5 operating systems.ppt

7/27/2019 5 Operating Systems.ppt

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Operating Systems

Unit 2


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Introduction

An OS is a software program that loadsautomatically and controls just about everythingon the computer.

It does the following:

a) Controls computers hardware.

b) runs the computers programs.

c) organizes files.. When the computer starts, it starts the OS that

takes the control of the machine.


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Definition

No formal agreed definition:

Generally defined as A group of programs

designed to serve the basic purpose of

controlling the allocation and use of the

resources among various users and tasks. Alsoto provide an interface between the computer

hardware and programmer.


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Functions of an OS

Primary Functions are:1.Booting

2. Housekeeping functions ( Formatting,

coordinating, etc)3.User interface

4. Managing computer resources ( Memory

management, Processor management, Devicemanagement, Information management)

5.Managing tasks.


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Booting

When the computer is powered on , the process

that takes place till the computer is ready toaccept the work is called Booting.

This process is actually performed by a

permanently stored program in the ROM of thesystem called bootstrap

This is also referred as BIOS which gets executedfirst and then copies the OS programs into the

memory of the system. After loading the bootstrap, the computer runs

the diagnostic routines to test the other parts.


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House keeping operations

In this, the OS arranges and organizes the files,

backups the files and format a floppy (if

needed).


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Managing Computer Resources

Memory Management

The OS optimizes memory by allocating thememory to various applications or processes

running on the system and removes unwanted

data from memory. Processor Management

The OS does the control and allocation of CPU

time to various processes. A scheduler(part ofOS)selects which ready program to be run next

and specifies the CPU time allocated to it


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Device Management

The I/O devices, storage devices (called as

peripheral devices) are handled and managedfor single use of multiuse options.

Information Management

Here the OS keeps track of the file storageand retrieval of data or program files on

various locations and makes them available

when required.


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Managing tasks

A task is any single operation performed on the

computer.

But using the computer for just a single task is

inefficient.

The OS manages a variety of tasks by

Multitasking, Multiprogramming, time sharing,

Multiprocessing.


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Types of OS

OS cab be classified based on various

parameters as follows:

1. Based on Mode of Processing

2. Based on Number of Users

3. Based on Number of Processes

4. Based on Type of user Interface.


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Based on Mode of Processing

Two Classifications:

1. Batch processing OS

2. Real-time OS

Batch processing OS: The jobs to be executed are gathered for a

specific period of time called A Batch and

form a queue of programs.

The batch of programs are then taken up for

execution one by one in sequence.

Example:


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Based on Number of Users


1. Single user OS

2. Multi-user OS

Single User OS: This kind of OS runs one user work at a time

(i.e) only one program resides in computer

memory and remains there till it is executed. Example: MSDOS.


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Multi-user OS:

This type of OS enables more than one user to

work upon it.

They allow 2 or more users to run programs at

the same time.

Example: Windows NT, Unix, Linux.


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Multi-tasking OS:

It is the execution of 2 or more programs by an

user concurrently on the same computer withone CPU.

The OS handles each job for a determined

amount of time BUT ONE AT A TIME. Example: we may type text in MS-Word, while

giving some printout.


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Multi-programming OS:

It allows a number of programs to work

belonging to different users stored in the mainmemory at the same time & executed

concurrently.

The CPU spends certain amount of time

executing each users program.

It works so fast with all the programs & takes

care of switching the CPU among the various

user works.

For Multi-programming, large memories are

required together with fast secondary storage

devices


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Time Sharing OS:

It is the processing done by a single computer,

of tasks belonging to several users, accessingthe system from different locations in a

rotation manner.

This requires a communication network inplace connecting various users to the

computer.

The OS will attend first attend to the first userfor a fixed time and go to the next users and so

on.


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Multi-processing:

A multi-processor OS is similar to multi-

programming OS, except that there is more thanone processor.

A computer with 2 or more processors can run

more than one program at a given time byassigning them to different processors.


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Based on Type of user Interface.


1. CUI OS 2. GUI OS

CUI OS [ Character User Interface OS]:

This kind of OS interacts with the users only

through the commands typed from the

keyboard.

It does not support any other input device than

keyboard.

The user has to remember the syntax of

commands exactly.


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GUI OS:

The GUI OS makes use of icons (images or

pictures) to perform a task. It is a picture based way of interacting with the

computer.

This OS makes use of mouse for selecting andexecuting any task.

5 operating systems.ppt

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