Slack is the space wasted due to unused storage at the end
of large clusters. When a great number of files are stored on a disk with a large cluster
size, a lot of the disk is wasted due to overhead. One way to eliminate this is to use a
utility program to create a ZIP file archive, for example, containing all the files. But
this results in the files not being readily accessible.
Volume compression tools like DriveSpace 3 can in fact save space even when set not to
compress any files at all, due to slack space reduction. Internally, DriveSpace 3
compressed drives allocate files on a sector-by-sector basis. This means that they have an
effective cluster size of 512 bytes, because they use an internal format that lets
them store more than one file in what would be a cluster on a regular drive.
Some people set up DriveSpace 3 volumes just to get this advantage. It can be
configured so that no files are actually compressed (for performance reasons, to save on
the overhead of decompression) but you still get the slack reduction because of the slack
reduction feature. You still have some of the risks associated with using a compressed
volume however, and also the loss of some memory for the compressed volume driver, which
has to operate even if you set it to no compression (slack reduction only).
Next: Compression Level and Performance Considerations
