A disadvantage of conditional programmed I/O is the microcomputer needs to check the status bit by waiting in a loop. This type of I/O transfer is dependent on the speed of the external device. For a slow device this waiting may slow down the capability of the microprocessor to process other data. The polled I/O and interrupt I/O techniques are efficient in this type of situation.
Interrupt I/O is a device initiated I/O transfer. The external device is connected to a pin called the interrupt pin on the microprocessor chip, when the device needs an I/O transfer with the microcomputer, it activates the interrupt pin of the microprocessor chip. The microcomputer usually completes the current instructions and saves at least the contents of the current program counter on the stack.
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