July 27, 2011 By Chad Vander Veen
Answer: MS-DOS
According to RegHardware.com, "On 27 July 1981, Microsoft gave the name MS-DOS to the disk operating system it acquired on that day from Seattle Computer Products (SCP), a hardware company owned and run by a fellow called Rod Brock."
Read the rest of the history of DOS in RegHardware's great article.
You may use or reference this story with attribution and a link to
http://www.govtech.com/newsletters/Question-of-the-Day-for-072811.html