< Operating Systems

Concepts

1) What is an operating system?

An operating system is the 'brains' behind the computer to extend the functionality of the machine and to manage all the resources allocated to it.

2) The history of operating systems

The are several 'generations' of operating systems. It was not until after World War II that progress was made to construct digital computers. This was known as the First Generation (1945-1955) of computers, involving large vacuum tubes and plugboards.

The Second Generation (1955-65) saw transistors being used and programmers would run 'jobs' (sets of programs) using punch cards. As costs of computer use was high, programmers looked for ways to reduce wasting time using them, and thus the solution was to use a 'batch system' whereby a number of jobs would be collected together and fed into the computer as input.

The Third Generation (1965-1980) had developed the technique of 'multiprogramming' meaning that several jobs could be kept in partitioned memory. This meant that while one job was waiting to complete, another job could use the CPU.

The Fourth Generation (1980 - Present) is with the invention of the PC or personal computer. Microprocessors were developed using chips. Disk operating systems became available. Networked and distributed operating systems began to develop.

3) Important concepts

Aside from the list below, it is important to understand such concepts as:
system call - set of extended instructions that the operating system provides to interface between the operating system internals and user programs
process - program execution in an operating system
file - place to hold data in a more permanent way than in memory
the shell - a command interpreter that allows users to execute programs

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