Memory Issues with Compression Drivers

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