Processing time
The operating system (OS) makes it possible to run multiple programs at once. Several programs can be stored in RAMRandom access memory. This is volatile memory that is constantly being written to and read from. It does not retain its contents without a constant supply of power. When a computer is turned off, everything stored in its RAM is lost. at the same time, however only one program is processed by the CPU/processorCentral processing unit - the brain of the computer that processes program instructions. at any one time.
The OS controls which process is being executed by the CPU at any time and manages access to the CPU between programs. This allows a computer with a single processor to multitask. For example, you may be listening to an mp3 file while surfing websites on your PC. The job of working out when to swap processes is known as scheduling.
This swapping happens so fast, it appears all processes are running at the same time. If there are too many processes, or some of them are making the CPU work especially hard, it can seem as though programs are working very slowly or have stopped.
The OS is responsible for organising processing time between programs and users. This is achieved through the process of interrupt handlingAn interrupt handler prioritises the interrupts and saves them in a queue if more than one is waiting to be handled.
When a program is running, it will continue to do so until it has 'terminated' (or finished). This is no good if we move the mouse or press a key and want a different program to do something. Every time the mouse is moved or a key pressed an interrupt signal is generated. The operating system handles this and blocks the current process from running so that the new interrupt instruction can be processed.
Other features of typical operating systems include:
- Managing hardware - Communicating with peripheralA device that connects to a computer, eg a mouse, keyboard, printer or scanner. such as printers. Peripheral devices are input or output (I/O) devices. The OS will have device driverA piece of software which controls a peripheral device. that communicate directly with the hardware for these devices.
- Providing a user interface - A user interface provides the means to open applications, run them and shut them down. You may be familiar with Graphical User Interfaces (GUIs) such as those provided by Windows, iOS, OSX and Android. They use Windows, Icons, Menus and Pointers (WIMP) to instigate functionality.