1.2 INTRODUCTION TO OPERATING SYSTEM

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