When a hardware device needs the CPU to do something—for instance, when the keyboard needs the CPU to process a keystroke after a key has been pressed—the device needs a way to get the CPU’s attention, and the CPU must know what to do once it turns its attention to the device. These interruptions to the CPU are called hardware interrupts, and the device initiates an interrupt by placing voltage on the designated IRQ (interrupt request) line assigned to it. This voltage on the line serves as a signal to the CPU that the device has a request that needs processing. Often, a hardware device that needs attention from the CPU is referred to as “needing servicing.” Interrupts initiate many processes that the CPU carries out, and these processes are said to be “interrupt-driven.”
TESTS MUST BE CONDUCTED TO VERIFY ALL SYSTEM SOFTWARE COMMUNICATES WITH HARDWARE AND OTHER APPLICATION SOFTWARE
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