DoubleSpace was the original name of the disk compression software that was supplied with MS-DOS starting from version 6.0. The purpose of DoubleSpace was to increase the amount of data the user could store on disks, by transparently compressing/decompressing data on-the-fly. It was primarily intended for use with harddrives, but use for floppy disks was also supported. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...

How it worked

In the most common usage scenario the user would have one hard drive in the computer, with all the space allocated to one partition, which would then have the drive letter C. When the user ran DoubleSpace for the first time, it would offer to compress this drive. The compression was a lengthy process which could take hours to complete. After the process, all the files previously on the drive would have been compressed and would be stored in one big file, usually called DBLSPACE.000. The compression process would also enable a special DoubleSpace driver to be loaded as part of MS-DOS during boot. Upon loading this driver would change the drive letter of the actual drive on the disk to H (which was also known as the Host Drive) and would then map the drive letter C to the compressed drive 'contained' in DBLSPACE.000, compressing and decompressing data as needed.

DoubleSpace could be used in other ways, however. Instead of converting an existing drive, one could create a blank compressed drive by using space on one of the actual drives in the system.

Initial public perception

Initially, DoubleSpace was surrounded by an air of mystery. Many had difficulties understanding how it was possible to store more data on the disk than it could actually contain. This led to much speculation, with some users thinking DoubleSpace changed the way data was stored physically on the disk, and there were rumours that using DoubleSpace would reduce the longevity of the disks or the computer itself. This was of course a misunderstanding; DoubleSpace used purely logical/software means to obtain its results and was not different from other compression tools like PKZIP except that it handled the compression/decompression transparently to the user. PKZIP is an archiving tool originally written by the late Phil Katz, and marketed by his company PKWARE, Inc. ...

DoubleSpace in DOS 6.2

DOS 6.2 featured a new and improved version of DoubleSpace. The ability to remove DoubleSpace was added. The program ScanDisk was introduced in this program was able to scan the compressed (including checks of the internal DoubleSpace structures) as well as non-compressed drives. Security features (known as DoubleGuard) were added to prevent memory corruption from leading to data loss. The memory footprint of the DoubleSpace driver was reduced compared to the version shipped in MS-DOS 6.0

MS-DOS 6.21

Following a lawsuit by Stac Electronics regarding alleged patent infringment, Microsoft released MS-DOS 6.21 which didn't contain DoubleSpace. Stac Electronics was an engineering company founded in 1984 by four friends at Caltech. ...

M-DOS 6.22

MS-DOS 6.22 contained a reimplemented version of the disk compression software, but this time released under the name DriveSpace. The software was essentially identical to the MS-DOS 6.2 version of DoubleSpace from a user point-of-view and was compatible with previous versions.

DriveSpace in Windows 95

Windows 95 had full support of DoubleSpace/DriveSpace featuring a native 32-bit driver for accessing the compressed drives along with a graphical version of the software tools. MS-DOS DriveSpace users could upgrade to Windows 95 without any troubles. Furthermore, The Microsoft Plus! for Windows 95 pack contained the program DriveSpace 3. This version introduced new compression formats (HiPack and UltraPack) with different performance characteristics for even greater compression ratios along with a tool that could recompress the files on the disk using the different formats, depending on how frequently the files were used etc. One could upgrade from the classical DriveSpace to DriveSpace 3 but not vice versa. One could however decompress a DriveSpace 3 drive. The DOS device driver of DriveSpace 3 had a memory footprint of around 150K causing difficulty for users rebooting into the DOS-mode of Windows 95 for running games, because of the reduced amount of conventional memory available. Windows 95 (codename Chicago) is a hybrid 16-bit/32-bit graphical user interface-based operating system released on August 24, 1995 by the Microsoft Corporation. ... Microsoft Plus! is an operating system enhancement package provided by Microsoft Corporation. ...

DriveSpace in Windows 98

Windows 98 shipped with DriveSpace 3 (unlike Windows 95 where this had to be obtained from the Plus! pack). Windows 98 (codename Memphis) is a graphical operating system released on June 25, 1998 by Microsoft. ...

Windows 2000/XP

Neither Windows 2000 nor XP supports DoubleSpace/DriveSpace and they can not access or be installed on drives compresssed using these tools. The NTFS file system has its own compression functionality, however. Windows 2000 (Codenamed Cairo, also referred to as Win2K, W2K or Windows NT 5. ... Windows XP is a major revision of the Microsoft Windows operating system created for use on desktop and business computer systems. ...