This is a free download containing the four less common or long forgotton DOS versions: DOS 1, DOS 3, DOS 4, and DOS XE. DOS 2.5 (UK version master disk) is also in the ZIP file for completeness. These are all likely to be kicking around on the internet, but here all in one place if you want them. DOS 1 has no DUP.SYS, having the whole thing load into memory in one go, which is why DOS 2 quickly came along to replace it. DOS 3 is a total black sheep and hated by everyone. DOS 4 is a weird one, as it was, I believe, commissioned by Atari but scrapped and the rights returned to the programmer. DOS XE was designed to make the XF551 work in double sided mode, but was very late to market (1988) so it was hardly used by anyone.

The ZIP file contains the DOS boot disks in ATR format for use with emulators, or you can use them with SIO2PC/APE/ProSystem with a real Atari.