Operating

SystemsBy the end of this session, you will know:

What an Operating System is.

The functions it performs.

Operating SystemsAn OS is a set of programs

that controls how the hardware of a computer works… It is the means of communication between the user and the computer, deals with the loading and running of application programs and manages the transfer of data and files to and from the peripheral devices.

What is it?

Operating SystemsUser

Applications Software

Operating System

Computer Hardware

The OS acts like a bridge between the applications software and the computer hardware.

Users need applications software to carry out tasks, the software needs the operating system in order to communicate with the hardware.

Operating Systems• Accepts data from input

devices and transfers it to the computer’s memory.

• Makes sure any output is sent to the correct output device.

• Manages the transfer of data between the computer’s memory and backing storage devices.

Functions:

Operating Systems• Allocates memory space

to programs and data.

• Loads applications software into memory and controls the running of them.

• Deals with any errors that occur when a program is being run and informs the user.

Functions:

Operating Systems• Provides a human

computer interface for the user

• Provides special facilities for multiprogramming.

• Manages system security by restricting access to prevent unauthorised access to the system.

Functions:

…So, the OS is quite important!

Operating Systems• Transferring data to a

printer?

• Allocating storage space on a disk?

• Positioning text in a word processing document?

• Finding a database record?

• Accepting keyboard input?

• Adding colour to a drawing on screen?

Question!

Which 3 of the

following is an OS

responsible for?

Operating SystemsA multiprogramming OS

holds more than one program in memory.

Multiprogramming:

There are 2 Types of Multiprogramming OS you need

to know : Multitasking and Multiuser

Operating Systems

A Multitasking OS allows two or more programs to run at the same time.

…It’s like having MS Word, iTunes and Solitaire open on your computer at the same time!

Multitasking:

Operating Systems

Multitasking is allowed as the OS swaps each program in and out of memory in turn when needed.

The program not being used is temporarily stored on the backing storage until needed again.

Multitasking:

Operating SystemsMultitasking:

CPUBacking Store

Program A (Not used)

Program B

(Just used)

Program C (Being used)

Operating Systems

A Multiuser OS allows many different users at different terminals (in a network) to share the processing time on a central computer.

Multiuser:

Operating Systems

This is allowed as the OS switches quickly between the terminals and giving each one a small amount of processing time on the central computer (called a time slice).

Multiuser:

Operating SystemsMultiuser:

Central Computer OS

Terminal 1

Terminal 2

Terminal 3

Terminal 4

Processing power will be given in a

‘round robin’ way!