DOS

1) Various forks of Gary Kildall's cp/m. These usually use monolithic singletasking, although programs running under DOS can be written to exhibit multitasking. 2) Microsoft DOS, one of Microsoft's first example's of making money off of borrowed code. Microsoft bought QDOS (Quick and Dirty Operating System) from Tim Patterson in the early 80s. As a result of this, a chain reaction started and Microsoft products now run on approximately 90% of all computers despite their steep prices and reputation of crashing. MS-DOS uses the FAT12 and FAT16 systems natively, and are also fundamental parts of non-NT Windows implementations.