
developed keeping in mind the general
requirements for carrying out a specific task.
Many users can use it simultaneously as it
fulfills the general requirements. Example :
Electronic Spreadsheet, DBMS (Database
Management system, Word Processing
Package etc.
Packages
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Word Processing Package is a package that
processes textual matter and creates organized
and flawless documents.
An Electronic Spreadsheet is a program that
accepts data in a tabular form (in rows and
columns) and allows the users to manipulate/
calculate/ analyze data in the desired manner.
A Database Management System (DBMS) is
a package that can handle and manage bulk of
stored data.
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Desktop Publishing software : The software that
handles page layout by combining the functions of a
traditional typesetter and a layout artist, is known as
DTP.
Graphics Software : The application software that
manipulates images is known as Graphics software
and the software that incorporates images, text,
sound, computer animation, and video sequences is
known as multimedia software.
Presentation graphics software : The application
software that can create professional looking visual
aids is called Presentation Graphics Software.
Utilities
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Utilities are those application programs that
assist
the
computer
by
performing
housekeeping functions like backing up disk or
scanning/ cleaning viruses or arranging
information etc.
Some of the important utilities are as follows :
1) Text Editor
2) Backup Utility
3) Compression Utility 4) Disk Defragmentor
5) Antivirus Software
Types of Services provided by OS
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1) Program Execution
2) Handling Input/Output Operations.
3) Manipulation of the file system
4) Error detection and handling
5) Resource allocation
6) Accounting : The OS keeps an account of what
type of functioning is taking place and what type of
errors have occurred.
7) Information and Resource Protection : OS ensures
that information & Resources are used in correct way.
OS functions
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Major functions of OS are listed below :
1) Processor Management
2) Storage ( Memory ) management
3) Information Management
1) Processor Management : Processor management
means managing the process or processor i.e. the
CPU so this function is also termed as CPU
scheduling. The main focus is on increasing the
throughput i.e. the amount of work accomplished in a
given time interval ( e.g. 15 jobs per hour).
Throughput = No. of jobs completed / Total time
taken to complete the jobs
Job Scheduling
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It is the process of assigning priority to
different jobs submitted for execution and to
admit new jobs for processing at appropriate
times.
Process & its states : Process is a program in
execution. During execution process changes
its states i.e. current activity. A process can
have these states : new, active , waiting or
halted
Process States
NEW
ACTIVE
WAITING
HALTING
TYPES OF SCHEDULING
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Non-Preemptive scheduling
Preemptive scheduling
Non-Preemptive scheduling : In this type of
scheduling job always completes before another
scheduling decision is made. Different scheduling
techniques which use non-preemptive scheduling are
:
i) First Come First Serve (FCFS) Scheduling
ii) Shortest job Next (SJN) Scheduling
iii) Deadline Scheduling
Preemptive Scheduling
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In Preemptive scheduling a scheduling
decision can be made even while the job is
executing. Therefore, a preemptive scheduling
may force a job in execution to release the
processor, so that priority job can be executed
first to improve throughput. The techniques
used in preemptive scheduling are :
i) Round Robin scheduling
Ii) Response Ratio Scheduling
Memory Management
CPU
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MEMORY
I/O SYSTEM
Memory plays a central role in computer system as
both CPU and I/O system interact with memory.
Every program must be assigned some memory area
and loaded into memory in order to be executed.
Various approaches for memory management are
given as under :
1) Contiguous Storage Allocation
2) Non Contiguous Storage Allocation
3) Virtual Storage Using Paging
Information Management
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OS has a component called ‘Information management
component and is structured as follows :
i) Physical IOCS (Input-Output control system) is
responsible to handle the device for I/O operation and
for error recovery.
ii) Logical IOCS is responsible for efficient
organization and access of data on IO devices e.g.
open a file, read a record, delete a record etc.
Iii) File system is responsible for protection and
controlled sharing of files.
Some commonly Used OS
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Linux
Unix
Windows
MS-DOS
OPEN SOURCE SOFTWARE
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Freely accessible
Freely used
Freely changed,improved.
Freely copied and distributed
Payments may or may not required to be made
Source code is available.
Proprietory Software
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Neither open nor freely available.
Source code not available.
Further distribution and modification is either
forbidden or requires special permission by the
supplier or vendor.
Freeware
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Freely accessible
Freely used
No modifications can be made.
Freely copied and distributed
No payments required to be made
Source code not available.
Freeware is often used in marketing situations in
order to sell additional products. E.g. Microsoft
Internet Explorer
Shareware
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Freely accessible
Freely used
No modifications can be made.
Freely copied and distributed
A license fee has to be paid after a certain period of
time e.g. antivirus
Source code not available.
Its objective is to make the software available to try
for as many users as possible.
Representing Characters in Memory
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ASCII (American Standard Code for Information
Interchange) is the most widely used alphanumeric
code in most microcomputers and minicomputers and
in many mainframes. The ASCII code is a 7-bit code,
and so it has 27 = 128 possible code groups to
represent different characters.
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ISCII (Indian Standard Code for Information
Interchange) is an 8-bit code capable of coding 256
characters. ISCII code retains all ASCII characters
and offers coding for Indian scripts also. Thus it is
also called Indian Scripts Code for Information
Interchange.
UNICODE (Universal Coding)
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Unicode provides a unique number for every
character, no matter what the platform, no
matter what the program, no matter what the
language. The Unicode Standard has been
adopted by such industry leaders as Microsoft,
Oracle, IBM etc. Unicode version 3.0
represented 49,194 characters, whereas
Unicode version 3.1 has added many more
characters, making the character count to
94,140.