the full version of DriveSpace 3. DR-DOS 7.03 (1999), from Caldera, included a DPMS-enabled version of Stacker 3.12. Windows 98 SE (1999), from Microsoft, included the full version of DriveSpace 3. PTS-DOS Pro 2000 (1999), from Paragon Technology Software, included a disk compression component named DATACOMP. Other solutions Squeeze, a resident DOS file compressor for Lotus 1-2-3 and Lotus Symphony files from Turner Hall Publishing Squish Plus ROM from Sundog Software, but distributed exclusively through Personalized Software (now Thaddeus Computing), was a special ROM chip containing a custom version of Squish Plus with only 36 KB footprint adapted for the HP Portable Plus. Double Tools for DoubleSpace from Addstor was an add-on product, enhancing the functionality of the DoubleSpace bundled with MS-DOS 6.0. Multimedia Stacker from Helix Software was a bundle of Stac's DPMS-enabled Stacker 4.01 combined with Helix Cloaking and utilities, utilizing Cloaking's built-in DPMS server to relocate and run in protected mode. THS filesystem (1994–1996 by Thomas Scheuermann), a compressed file system driver for Linux, which could read some CVFs. DMSDOS (1996), a Linux kernel driver, to support the reading and writing of DoubleSpace, DriveSpace 2 & 3, as well as Stacker 3 & 4 volumes. While Windows XP, from Microsoft, included both a native support and a command named that compresses files on NTFS systems, that is not implemented as a separate "compressed drive" like those above. Operation Disk compression usually creates a single large file, which becomes a virtual hard drive. This is similar to how a single physical hard drive can be partitioned into multiple virtual drives. The compressed drive is accessed via a device driver. Compressing existing drives All drives would initially be empty. The utility to create a drive would usually offer to "compress a current drive". This meant the utility would: Create an empty compressed drive, stored on the existing drive. Transfer existing files on the old drive to the new compressed drive. Increase the size of the new compressed drive as necessary to accommodate more files and allow empty space when done. When all files were transferred, the drive letters would be swapped. Usually certain system files would not be transferred. For example, OS swap files would remain only on the host drive. Compressing the boot drive A device driver had to be loaded to access the compressed drive. A compressed drive C: required changes to the boot process as follows: