Transcript Slide 1

Operating
Systems
By the end of this session,
you will know:
What an Operating System is.
The functions it performs.
Operating Systems
What is
it?
An 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.
Operating Systems
User
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
Functions:
• 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.
Operating Systems
Functions:
• 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.
Operating Systems
Functions:
• 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.
…So, the OS is quite important!
Operating Systems
Question!
• Transferring data to a printer?
Which 3 of
the following
is an OS
responsible
for?
• 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?
Operating Systems
Multiprogramming:
A multiprogramming OS holds
more than one program in memory.
There are 2 Types of
Multiprogramming OS you need to
know : Multitasking and
Multiuser
Operating Systems
Multitasking:
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!
Operating Systems
Multitasking:
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.
Operating Systems
Multitasking:
CPU
Backing Store
Program A
(Not used)
Program C
(Being used)
Program B
(Just used)
Operating Systems
Multiuser:
A Multiuser OS allows many
different users at different terminals
(in a network) to share the
processing time on a central
computer.
Operating Systems
Multiuser:
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).
Operating Systems
Multiuser:
Terminal
2
Terminal
1
Central Computer
OS
Terminal
4
Terminal
3
Processing power will
be given in a ‘round
robin’ way!