As its name probably suggests, it is an Exec device, similar in the way of
operating to Matt Dillon's fmsdisk.device. Like that, in fact, it allows
you to create virtual disks, whose tracks are saved on a file. Unlike that,
however, it uses a different file for each track, and compresses the
tracks. This allows you to create virtual partitions on your hard-disk,
usable like normal partitions, but having the great advantage that every
file you write is automatically compressed (and obviously, it is decompressed
whenever you read it back).