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Operating System

Notes The Figure 2.1 depicts the role of the operating system in coordinating all the functions.

Figure 2.1: Functions Coordinated by the Operating System

I/O
Management
Protection & File
Security Management

Process Secondary
Management Storage
Management
Operating System

Communication
Management Memory
User Management
Interface Networking

2.2 Types of Operating System

Modern computer operating systems may be classified into three groups, which are distinguished
by the nature of interaction that takes place between the computer user and his or her program
during its processing. The three groups are called batch, time-sharing and real-time operating
systems.

Batch Processing Operating System

In a batch processing operating system environment users submit jobs to a central place where
these jobs are collected into a batch, and subsequently placed on an input queue at the computer
where they will be run. In this case, the user has no interaction with the job during its processing,
and the computer’s response time is the turnaround time the time from submission of the job
until execution is complete, and the results are ready for return to the person who submitted the
job.

Time Sharing

Another mode for delivering computing services is provided by time sharing operating
systems. In this environment a computer provides computing services to several or many users
concurrently on-line. Here, the various users are sharing the central processor, the memory, and
other resources of the computer system in a manner facilitated, controlled, and monitored by the
operating system. The user, in this environment, has nearly full interaction with the program
during its execution, and the computer’s response time may be expected to be no more than a
few second.

Real-time Operating System (RTOS)

The third class is the real time operating systems, which are designed to service those applications
where response time is of the essence in order to prevent error, misrepresentation or even disaster.
Examples of real time operating systems are those which handle airlines reservations, machine
tool control, and monitoring of a nuclear power station. The systems, in this case, are designed to
be interrupted by external signals that require the immediate attention of the computer system.

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