Types of Operating System
Batch operating system
Time-sharing operating
systems
Distributed operating
System
Network operating
System
Real Time operating
System
Hard real-time systems
Soft real-time systems
Operating
systems are there from the very first computer generation and they keep
evolving with time. In this chapter, we will discuss some of the important
types of operating systems which are most commonly used.
Batch operating system
The users of a batch operating system do not interact with the
computer directly. Each user prepares his job on an off-line device like punch
cards and submits it to the computer operator. To speed up processing, jobs
with similar needs are batched together and run as a group. The programmers
leave their programs with the operator and the operator then sorts the programs
with similar requirements into batches.
The problems with Batch Systems are as follows −
- Lack of
interaction between the user and the job.
- CPU is often
idle, because the speed of the mechanical I/O devices is slower than the
CPU.
- Difficult to
provide the desired priority.
Time-sharing operating
systems
Time-sharing is a technique which enables many people, located
at various terminals, to use a particular computer system at the same time.
Time-sharing or multitasking is a logical extension of multiprogramming.
Processor's time which is shared among multiple users simultaneously is termed
as time-sharing.
The main difference between Multiprogrammed Batch Systems and
Time-Sharing Systems is that in case of Multiprogrammed batch systems, the
objective is to maximize processor use, whereas in Time-Sharing Systems, the
objective is to minimize response time.
Multiple jobs are executed by the CPU by switching between them,
but the switches occur so frequently. Thus, the user can receive an immediate
response. For example, in a transaction processing, the processor executes each
user program in a short burst or quantum of computation. That is, if n users
are present, then each user can get a time quantum. When the user submits the
command, the response time is in few seconds at most.
The operating system uses CPU scheduling and multiprogramming to
provide each user with a small portion of a time. Computer systems that were
designed primarily as batch systems have been modified to time-sharing systems.
Advantages of Timesharing operating systems are as follows −
- Provides the
advantage of quick response.
- Avoids
duplication of software.
- Reduces CPU
idle time.
Disadvantages of Time-sharing operating systems are as follows −
- Problem of
reliability.
- Question of
security and integrity of user programs and data.
- Problem of
data communication.
Distributed operating
System
Distributed systems use multiple central processors to serve
multiple real-time applications and multiple users. Data processing jobs are
distributed among the processors accordingly.
The processors communicate with one another through various
communication lines (such as high-speed buses or telephone lines). These are
referred as loosely coupled systems or distributed systems.
Processors in a distributed system may vary in size and function. These
processors are referred as sites, nodes, computers, and so on.
The advantages of distributed systems are as follows −
- With resource
sharing facility, a user at one site may be able to use the resources
available at another.
- Speedup the
exchange of data with one another via electronic mail.
- If one site
fails in a distributed system, the remaining sites can potentially
continue operating.
- Better service
to the customers.
- Reduction of
the load on the host computer.
- Reduction of
delays in data processing.
Network operating
System
A Network Operating System runs on a server and provides the
server the capability to manage data, users, groups, security, applications,
and other networking functions. The primary purpose of the network operating
system is to allow shared file and printer access among multiple computers in a
network, typically a local area network (LAN), a private network or to other
networks.
Examples of network operating systems include Microsoft Windows
Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell
NetWare, and BSD.
The advantages of network operating systems are as follows −
- Centralized
servers are highly stable.
- Security is
server managed.
- Upgrades to
new technologies and hardware can be easily integrated into the system.
- Remote access
to servers is possible from different locations and types of systems.
The disadvantages of network operating systems are as follows −
- High cost of
buying and running a server.
- Dependency on
a central location for most operations.
- Regular
maintenance and updates are required.
Real Time operating
System
A real-time system is defined as a data processing system in
which the time interval required to process and respond to inputs is so small
that it controls the environment. The time taken by the system to respond to an
input and display of required updated information is termed as the response
time. So in this method, the response time is very less as compared to online
processing.
Real-time systems are used when there are rigid time
requirements on the operation of a processor or the flow of data and real-time
systems can be used as a control device in a dedicated application. A real-time
operating system must have well-defined, fixed time constraints, otherwise the
system will fail. For example, Scientific experiments, medical imaging systems,
industrial control systems, weapon systems, robots, air traffic control
systems, etc.
There are two types of real-time operating systems.
Hard real-time systems
Hard real-time systems guarantee that critical tasks complete on
time. In hard real-time systems, secondary storage is limited or missing and
the data is stored in ROM. In these systems, virtual memory is almost never
found.
Soft real-time systems
Soft real-time systems are less restrictive. A critical
real-time task gets priority over other tasks and retains the priority until it
completes. Soft real-time systems have limited utility than hard real-time
systems. For example, multimedia, virtual reality, Advanced Scientific Projects
like undersea exploration and planetary rovers, etc.
