MS-DOS 1.25

Thanks for the awesome repository. I've been able to boot up DOS 1.25 in Virtualbox without any issues. I'm trying to add some more data to the OS, but I'm unable to manipulate the floppy images outside of DOS - How is the .IMG created?

What I'm specifically trying to do is merge in the files found in the MS archive here: and create a more complete/official floppy image.

I'm running OSX as my daily driver, but I have Linux and Windows machines at my disposal.

The disk image for 1.25 is a different bird than a normal floppy image and DOS 1.25 won't read images created using HDIUtil (which makes DMG/FLP images).



  • MS-DOS 1.x didn't have the Bios Parameter Block that was created for DOS 2.x and tells what type of disk it is. I haven't seen a disk imaging tool that permits modification of a DOS 1 style disk.

  • You can manually add a BSP and then WinImage will recognize them. Although to maintain authenticity it is best to copy between disks with an emulator. (DOS 1.00 requires deleted marks on all unused directory entries, WinImage may clobber that).

    For simplicity, here are blank DOS 2.0 formatted 160k and 320k disk images that will open in WinImage.

  • Thanks for the blank disks and the tip on WinImage.

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