An operating system is a program that
manages the computer hardware. It also provides a basis for application
programs and acts as an intermediary between the computer user and the computer
hardware. The purpose of an operating system is to provide an environment in
which a user can execute programs in a convenient and efficient manner.
Def:
An operating system acts as an interface between the user and the
hardware.
The operating system must ensure the
correct operation of the computer system. The operating system provides certain
services to programs and to the users of those programs in order to make the
programming task easier. The specific services provided will, of course, differ
from one operating system to another but there are some common classes of
services that we identify and explore.
What
operating systems do?
An operating system is an important part
of almost every computer system. A computer can be divided into four
components:-
·
The Hardware
·
The operating system
·
The application programs, and
·
The users
Fig 14: Abstract view of components of computer system
Objectives
of Operating System
There are three main objectives of
operating system:
1.
Making a computer system convenient to
use
2.
Managing the system resources
3.
Controlling the computer processes
Making a computer system convenient to
use
·
An operating system is a layer of
software on top of the bare hardware of a computer system, which manages all
parts of the system, presents to the user with an interface or virtual machine,
which is easier to program and use. That is, the operating system hides the
details of the hardware resources from the programmer with a convenient
interface
·
It acts as an intermediary between the
hardware and it’s user, providing a high level interface to low level hardware
resources, and making it easier for the programmer and other users to access
and use those resources.
· The operating system layer hides the
details of the hardware from the programmer with a convenient interface for
using the system.
Managing the system resources
·
The second important objective of an
operating system is to manage the various resources of the computer system.
· This involves performing tasks such as –
keeping track of who is using which resource, granting resource request,
accounting resource usage and mediating conflicting requests from different
programs and users.
· The efficient and fair sharing of
resources among users and/or programs is a key goal of most operating systems.
· An operating system is a resource allocator. A computer system
has many resources (hardware and software) that may be required to solve a
problem: CPU time, memory space, file storage space, I/O devices and so on.
Controlling the computer processes
·
An operating system is a control system. A control program controls the
execution of user programs to prevent errors and improper use of computer.
·
It is especially concerned with the
operation and control of I/O devices.
Functions
of Operating System
The main functions of an operating
system are as follows:-
1.
Booting the Computer
The process of starting or restarting
the computer is known as booting. A cold boot is when you turn on a computer
that has been turned off completely. A warm boot is the process of using the
operating system to restart the computer.
2.
Provides a User Interface
A user interacts with software through
the user interface. The two main types of user interfaces are: command line and
a graphical user interface (GUI). With a command line interface, the user
interacts with the operating system by typing commands to perform specific
tasks. With a graphical user interface, the user interacts with the operating
system by using a mouse to access windows, icons, and menus.
3.
Process management
CPU can perform one task at one time. If
there are many tasks, operating system decides which task should get the CPU.
4. Memory management
It is also an
important function of operating system. The memory cannot be managed without
operating system. Different programs and data execute in memory at one time. If
there is no operating system, the programs may mix with each other. The system
will not work properly.
5. File management
The operating
system also handles the organization and tracking of files and directories
(folders) saved or retrieved from a computer disk. The file management system
allows the user to perform such tasks as creating files and directories,
renaming files, coping and moving files, and deleting files.
6. I/O management
Operating system
also controls all devices attached to computer. The hardware devices are
controlled with the help of small software called device drivers
7. Protection and security
Data is an
important part of computer system. The operating system protects the data
stored on the computer from illegal use, modification or deletion.
Protection
must be available to ensure that besides
the file, memory segments, CPU and other resources can be operated on by only
those process that have gained proper authorization from operating system.
Types
of Operating System:
1. Batch
operating system
2. Single
user single tasking operating system
3. Single
user multitasking operating system
4. Multi
–user multi tasking operating system
5. Real
time operating system
Batch operating system
· This is the earliest operating system,
where only one program is allowed to run at one time.
· We cannot modify any data used by the
program while it is being run. If an error is encountered, it means starting
the program from scratch all over again.
· Example:
MS-DOS
Single user single tasking operating
system
· An operating system that allows a single
user to perform just one task at a time is a single user single tasking
operating system.
· This type of operating systems are
useful because, it takes less memory and don’t require expensive computers.
· Example:
MS-DOS,
the palmtop OS (used in palmtops).
Single user multi-tasking operating
system
· A single user multi-tasking operating
system is one that allows a single user to perform two or more functions at
one.
· Example:
MS-Windows,
Macintosh Operating system.
Multi –user multi-tasking operating
system
· A multi-user multi-tasking operating
system is an operating system that allows multiple users to use programs that
are simultaneously running on a single network server called a terminal server.
· This type of operating system provides
each user a complete environment, called a user session, on the server. Each
user’s application runs within their user session on the server separate from
all other user sessions. The software that makes this possible is called terminal
client.
· Example:
UNIX,
MVS (Mainframe OS).
Real Time Operating system
· A real time operating system is a very
fast, relatively small OS, when they are built into the circuitry of the device
and are not loaded from a disk drive.
· A real time operating system is needed
to run real time applications; it may support multiple simultaneous task, or it
may only support single tasking.
· A real time application is an
application that responds to certain inputs extremely quickly (thousandths or
millionths of a second). Real time applications are needed to run medical
diagnostics equipment, life support systems, scientific instruments etc.
· Example:
Lynx OS, RT Linux, Windows CE
