The Surprising Truth Behind IBM PC-DOS


IBM PC-DOS 1.1 User manual and diskette

By Jack Rice
April 29, 2020

Did you ever wonder who came up with the operating system on your computer or smartphone? Believe it or not, it’s origins stem from the early beginnings of companies like Microsoft and Apple but also had a huge impact from little companies that no longer exist.

DOS stands for Disk Operating System. Most of the emerging computers at the time, especially personal computers (where the acronym PC originated), used 5¼" floppy disc drive. These new personal computers needed an OS in order to tell the hardware how to interact, just like Windows, Mac-OS, etc. do today. The difference was, they couldn’t permanently load these operating systems onto the computer itself, so they used floppy discs.

IBM needed an OS to ship with their latest creation, the IBM PC 5150. At first, they went to Bill Gates who had created Microsoft thinking he had an OS, but Gates had only been working on a programming language, BASIC.1 Gates told them to go to Digital Research who had an OS but refused to let IBM buy it from them and change the name, Digital Research wanted royalties on every copy sold.2 So, they went back to Microsoft, and Gates contacted Tim Patterson from Seattle Computer Products who came up with a rough copy of DOS that was based on CP/M (Digital Research’s operating system). After this, Microsoft bought it and worked out a deal with IBM where they would continue to develop their own versions of DOS independently.3

Several years later, DOS mostly evolved into Windows, and Apple’s DOS evolved into their respective OS. The next time you are using your computer or phone, remember Tim Patterson and the little companies, which, while they are not around anymore, played a huge role.

  1. James Wallace and Jim Erickson, Hard Drive: Bill Gates and the Making of the Microsoft Empire (New York: Wiley, 1992), 15-16, 85-88. 

  2. Paul Freiberger and Michael Swaine, Fire in the Valley: The Making of the Personal Computer, Second Edition (New York: Mcgraw-Hill, 2000), 332–33,

  3. See "The Television Program Transcripts: Part II," PBS Companion Website - Triumph of the Nerds Starring Robert Cringely,; and Microsoft and Seattle Computer Products, "Agreement of Sale", July 27, 1981, 1-7,