Interrupts

In short: An interrupt is a signal with which hardware or software interrupts the processor so that it immediately handles an urgent event.

In more detail: Instead of constantly asking whether a key was pressed (polling), the keyboard reports via interrupt. The processor saves its state, runs the responsible handler and then returns to the interrupted work.

In Depth

• Hardware interrupts: Keyboard, network card, timer, storage.
• Software interrupts/traps: System calls and faults such as division by zero or page faults.
• Interrupt vector: A table says which routine belongs to which number.
• Keep it short: The handler should be quick. Heavy work is deferred (bottom half).
• Timer interrupt: Drives the operating system and enables time slices for multitasking.

See also: Process scheduling