Mitsubishi Electric Apricot XEN pentium, Owner'S Handbook Manual

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XEN OWNER'S HANDBOOK A/5
Inside your computer
Appendix A
Interrupts (IRQ)
Your computer (like every other ISA compatible PC) supports
15 (IRQ) hardware interrupts. These interrupts are used to
alert the processor that a peripheral (e.g. the keyboard
controller, or an expansion card) requires a particular piece
of software to be executed. This piece of software is known
as an interrupt service routine.
Each peripheral has a unique interrupt service routine that is
executed in response to the interrupt assigned to that
peripheral.
When an interrupt occurs, the processor stops executing its
current task, executes the interrupt service routine, then
returns to its original task. The processor is, literally,
interrupted.
A hardware interrupt may be referred to as an IRQ. This is
because the motherboard signals used to generate the
interrupts are labelled IRQx where x is a number between 0
and 15, excluding 2.
Some interrupts are assigned to standard functions and are
essential for the operation of the board. Examples of these
are, IRQ0 which is used to maintain the system time, and
IRQ13 which is used by the coprocessor.