A disk compression utility overrides the standard operating system routines.
A good disk compression utility could, on average, double the available space with negligible speed loss.
Disk compression fell into disuse by the late 1990s, as advances in hard drive technology and manufacturing led to increased capacities and lower prices.
Some of the initial disk compression solutions were hardware-assisted and utilized add-on compressor/decompressor coprocessor cards in addition to a software driver.
Bundled utilities included (in chronological order): While Windows XP, from Microsoft, included both a native support and a command named compact that compresses files on NTFS systems, that is not implemented as a separate "compressed drive" like those above.
Disk compression usually creates a single large file, which becomes a virtual hard drive.