MARCH 1991

No matter what the capacity of your hard disk drive, sooner or later you will run out of space. But before you go out and buy a larger drive, consider two alternatives: higher-density storage and compression.

* Higher-density storage is the simplest and best solution for increasing the capacity of your hard disk drive. Replacement hard disk controller boards for IBM PCs and compatibles are available from Perstor Systems Inc. ($199 to $275; 602-894-3494). These can increase the capacity of common hard disk drives by about 80%. And unlike compression products, a hard disk drive controller board does not take up precious RAM memory.

* Compression analyzes a file's contents and codes for recurring patterns -- the word the might be replaced by a 1, for example. Compression can increase your disk drive's capacity by about 80%. If the compression is done purely by software, the process takes longer every time you save a file -- and more time later to expand the file for use. But by adding a specialized accessory hardware board to your computer, compression can be performed far more quickly.

Although many programs can do compression, only a few do compression invisibly so the computer appears to operate normally. On IBM PCs and compatibles, Stac Electronics (619-431-7474) offers Stacker Coprocessor Hardware ($229) and Stacker Software ($149), a software system for laptops and other models that can't accept hardware accessories. For the Macintosh, the DoubleUp hardware compression ($229 from Sigma Designs Inc.; 415-770-0100) works on Mac II models. It uses a software interface called DiskDoubler, which is also available separately for software compression on recent Mac models ($79 from Salient Software, 415-321-5375).

-- Cary Lu