A final specification to check while shopping for a scanner is the unit's speed. How much the speed of a scanner matters depends on how many times you intend to use it. Those scanning once or twice a day will certainly be less bothered by a slow scanner than those who are constantly acquiring images.

Unfortunately, evaluating scanning speed is difficult, because there is no single standard for evaluating the time it takes to complete a scanning operation. Manufacturers frequently specify the raw speed of their scanner motors (this number is usually expressed in milliseconds per line, or ms/ln), but that speed rarely correlates with real-world performance. Other considerations, including the speed of the scanner's driver software, the size of its memory cache, and the type of connection between it and the computer all weigh in on overall performance. It's also generally true that scanners take longer when scanning at higher resolutions, or when applying filters to an image during the scanning process.

The best way to evaluate a scanner's speed is to try out a few sample scans. Short of that, look for real-world comparisons in magazine reviews. These evaluations usually submit each scanner under consideration to the same scanning process, which results in fairly useful comparisons. Even when using these comparisons, though, be sure to factor in the way you will be using the scanner.