Introduction and What is an Operating System

8/8/2019 Introduction and What is an Operating System

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Operating SystemBCA 3rd Notes

[operating system overview,process, memory, device, filemanagement system,Concurrent

programming]

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0

Sunil Insan0999608585009729957457


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INTRODUCTION

Computer software can be divided into two main categories:

application software and system software. Application

software consists of the programs for performing tasks

particular to the machines utilization. This software is

designed to solve a particular problem for users. Examples

of application software include spreadsheets, database

systems, desktop publishing systems, program development

software, and games.

On the other hand, system software is more transparent and

less noticed by the typical computer user. This software

provides a general programming environment in which

programmers can create specific applications to suit their

needs. This environment provides new functions that are not

available at the hardware level and performs tasks related to

executing the application program. System software acts as

an interface between the hardware of the computer and the

application software that users need to run on the computer.

The most important type of system software is the operating

system.

An Operating System (OS) is a collection of programs that

acts as an interface between a user of a computer and the

computer hardware. The purpose of an operating system is

to provide an environment in which a user may execute the

programs


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An Operating System (OS) is a collection of programs that

acts as an interface between a user of a computer and the

computer hardware. The purpose of an operating system is

to provide an environment in which a user may execute the

programs. Operating Systems are viewed as resource

managers. The main resource is the computer hardware in

the form of processors, storage, input/output devices,

communication devices, and data. Some of the operating

system functions are: implementing the user interface,

sharing hardware among users, allowing users to share data

among themselves, preventing users from interfering with

one another, scheduling resources among users, facilitating

input/output, recovering from errors, accounting for resource

usage, facilitating parallel operations, organizing data for

secure and rapid access, and handling network

communications.

WHAT IS AN OPERATING SYSTEM?


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CLASSIFICATION OF OPERATING SYSTEMS

In this section we will discuss about the different types of

operating systems. These are.

Batch Processing Operating System


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In a batch processing operating system environment , the

user has no interaction with the job during its processing .

Some of the examples use of the batch operating system are

Payroll, stock control and billing systems.

ADVANTAGES

1 .resourse management and allocation is very easy.

2.faster than serial proceesing

DISADVANTAGES

1. utilization of cpu is very poor.

2. lack of interaction between the user and the job while

job is executing.


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3. difficult to provide the desired priorty.

Time Sharing

Another mode for delivering computing services is provided

by time sharing operating systems. In this environment a

computer provides computing services to several or many

users concurrently on-line. Here, the various users are

sharing the central processor, the memory, and other

resources of the computer system in a manner facilitated,

controlled, and monitored by the operating system. The

user, in this environment, has nearly full interaction with the

program during its execution, and the computers response

time may be expected to be no more than a few second.

INTERACTIVE (OR on line) O.S

An interactive system provides on line communication

between the user and the system. The user gives

instructions to the operating system or to a program

directly, and receives an immediate response. Usually, a

keyboard is used to provide input and a monitor is used to

provide output. When the operating system finishes the

execution of one instruction , it seeks the next instructionfrom the users keyboard.

Some of the examples use of the on line operating

system are Electricity an gas boards, banking stock


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exchanges and stock control. It is sed in those applicatins

where on line communication between user and system are

necessary.

REAL TIME O.S

Another type of operating system is the real time

system. These systems are characterized by having time as

a key parameter. The real time operating systems are

designed to service those applications where response time

is of the essence in order to prevent error,

misrepresentation or even disaster. A very important part of

an RTOS is managing the resources of the computer so that

a particular operation executes in precisely the same

amount of time every time it occurs. In a complex machine,

having a part move more quickly just because systemresources are available may be just as catastrophic as

having it not move at all because the system is busy.

Examples of real time operating systems are those

which handle airlines reservations, machine tool control, and

monitoring of a nuclear power station. The systems, in this

case, are designed to be interrupted by external signals thatrequire the immediate attention of the computer system.

ADVANTAGES

1. response time is very lesss.


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2. 24 hours service provider.

3. provide information up to minute

4. large memory.

5. better throughput.

DISADVANTAGES

1. VERY COSTY

2. complex communication systems

3. large main memory and secondary storage required.

MULTI PROGRAMMING O.S

A multiprogramming operating system is a system that

allows more than one active user program (or part of user

program) to be stored in main memory simultaneously.

Thus, it is evident that a time-sharing system is a

multiprogramming system, but note that a

multiprogramming system is not necessarily a time-sharing

system. A batch or real time operating system could, and

indeed usually does, have more than one active user

program simultaneously in main storage.

Multiprogramming refers to keeping several programs in

memory at the same time and executing them concurrently.

The cpu switches from one program to another almost

instantaneously. Since the operating speed of cpu is much

fasters than I\O operations. hence in multi programming

system , when one program is waiting for I\O transfer ,

there is another program is ready to wuse the cpu.


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ADVANTAGES

1. CPU is fully utilized.

2. shorter response time

3. allows more than one active user program (or part of

user program) to be stored in main memory

simultaneously.

4. improved primary storage allocation.

DISADVANTAGES

1. large main memory is required.

2. computers design for multiprogramming must provide

some type of memory protection mechanism to prevent

a program in one memory partition, from changing

information or instruction of a program in another

memory partition.

DISTRIBUTEDOPERATINGSYSTEM

A distributed system uses multiple processors to serve

multiple real time applications and multiple classes of users .

each central processing unit specializes in performing

particular functions of serving a particular functions or

serving a particular class of users. Data processing jobs

distributed among the processors accordingly to which one

can perform each job most efficiently. The Central

Processors may all be located at the same site, but more


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typically are geographically scattered and connected b date

communication lines, forming a distributed network.

Far distant places may be linked through satellite

transmission channels or ground microwave systems and

within same city through telephone lines or special coaxial

cables.

Thus, in distributed operating systems, each processor has

its own memory and executed its own jobs and shared jobs.

The processors communicate with one another through

various communication media. Such systems are also known

as loosely coupled systems

ADVANTAGES OF DISTRIBUTED SYSTEMS INCLUDE :

. Increased system availability and faster system response

time.

. Better service to the customers.

. Less risk of system breakdown, therefore, better reliability.

.Level of expertise required is less.

MULTIPROCESSOR SYSTEMS

Although single-processor systems are most

common, multiprocessor systems (also known as


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parallel systems or tightly coupled systems) are

growing in importance. Such systems have two or more

processors in close communication sharing the computer

bus and sometimes the clock, memory, and peripheral

devices.

Multiprocessor systems have three main advantages:

1. Increased throughput. By increasing the number of

processors, we expect to get more work done in less time.

The speed-up ratio with N processors is notN, however;

rather, it is less than N. When multiple processors cooperate

on a task, a certain amount of overhead is incurred in

keeping all the parts working correctly. This overhead, plus

contention for shared resources, lowers the expected gain

from additional processors. Similarly, N programmers

working closely together do not produce N times the amount

of work a single programmer would produce.

2. Economy of scale. Multiprocessor systems can cost lessthan equivalent

multiple single-processor systems, because they can share

peripherals,


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mass storage, and power supplies. If several progr*-ams

operate on the

same set of data, it is cheaper to store those data on one

disk and to have

all the processors share them than to have many computers

with local

disks and many copies of the data.

3. Increased reliability. If functions can be distributed

properly among

several processors, then the failure of one processor will not

halt the

system, only slow it down. If we have ten processors and

one fails, then

each of the remaining nine processors can pick up a share of

the work of

the failed processor. Thus, the entire system runs only 10

percent slower,

rather than failing altogether.


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Networking Operating System

A networked computing system is a collection of physical

interconnected computers. The operating system of each of

the interconnected computers must contain, in addition to

its own stand-alone functionality, provisions for handing

communicationand transfer of program and data among the

other computers with which it is connected.

Network operating systems are not fundamentally

different from single processor operating systems. They

obviously need a network interface controller and some low-

level software to drive it, as well as programs to achieve

remote login and remote files access, but these additions do

not change the essential structure of the operating systems.

Introduction and What is an Operating System

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