An operating system (OS) is software that manages computer hardware resources and provides
common services for computer programs. The operating system is an essential component of the
system software in a computer system. Application programs usually require an operating system
to function.
Types of Operating System:
1. Real-time operating system
A real-time operating system is a multitasking operating system that aims at executing real-time
applications. The main objective of real-time operating systems is their quick and predictable
response to events. They have an event-driven or timesharing design and often aspects of both. An
event-driven system switches between tasks based on their priorities or external events while timesharing operating systems switch tasks based on clock interrupts.
2. Multi-user operating system
A multi-user operating system allows multiple users to access a computer system at the same time.
Time-sharing systems and Internet servers can be classified as multi-user systems as they enable
multiple-user access to a computer through the sharing of time. Single-user operating systems
have only one user but may allow multiple programs to run at the same time.
3. Multi-tasking and single-tasking Operating System
A multi-tasking operating system allows more than one program to be running at the same time,
from the point of view of human time scales. A single-tasking system has only one running
program.
4. Distributed Operating system
A distributed operating system manages a group of independent computers and makes them
appear to be a single computer. Distributed computations are carried out on more than one
machine. When computers in a group work in cooperation, they make a distributed system.
5. Batch Processing
Batch processing is the execution of a series of programs (“jobs”) on a computer without manual
intervention. Jobs are set up so they can be run to completion without human interaction A
program takes a set of data files as input, processes the data, and produces a set of output data
files.
6. Multiprogramming
Multiprogramming is a rudimentary form of parallel processing in which several programs are run
at the same time on a uniprocessor. Since there is only one processor, there can be no true
simultaneous execution of different programs. Instead, the operating system executes part of one
program, then part of another, and so on. To the user it appears that all programs are executing at
the same time.
7. Time Sharing OS
In computing, time-sharing is the sharing of a computing resource among many users by means of
multiprogramming and multi-tasking.

Third Generation Computers:
Advantages:
• These computers were cheaper as compared to second-generation computers.
• They were fast and reliable.
• Use of IC in the computer provides the small size of the computer.
• IC not only reduce the size of the computer but it also improves the performance of the
computer as compared to previous computers.
• This generation of computers has big storage capacity.
• Instead of punch cards, mouse and keyboard are used for input.
• They used an operating system for better resource management and used the concept of
time-sharing and multiple programming.
• These computers reduce the computational time from microseconds to nanoseconds.
Disadvantages:
• IC chips are difficult to maintain.
• The highly sophisticated technology required for the manufacturing of IC chips.
• Air conditioning is required.
Fourth Generation Computers:
Advantages:
• Fastest in computation and size get reduced as compared to the previous generation of
computer.
• Heat generated is negligible.
• Small in size as compared to previous generation computers.
• Less maintenance is required.
• All types of high-level language can be used in this type of computers.
Disadvantages:
• The Microprocessor design and fabrication are very complex.
• Air conditioning is required in many cases due to the presence of ICs.
• Advance technology is required to make the ICs