OPERATING SYSTEM

Operating system is an integrated set of a program that is used to manage the various resources and overall operations of a computer system. Its prime objectives is to improve the performance and efficiency of a computer system and increase facility the ease with which a system can be used like manager of a company.

Operating systems run in an infinite loop, each time taking instructions in the form of commands or programs from the users and executing them. This loop continues until the user terminates the loop when the computer shuts down. This is one program that runs all the time, as long as the computer is operational and exits only when the computer is shut down.


TYPES OF OPERATING SYSTEM


1. Batch Processing Systems
2. Multiprogramming Operating system
3. Network Operating System
4. Distributed Operating System






BATCH OPERATING SYSTEM:-

A batch processing system, which serves collection of jobs, called a BACTH. It requires grouping of similar jobs, which consist of programs, data and system commands. They do this by sequentially reading the jobs into machine and then executing the programs for each job in the batch. Examples of such programs include Payroll, Forecasting etc. Users are not required to wait while the job is being processed. They can submit their programs to operators and return later to collect them. Just like, when the job requests the printer to output a line, that line is copied into system buffer and is written to the disk. When the job is completed, the output is actually printed. This form of processing is called SPOOLING.


MULTIPROGRAMMING OPERATING SYSTEM

In computer systems, there may be various jobs running simultaneously, and then the system must choose among them. In a multiprogramming operating system, the operating system simply switches to and executes another job. When that job needs to wait, the CPU is switched to another job, and so on. Eventually, the first job finishes waiting and gets the CPU back. As long as there is always some job tom execute, the CPU will never be idle. Multiprogramming operating systems increases CPU utilization by organizing jobs such that the CPU always has one to execute


Different forms of multiprogramming operating system are:-


 Multitasking operating system:- The concurrent operation by one Central Processing Unit of two or more processes. The ability to execute more than one task at the same time. In multitasking, only one CPU is involved, but switches from one program to another so quickly that it gives the appearance of the programs at the same time.

There are two basic types of multitasking:-

1. PREEMPTIVE and
2. COOPERATIVE.


 Multiprocessing Operating System:- Refers to a computer system’s ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently. UNIX is one of the most widely used multiprocessing systems. It also refers to the utilization of multiple CPU’s in a single computer system. This is also called Parallel Processing. Thus, it is a method of computing in which different parts of a task are distributed between two or more similar Central Processing Units, allowing the computer to complete operations more quickly and to handle larger, more complex procedures.


 Multi-threading Operating System:- Multi threading allows different parts of a single program to run concurrently. Multi threading is the ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.


 Time Sharing Operating System:- It is a form of multiprogrammed operating system, which operates, in an interactive mode with a quick response time. A time-sharing system allows many users to simultaneously share the computer resources. Since each action or command in a time-shared system take a very small fraction of time, only a little time is needed for each user.