STI and CLI
Hardware interrupts are ignored unless the 'I' flag in the status register is set. To set the 'I' flag, use the set 'I' command, STI. To clear the 'I' flag, use the clear 'I' command CLI.
Hardware interrupts can be trapped in the same way that software interrupts can.
Hardware interrupts are triggered, as needed by disk drives, printers, key presses, mouse movements and other hardware events.
This scheme makes processing more efficient. Without interrupts, the CPU would have to poll the hardware devices at regular time intervals to see if any processing was needed. This would happen whether or not processing was necessary. Interrupts can be assigned priorities such that a disk drive might take priority over a printer. It is up to the programmer to optimise all this for efficient processing. In the IBM compatible PC, low number interrupts have a higher priority than the higher numbers.
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