Operating system

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Ubuntu GNU+Linux, a free operating system

An operating system (also called an OS) is a piece of software that is needed to run the programs on a computer or a mobile device. The programs that run on an operating system talk to the hardware.

Common families of operating systems

An operating system must be made up of different parts: (these can change depending on the operating system)

Tasks commonly done by operating systems

  • Interaction with the user, and management of attached devices (such as USB flash drives)
  • Management of programs (things like starting and stopping them)
  • Management of resources like processor time: Making sure each program gets a fair amount of power.
  • The reading and writing of data
  • Memory management: virtual memory, paging, swapping

What an operating system does

Most ordinary computer users take their operating system for granted. The easiest way to understand what an operating system does is to take a close look at what computers were like before operating systems were invented.

The earliest electronic computers did not have any operating system. If the user wanted to change what the computer was doing, the user had to open the back panel on the (then very large) computer, and change how the wires were connected. Changing what the computer did was very time consuming and required an expert.

Later, computer scientists decided to have the wires stay as they were, and feed instructions to the computer with punched cards (cards with holes that represented instructions) or magnetic tape. The computer would store the instructions in some kind of memory. This way of operating a computer is called the von Neumann architecture.

Still, computers of the time generally only had enough memory to "remember" one program at a time. If the user wanted the computer to run a different program, the user had to wipe out the first program from memory and then load another program into memory.

Computer operators and computer scientists grew tired of carrying around large stacks of punch cards. They also wanted computers to run more than one program at a time. As years of work changed or replaced computers to have more memory, computer operators and computer scientists decided that some computers could hold several programs in its memory. The computer user could then simply choose which program the user wanted to run. Running a computer this way requires a "boss" program that controls all the other programs, and asks the user what program the user wants to run. Such a boss program is called an operating system.

Having several programs in memory that can be run at any time makes some new problems. The operating system itself has to remember where the programs are at in memory. The operating system also has to prevent two programs from fighting over which one gets to use the processor.

Modern desktop or laptop computers need an operating system so that they can operate. They are usually sold with it already installed. Operating systems normally start up automatically when the user turns on the computer.


Operating systems can also have other differences:

  • Some are real-time systems.
  • Some are distributed systems.
  • Most use a GUI, some use a text-based interface.

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