Operating System

In order to operate computer, besides hardware and software we need something special, which can allow computer users to interact with computer is called as "operating system". In other terms, we can say that an operating system is a broker that acts as an intermidiatry between user of the computer  and the hardware.
The operating syatem as a disk manager performs following activities :
* Free space management
* Stroage allocation
* Disk scheduling
* Storage deallocation

There are many type of operating system:-


1. Batch operating system
2. Multi programming system
3. Time sharing system
4. Real time operating system
5. Multi processor operating system
6. Distributed Operating system

Batch operating system : -

This form of operating system was used in the earlier age. This system was developed when magnetic tapes were used for loading and unloading of the program. In this operating system, the programs were executed in a sequential fashion in batches. Suppose we recieve  3 programs A, B and C where A is a FORTRAN program, B is a basic program and C is FORTRAN  program. Then, as a part of early system, there will be loading and unloading time for basic interpreter and running the object code and again there will be loading and unloading time for FORTRAN compiler and running of the object code etc.

Multiprogramming system : -

Initially only one program was under execution, But with the advent of new methods and spooling, it was possible to keep more than one program into the main memory. This resulted  into multi programming operating system. In this type of operating system, more than one program  will reside into main memory.
The multi programming system has problem related with debugging and also loading of software libraies in anticipation for user. This resulted into a new technology, called as time sharing system, which is logical extension of multi programming. Example of operating systems which support multi programming are UNIX,WINDOWS 98 etc.

Time sharing system : -

Multi programmed batch system provide an enviorment, where various system  resources (like CPU,memory,I/O devices) were effectively utilised. In this time sharing system, the time of cpu is shared between multiple programs residing in the main memory. multiple jobs are executed by the CPU, switching between them, but the switch occurs so frequently that the user may not interact with other programs simultaneously while it is running. Example of time sharing operating system are multics,cal,UNIX etc.

Real time operating system : -

Real time operating system is a special purpose operating system designed for rigid time requirments on the operation of the processor or flow of data. real time operating system has well defined fixed time constraints.
These type of operating systems are used in process Industry, where a delay in action may result into serious action. One of the simple examples is power plant, chemical industry etc. Example is TOSDIC of toshiba system.`.


Multiprocessor operating system : -

As the name indicates, this is an operating system  where more than one process is active at atime. For a multi-processing system, multi programming is very essential. Multi Processing system can be symmetric or asymmetric. If it is a symmetric multi processing, then each processor run on same operating system, whereas in case of asymmetric multi processing, each processor is assigned a specific task and thus operating system may differ.

Distributed system : -

Here, each processor has it's own local memory and clock, communicate to other processor through communication each processor lines, such as high speed buses ,telephone line, VSAT etc. That is why sometime distributed system are also called as loosely coupled system. The main reasons for building of distributed system are computation speed up, Resource sharing, Reliability etc.