DriveSpace

DriveSpace (initially known as DoubleSpace) is a disk compression utility supplied with MS-DOS starting from version 6.0 in 1993 and ending in 2000 with the release of Windows Me.

Microsoft had originally sought to license the technology from Stac Electronics, which had a similar product called Stacker, but these negotiations had failed.

DoubleSpace also consumed a significant amount of conventional memory, making it difficult to run memory-intensive programs.

A company called Blossom Software claimed to have found a bug that could lead to data corruption.

The bug occurred when writing files to heavily fragmented disks and was demonstrated by a program called BUST.EXE.

This created the possibility of a kind of internal fragmentation issue, where DoubleSpace would be unable to find enough consecutive sectors for storing a compressed cluster even if plenty of space was available.

Microsoft attempted to remedy this in the MS-DOS 6.2 version of DoubleSpace (via a feature called DoubleGuard that would check for such corruption).

Other products, like later versions of Stacker from Stac Electronics, were capable of converting existing DoubleSpace compressed drives into their own format.

The program SCANDISK introduced in this release was able to scan the non-compressed and compressed drives, including checks of the internal DoubleSpace structures.

Security features (known as DoubleGuard) were added to prevent memory corruption from leading to data loss.

Following a successful lawsuit by Stac Electronics regarding demonstrated patent infringement, Microsoft released MS-DOS 6.21 without DoubleSpace.

MS-DOS 6.22 contained a reimplemented version of the disk compression software, but this time released under the name DriveSpace.

Windows 95 had full support of DoubleSpace/DriveSpace via a native 32-bit driver for accessing the compressed drives, along with a graphical version of the software tools.

This caused difficulty for users rebooting into the MS-DOS mode of Windows 95 for running games, because of the reduced amount of conventional memory that was available.

DMSDOS, a Linux kernel driver,[6][7] was developed in the late 1990s to support both the reading and writing of DoubleSpace/DriveSpace disks.