Prepared by Dr. Subhendu Kumar Rath, BPUT
What is an Operating System?
A program that acts as an intermediary between a user of a computer and the computer hardware.
An operating System is a collection of system programs that together control the operations of a computer
Some examples of operating systems are UNIX, Mach, MS-DOS, MS-Windows, Windows/NT, Chicago, OS/2,
MacOS, VMS, MVS, and VM.
Operating system goals:
Execute user programs and make solving user problems easier.
Make the computer system convenient to use.
Use the computer hardware in an efficient manner.
Computer System Components
1. Hardware – provides basic computing resources (CPU, memory, I/O devices).
2. Operating system – controls and coordinates the use of the hardware among the various application
programs for the various users.
3. Applications programs – Define the ways in which the system resources are used to solve the computing
problems of the users (compilers, database systems, video games, business programs).
4. Users (people, machines, other computers).
Abstract View of System Components
Operating System Definitions
Resource allocator – manages and allocates resources.
Control program – controls the execution of user programs and operations of I/O devices .
Kernel – The one program running at all times (all else being application programs).
Components of OS: OS has two parts. (1)Kernel.(2)Shell.
(1)Kernel is an active part of an OS i.e., it is the part of OS running at all times. It is a programs which
can interact with the hardware. Ex: Device driver, dll files, system files etc.
(2) Shell is called as the command interpreter. It is a set of programs used to interact with the application
programs. It is responsible for execution of instructions given to OS (called commands).
Operating systems can be explored from two viewpoints: the user and the system.
User View: From the user’s point view, the OS is designed for one user to monopolize its resources, to
maximize the work that the user is performing and for ease of use.
System View: From the computer's point of view, an operating system is a control program that manages the
execution of user programs to prevent errors and improper use of the computer. It is concerned with the
operation and control of I/O devices.