Operating systems can be classified in several ways: - Single-user, single-processor systems have one user and CPU. Examples include MS-DOS. - Batch processing systems automatically execute jobs one after the other without user interference. A batch monitor controls the environment. - Multiprogramming systems increase efficiency by allowing multiple jobs to reside in memory at once. The CPU switches between jobs during I/O waits. - Time-sharing or multitasking systems further improve interaction by rapidly switching between jobs, giving the appearance that users interact with programs simultaneously.

1. Operating System 06
Operating System Classification
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Operating Systems
Classification
• The variations and differences in the nature of different
operating systems may give the impression that all operating
systems are absolutely different from each-other. But this is
not true.
• All operating systems contain the same components whose
functionalities are almost the same.
• For instance, all the operating systems perform the functions
of storage management, process management, protection of
users from one-another, etc.
• The procedures and methods that are used to perform these
functions might be different but the fundamental concepts
behind these techniques are just the same.
• Operating systems in general, perform similar functions but
may have distinguishing features.
• Therefore, they can be classified into different categories on
different bases.

3. Single User – Single
Processing System
• The simplest of all the computer systems is a single
use-single processor system.
• It has a single processor, runs a single program and
interacts with a single user at a time.
• The operating system for this system is very simple to
design and implement.
• However, the CPU is not utilized to its full potential,
because it sits idle for most of the time.
• In this configuration, all the computing resources are
available to the user all the time. Therefore, operating
system has very simple responsibility.
• A representative example of this category of operating
system is MS-DOS.

4. Single user – single processor system

5. Batch Processing Systems
• The main function of a batch processing system is to
automatically keep executing one job to the next job in the
batch.
• The main idea behind a batch processing system is to
reduce the interference of the operator during the processing
or execution of jobs by the computer.
• All functions of a batch processing system are carried out by
the batch monitor. The batch monitor permanently resides in
the low end of the main store.
• The current jobs out of the whole batch are executed in the
remaining storage area.
• In other words, a batch monitor is responsible for controlling
all the environment of the system operation.
• The batch monitor accepts batch initiation commands from the
operator, processes a job, performs the job of job termination
and batch termination.

6. Batch processing system

7. Multiprogramming Operating
System
• The objective of a multiprogramming operating system is to increase
the system utilization efficiency.
• The batch processing system tries to reduce the CPU idle time
through operator interaction. However, it cannot reduce the idle time
due to IO operations.
• So, when some IO is being performed by the currently executing job
of a batch, the CPU sits idle without any work to do.
• Thus, the multiprogramming operating system tries to eliminate such
idle times by providing multiple computational tasks for the CPU to
perform.
• This is achieved by keeping multiple jobs in the main store.
• So, when the job that is being currently executed on the CPU needs
some IO, the CPU passes its requirement over to the IO processor.
• Till the time the IO operation is being carried out, the CPU is free
to carry out some other job.

8. Time Sharing or Multitasking
System
• Time sharing, or multitasking, is a logical
extension of multiprogramming.
• Multiple jobs are executed by the CPU
switching between them, but the switches
occur so frequently that the users may
interact with each program while it is running.
• An interactive, or hands-on, computer system
provides on-line communication between the
user and the system.
• The user gives instructions to the operating
system or to a program directly, and receives
an immediate response.

9. Parallel Systems
• Most systems to date are single-processor systems; that
is, they have only one main CPU. However, there is a
trend toward multiprocessor systems.
• Such systems have more than one processor in close
communication, sharing the computer bus, the clock,
and sometimes memory and peripheral devices.
• These systems are referred to as tightly coupled
systems.
• There are several reasons for building such systems
such as increased throughput, lower cost, increased
reliability, fault tolerance.
• The Tandem system uses both hardware and software
duplication to ensure continued operation despite faults
• Distributed Systems

10. Parallel Systems
• A recent trend in computer systems is to distribute
computation among several processors.
• In contrast to the tightly coupled systems, the processors do
not share memory or a clock.
• Instead, each processor has its own memory and clock.
• The processors communicate with one another through
various communication lines
• These systems are usually referred to as loosely coupled
systems, or distributed systems.
• The processors in a distributed system may vary in size and
function.
• They may include small microprocessors, workstations,
minicomputers, and large general-purpose computer systems.
• These processors are referred to by a number of different
names, such as sites, nodes, computers, and so on,
depending on the context in which they are mentioned.

11. Distributed systems
These systems are designed for achieving:
• Resource sharing.
• Computation speedup.
• Reliability.
• Communication.

12. Real Time Systems
• Another form of a special-purpose operating system is
the real-time system.
• A real-time system is used when there are rigid time
requirements on the operation of a processor or the
flow of data, and thus is often used as a control device
in a dedicated application.
• Sensors bring data to the computer. The computer must
analyze the data and possibly adjust controls to modify
the sensor inputs.
• Systems that control scientific experiments, medical
imaging systems, industrial control systems, and some
display systems are real-time systems.
• Also included are some automobile-engine fuel-injection
systems, home-appliance controllers, and weapon
systems.

13. Soft Real Time Systems
• A less restrictive type of real-time
system is a soft real-time system,
where a critical real-time task gets
priority over other tasks, and retains
that priority until it completes.

14. Assignment
• Briefly discuss the classification of Operating
Systems