Compressed volumes only work with a compression driver, which must be loaded before the
compressed disk can be used. This is only an issue for compressed volumes running under
DOS or Windows 95. The problem is that this driver can be rather large, and can exacerbate
conventional memory problems.
Normally, DriveSpace 2 (or DoubleSpace) is used for older DOS versions, and DriveSpace
3 for Windows 95. Under DOS, the DriveSpace 2 driver can be loaded into an upper memory block to reduce conventional memory usage,
and this driver is not excessively large. Under Windows 95, the DriveSpace 3 driver is
large, but the system provides protected mode
compression drivers that run in extended memory, so there isn't a problem with
conventional memory being used by the driver.
The real problem occurs when Windows 95 drops down to MS-DOS mode; here the real-mode
DriveSpace driver must be loaded to conventional memory, and it is quite large. This
problem is a valid one and cannot be eliminated. Good conventional memory management can
reduce the problem, but cannot remove it completely.
Next: Compatibility and Reliability Issues in Volume
Compression
