Two Ways to Cram More Data on a CD-ROM

Michael Nadeau

For a lot of commercial and corporate CD-ROM software developers, 660 MB just isn't enough. Once a rarity, multidisc packages are now becoming more common. Because each additional CD-ROM disc increases production and packaging costs, developers are seeking ways to get more data on a disc.

Until now, lossless compression utilities have not been available for CD-ROM drives because of incompatibilities between DOS and CD-ROM file systems. Two companies aim to change that. CD-ROM USA (Golden, CO, (303) 526-7600) has created a driver for Stac Electronics' Stacker that allows it to compress files written to the CD-ROM file format. EWB and Associates (Carlsbad, CA, (619) 930-0440) has announced a package comprising a number of compression schemes that ar e optimized for CD-ROM. Both companies claim to minimally double the amount of data that can be recorded on a disc.

CD-ROM USA's CRI-X2 Driver, which is available now, fools PCs into writing to the ISO-9660 file format that is standard for most CD-ROMs. The computer thinks that it is writing to a standard DOS FAT (file allocation table), but in reality it's writing to an image of the DOS FAT that the CRI-X2 Driver creates in virtual memory. The driver then encapsulates all the compressed files into one large file on the disc. To the computer, it looks like one large ISO 9660 file. The CRI-X2 Driver, however, sees all the files as compressed DOS FAT files.

CapaCD, EWB's compression utility, takes a similar approach in that it encapsulates the compressed files into one large file. But the program sees the data in the file in either ISO 9660 or Apple HFS format. The advantage to this approach, according to EWB, is that it avoids the limitations of the DOS file system, including its 2-GB maximum vol ume size.

EWB says its own ``distributed indexing'' scheme, where each compressed file carries its own indexing data, offers another advantage: It provides faster file access. The CRI-X2 Driver places all the indexing data in one header for the entire compressed volume. EWB says that the CapaCD utility will be available sometime during the third quarter.

While CD-ROM USA uses the popular Stac compression engine, EWB has gone with its own engine, which is called Multipress. Actually, it is several engines; each, the company claims, is optimized for a particular data type, such as text, image, or audio.

EWB president Ed Brakus sees the choice between the two engines as a technology issue. ``Stac will need to develop an entirely new compression technology to catch up,'' he says. CD-ROM USA is banking on Stacker's proven track record and the close ties between Stac Electronics and Microsoft (Stac and Microsoft announced in June a cross-license agreement to end their disk-compression patent di spute).

In reality, there is likely room for both engines. Some companies need as much compression as they can get. Others will sacrifice the smallest possible file size for a familiar and trusted compression method.