Hardware Interrupts
William Johnston Buchanan · 1998
Computer systems either use polling or interrupt-driven software to service external equipment. With polling the computer continually monitors a status line and waits for it to become active. While an interrupt-driven device sends an interrupt request to the computer, which is then serviced by an interrupt service routine (ISR). Interrupt-driven devices are normally better in that the computer is thus free to do other things while polling slows the system down as it must continually monitor the external device. Polling can also cause problems in that a device may be ready to send data and the computer is not watching the status line at that point. Figure 18.1 illustrates polling and interrupt-driven devices.