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Factsheet: What is an Operating System?

We hear the term Operating System, or OS regularly - whether it is for a laptop running Windows or a smartphone, but what is an Operating System and why is it important?

Nowadays, Consumer/domestic computer operating systems come in three main variants.

  • Microsoft Windows
  • Mac OS
  • Linux [includes Android]

msdosRoll back to the 80's and 90's and you'd find DOS (Disc Operating System) installed, which was a text-based OS. There were various brands, such as IBM PC-DOS, DR-DOS, with Microsoft's MS DOS being the market leader due to a bundling deal they made with IBM.

At its most simple, a computer operating system is nothing more than a platform which is required for other programs to run on. It is instructed to load on computer start up by the Basic Input / Output System (abbreviated to BIOS in common usage).  A BIOS is the first instruction set given to the computer system to load on start up, and contains only the most basic instructions needed to start or 'boot' the computer up.  As part of its function it tests for errors before the more conventional (and much larger) operating system is located by it, loaded onto the system and takes over system management.

Conventionally, the BIOS needed to be as small as possible so that it was able to be stored in the memory contained on a single chip located on the system motherboard.  Each BIOS is custom written for the make and model of computer it runs on, to take account of the custom physical components used in the manufacture of that system.  It is stored in memory that is Read Only Memory (ROM) the contents of which are retained when the system is powered down.  The BIOS is designed to be read in its entirety and in a specific sequence.  It is not really designed to be modified by the user, although nowadays most can be updated by software if updates come out, as the data is stored in 'Flash memory'.

windows 1Today, most consumer operating systems utilize a Graphic User Interface (GUI), a mainly pictagraphic representation of  tasks and options available to the user designed to simplify the process of interacting with the Operating System as much as possible, as the Command Line Interface (a text based system of interacting with the computers operating instruction set) was found too be to complex for the average user.

Pictured right you can see a screenshot of Microsoft Windows 1.01 - a bit different from today's slick graphical interfaces.

In a multi tasking system (a system that can run more than one program or application at a time), the Operating System tells the computer which applications to run and the order that they should run in.  It is also responsible for allocating and sharing of the memory needed for the programs which run on it. It handles communication to and from attached hardware devices such as hard disks, printers, and the monitor, (screen), and in computers which utilize more than one processor (which is where all the computational calculative tasks are done in a computer) it is responsible for dividing the operations of a program so that it runs on those multiple processors.

The operating system is also responsible for messages sent to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred.

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