Polling: A technique whereby an I/O device controller checks for device availability periodically instead of using interrupts to trigger processing. In general interrupts are used where input timing is unpredictable, polling can be used for predictable operations. But much is a matter of tradition and convention. For example, serial I/O is generally interrupt driven, but parallel I/O is very often polled.

The principle advantage of polling is that it can achieve very high throughputs if the entire machine is dedicated to one job. The disadvantage is the difficulty or impossibility of handling operations whose sequencing is not predictable.

The choice of polling vs interrupting is sometimes has little relationship to the theoretical merits of either. For example, use of polling is a standard cure for slow printing in Novell systems, but that appears to have more to do with tolerance for incorrect hardware setups than any actual advantages of polling.

Return To Index Copyright 1994-2002 by Donald Kenney.