Microsoft disk operating system

/M S doss/ (Or "MS-DOS", "PC-DOS", "MS-DOG", "mess-dos") Microsoft Corporation's clone of the CP/M disk operating system for the 8088 crufted together in 6 weeks by hacker Tim Paterson, who is said to have regretted it ever since. MS-DOS is a single user operating system that runs one program at a time and is limited to working with one megabyte of memory, 640 kilobytes of which is usable for the application program. Special add-on EMS memory boards allow EMS-compliant software to exceed the 1 MB limit. Also know as PC-DOS or simply DOS, ignoring the fact that there were many other OSes with that name, starting in the mid-1960s with IBM's first disk operating system for the IBM 360.

Free Online Dictionary of Computing