An interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution. An interrupt is a line that links the peripheral to the processor. An interrupt is a hardware interrupt when it is requested by one of the PC's hardware components. For example, this is the case when a key is touched and the keyboard wants to get the processor's attention for this event.
Interrupt-controlled I/O reduces the severity of the two problems mentioned for program-controlled I/O by allowing the I/O device itself to initiate the device service routine in the processor. This is accomplished by having the I/O device generate an interrupt signal which is tested directly by the hardware of the CPU. When the interrupt input to the CPU is found to be active, the CPU itself initiates a subprogram call to somewhere in the memory of the processor; the particular address to which the processor branches on an interrupt depends on the interrupt facilities available in the processor.
Interrupt-controlled I/O reduces the severity of the two problems mentioned for program-controlled I/O by allowing the I/O device itself to initiate the device service routine in the processor. This is accomplished by having the I/O device generate an interrupt signal which is tested directly by the hardware of the CPU. When the interrupt input to the CPU is found to be active, the CPU itself initiates a subprogram call to somewhere in the memory of the processor; the particular address to which the processor branches on an interrupt depends on the interrupt facilities available in the processor.
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