Buyers' Guide to Hard Drives

Key Features

Capacity: Today's PC hard drives have at least 20GB of space--about four times the amount you'll need for an operating system, applications, and several years' worth of e-mail messages and documents. The remaining 15GB can hold about 12,000 good-quality, 3-megapixel digital photos or 3750 4-minute MP3 songs encoded at 128 kbps. Capacity really matters for graphic designers and people who edit (or simply archive) video. For example, the contents of a 1-hour MiniDV camcorder tape consume 13GB.

If you want high capacity, remember that PCs usually have room for two hard drives. You may save money by purchasing, say, two 80GB drives instead of a single 160GB unit that sells for a premium.

Rotational speed: Current ATA hard drives spin their disks at either 5400 or 7200 revolutions per minute. Usually, but not always, the 7200-rpm drives retrieve data faster. For example, in our tests, the 80GB, 5400-rpm Maxtor DiamondMax D540X copied a 1.2GB file 33 percent faster than the 80GB, 7200-rpm Seagate Barracuda ATA IV. Sometimes other factors, such as the algorithms drives use to retrieve data, can affect performance.

Interface: Nearly all desktop PC drives use the parallel ATA interface, supporting maximum transfer rates of either 100 or 133 megabytes per second. But hard drives can't sustain transfer rates fast enough to utilize the extra bandwidth (though they can push out short bursts of data at 100 MBps or greater). And most motherboards don't support ATA/133, so you'll need an add-in card to use it. Fortunately, ATA/133 drives also work with ATA/100 and earlier interfaces.

Buffer: When a system requests data, a hard drive doesn't simply fetch what is requested; it also loads its buffer memory with additional information that the processor is likely to ask for next. We've found that drives with an 8MB buffer tend to perform better on our disk-intensive Photoshop and file-search tests.