Operating System
An Operating System (OS) is an
interface between a computer user and computer hardware. An operating system is
a software which performs all the basic tasks like file management, memory
management, process management, handling input and output, and controlling
peripheral devices such as disk drives and printers.
Some popular Operating Systems
include Linux Operating System, Windows Operating System, VMS, OS/400, AIX,
z/OS, etc.
Definition
An operating system is a program
that acts as an interface between the user and the computer hardware and
controls the execution of all kinds of programs.
Following are some of important
functions of an operating System.
- Memory Management
- Processor Management
- Device Management
- File Management
- Security
- Control over system performance
- Job accounting
- Error detecting aids
- Coordination between other software
and users
Type and Classification of OS
Some of the widely used
operating systems are as follows-
1. Batch Operating System –
This type of operating system does not interact with the computer directly.
There is an operator which takes similar jobs having same requirement and group
them into batches. It is the responsibility of operator to sort the jobs with
similar needs.
Advantages of Batch
Operating System:
·
It is very difficult to guess or know
the time required by any job to complete. Processors of the batch systems know
how long the job would be when it is in queue
·
Multiple users can share the batch
systems
·
The idle time for batch system is
very less
·
It is easy to manage large work
repeatedly in batch systems
Disadvantages of Batch
Operating System:
·
The computer operators should be well
known with batch systems
·
Batch systems are hard to debug
·
It is sometime costly
·
The other jobs will have to wait for
an unknown time if any job fails
Examples of Batch based
Operating System: Payroll System, Bank Statements
etc.
2. Time-Sharing Operating Systems –
Each task is given some time to execute, so that all the tasks work smoothly.
Each user gets time of CPU as they use single system. These systems are also
known as Multitasking Systems. The task can be from single user or from
different users also. The time that each task gets to execute is called
quantum. After this time interval is over OS switches over to next task.
Advantages of
Time-Sharing OS:
·
Each task gets an equal opportunity
·
Less chances of duplication of
software
·
CPU idle time can be reduced
Disadvantages of
Time-Sharing OS:
·
Reliability problem
·
One must have to take care of
security and integrity of user programs and data
·
Data communication problem
Examples of Time-Sharing
OSs are: Multics, Unix etc.
3. Distributed Operating System –
These types of operating system is a recent advancement in the world of
computer technology and are being widely accepted all-over the world and, that
too, with a great pace. Various autonomous interconnected computers communicate
each other using a shared communication network. Independent systems possess
their own memory unit and CPU. These are referred as loosely coupled
systems or distributed systems. These system’s processors differ in
size and function. The major benefit of working with these types of operating
system is that it is always possible that one user can access the files or
software which are not actually present on his system but on some other system
connected within this network i.e., remote access is enabled within the devices
connected in that network.
Advantages of Distributed
Operating System:
·
Failure of one will not affect the
other network communication, as all systems are independent from each other
·
Electronic mail increases the data
exchange speed
·
Since resources are being shared,
computation is highly fast and durable
·
Load on host computer reduces
·
These systems are easily scalable as
many systems can be easily added to the network
·
Delay in data processing reduces
Disadvantages of
Distributed Operating System:
·
Failure of the main network will stop
the entire communication
·
To establish distributed systems the
language which are used are not well defined yet
·
These types of systems are not
readily available as they are very expensive. Not only that the underlying
software is highly complex and not understood well yet
Examples of Distributed
Operating System are- LOCUS etc.
4. Network Operating
System –
These systems run on a server and provide the capability to manage data, users,
groups, security, applications, and other networking functions. These type of
operating systems allow shared access of files, printers, security,
applications, and other networking functions over a small private network. One
more important aspect of Network Operating Systems is that all the users are
well aware of the underlying configuration, of all other users within the
network, their individual connections etc. and that’s why these computers are
popularly known as tightly coupled systems.
Advantages of Network
Operating System:
·
Highly stable centralized servers
·
Security concerns are handled through
servers
·
New technologies and hardware
up-gradation are easily integrated to the system
·
Server access are possible remotely
from different locations and types of systems
Disadvantages of Network
Operating System:
·
Servers are costly
·
User has to depend on central
location for most operations
·
Maintenance and updates are required
regularly
Examples of Network
Operating System are: Microsoft Windows Server 2003,
Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD
etc.
5. Real-Time Operating
System –
These types of OSs serves the real-time systems. The time interval required to
process and respond to inputs is very small. This time interval is called response
time.
Real-time systems are used when there
are time requirements are very strict like missile systems, air traffic control
systems, robots etc.
Two types of Real-Time
Operating System which are as follows:
·
Hard Real-Time Systems:
These OSs are meant for the applications where time constraints are very strict
and even the shortest possible delay is not acceptable. These systems are built
for saving life like automatic parachutes or air bags which are required to be
readily available in case of any accident. Virtual memory is almost never found
in these systems.
·
Soft Real-Time Systems:
These OSs are for applications where for time-constraint is less strict.
Advantages of RTOS:
·
Maximum Consumption: Maximum utilization of devices and system,thus more output from all
the resources
·
Task Shifting: Time assigned for shifting tasks in these systems are very less.
For example in older systems it takes about 10 micro seconds in shifting one
task to another and in latest systems it takes 3 micro seconds.
·
Focus on Application: Focus on running applications and less importance to applications
which are in queue.
·
Real time operating system in
embedded system: Since size of programs are
small, RTOS can also be used in embedded systems like in transport and others.
·
Error Free: These types of systems are error free.
·
Memory Allocation: Memory allocation is best managed in these type of systems.
Disadvantages of RTOS:
·
Limited Tasks: Very few tasks run at the same time and their concentration is very
less on few applications to avoid errors.
·
Use heavy system resources: Sometimes the system resources are not so good and they are
expensive as well.
·
Complex Algorithms: The algorithms are very complex and difficult for the designer to
write on.
·
Device driver and interrupt signals: It needs specific device drivers and interrupt signals to response
earliest to interrupts.
·
Thread Priority: It is not good to set thread priority as these systems are very
less prone to switching tasks.
Examples of Real-Time
Operating Systems are: Scientific experiments, medical
imaging systems, industrial control systems, weapon systems, robots, air
traffic control systems, etc.
