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1.
Microsoft Disk Operating System.
Guy 1: MS-DOS is a great operating system.

Guy 2: Yeah, too bad few know how to use it.
by Anonymous August 11, 2003
 
2.
An operating system which is also the origin of the name of a notorious family. Acronym for MicroSoft Disk Operating System.
Fundo thought MS-DOS sounded cool, but two wasn't his favorite number, so he changed his last name to something else that was similar to that.
by authOOr August 08, 2006