What is an interrupt? With an ex, illustrate the concept of interrupt.

INTERRUPTS - 

• I/O device initiates the action instead of the processor. This is done by sending a special hardware signal to the processor called as interrupt(INTR), on the interrupt-request line.

• The processor can be performing its own task without the need to continuously check the I/O device.

• When device gets ready, it will "alert" the processor by sending an interrupt-signal (Figure 4.5).

• The routine executed in response to an interrupt-request is called ISR(Interrupt Service Routine).

• Once the interrupt-request signal comes from the device, the processor has to inform the device that its request has been recognized and will be serviced soon. This is indicated by a special control signal on the bus called interrupt-acknowledge(INTA).

For example, pressing a keyboard key or moving a mouse plugged into a PS/2 port triggers hardware interrupts that cause the processor to read the keystroke or mouse position. Hardware interrupts can arrive asynchronously with respect to the processor clock, and at any time during instruction execution.