iGCSE Computer Science - Distance Learning

Tutor Marked Assignment 6
Tutor Marked Assignment 8 (Programming)

The Need for Interrupts

An interrupt is a way for the computer system to pause the instruction that it is currently processing in order to process a more important instruction. One of the main tasks of the operating system is to identify which instruction needs to be sent to the CPU next. This is done in order of priority, with any task that is linked to input or output being one of the highest priorities.


An interrupt may be created because the user has input something into the computer and the computer makes this a priority to appear to the user that there is no delay in processing. When a user notices that there is a delay between sending and receiving data, this is referred to as lag. In order to reduce this, the computer system creates priority tasks which may cause an interrupt when other tasks are running in the background.

There are a number of other reasons why an interrupt may occur within the computer system. One well-known reason is when a document is being printed:


A printer may send an interrupt to:

  • confirm that it is ready to receive more data
  • notify that it has run out of paper/ink
  • notify that an error has occurred (paper jam)
  • confirm that it has completed printing