Digital Research wrote in the CP/M manual that

"The BIOS and BDOS are logically combined into a single module with a common entry point and referred to as the FDOS. "

What is FDOS an abbreviation for?

  • 5
    according to wikipedia: "FDOS may refer to: Floppy Disk Operating System, a term sometimes used to describe early floppy-based disk operating systems such as CP/M"
    – Tommylee2k
    Commented Jan 16, 2023 at 16:21
  • @Tommylee2k, I don't think it's that. From the CP/M documentation, FDOS refers to the combined BIOS and BDOS, as the question says. That Wikipedia definition sounds more like a backronym to me.
    – TonyM
    Commented Jan 16, 2023 at 23:03

1 Answer 1


I recall seeing it expanded to Full Disk Operating System (since a BIOS+BDOS together are sufficient to run CP/M programs).

  • Was that a backronym?
    – RonJohn
    Commented Jan 18, 2023 at 1:58
  • 1
    @john_e I assumed "full disk operative system" before I asked here. But since I know CP/M changed meaning from "monitor" to "microprocessor" (and I like to understand things evolutionarily) I asked anyway. I think it's possible Kildall changed the meaining of the term "FDOS" too. That it might have started to mean "Full Disk Operative System" or possibly "Flexible Disk Operative System" after he added BIOS component (and lumped the BDOS with it), but that the term was also around before that and meant "Floppy Disk Operative System".
    – BipedalJoe
    Commented Jan 19, 2023 at 7:26
  • 1
    The term "Floppy Disk Operative System" was mentioned in 1976, referring to CP/M, Warren, Jim (April 1976). "First word on a floppy-disk operating system". Dr. Dobb's Journal. And, IMSAI used the term too, bitsavers.org/pdf/imsai/dos-a/…, and I think they were first to popularize CP/M. And, "FDOS" appears in 1975 source code from Kildall, cpm.z80.de/source.html.
    – BipedalJoe
    Commented Jan 19, 2023 at 7:28
  • @BipedalJoe You might as well write up those comments into an answer. Commented Jan 20, 2023 at 19:12
  • user3840170 The first half sure, the two references to "Floppy Disk Operating System". But I'm more interested in what john_e wrote, because that is what I assumed myself, and I have little on that, only thing I could add is the wild guess that Gary could have changed the meaning of FDOS like he did with CP/M.
    – BipedalJoe
    Commented Jan 21, 2023 at 7:26

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