1. What is an operating system? Explain the six types of operating systems.
Ans: An ‘operating system’ (OS) is a collection of system programs that together control the
operation of a computer system. The OS along with hardware, application and other system softwares
and users constitute a computer system. It is the most important part of any computer system. It acts as
an intermediary between a user and the computer hardware. The OS has evolved immensely from its
primitive days to the present digital era. From batch processing systems to the latest embedded systems,
the OS can be classified into six broad categories that are described as follows:
• Batch processing OS: This type of OS was one of the first to evolve. It allowed only one program
to run at a time. These kinds of OS can still be found on some mainframe computers running
batches of jobs. It works on a series of programs that are held in a queue. The OS is responsible for
scheduling the jobs according to priority and the resources required. These are good at churning
through large numbers of repetitive jobs on large computers. For example, this OS would be best
suited for a company wishing to automate their payrolls. A list of employees will be entered, their
monthly salaries will be calculated, and corresponding pay slips would be printed. Batch process-
ing is useful for this purpose, since these procedures are to be repeated for every employee and
• Multi-user or time-sharing OS: This system is used in computer networks that allow different
users to access the same data and application programs on the same network. It builds a user data-
base account, which defines the rights that users can have on a particular resource of the system.
Some of the common examples of multi-user OS include Windows XP and Linux.
• Multi-programming or multi-tasking OS: In this system, more than one process can be executed
concurrently. The processor is switched rapidly between the processes. Hence, a user can have
more than one process running at a time. For example, a user on his/her computer can have a word
processor and an audio CD player running at the same time. It allows the user to switch between
the running applications and even transfer data between them. That is, a user can copy a picture
from an Internet opened in the browser application and paste it into an image editing application.
• Real-time OS (RTOS): This system is designed to respond to an event within a pre-determined
time. This kind of OS is primarily used in process control, telecommunications, and so on. The
OS monitors various inputs that affect the execution of processes, changing the computers model
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