This should be everything you need to build Atari DOS 2.5 from the original sources. Archive contents: README.txt - this file you're reading build.txt - build instructions (the file you should read next) builddos.atr - DOS 2.0S plus SAVEDOS.XEX and its source dossrc_a.atr - OSS DOS 2.5 FMS sources in Mac/65 format dossrc_b.atr - OSS DOS 2.5 DUP sources in Mac/65 format mac65.cart - Mac/65 v1.01 cartridge ROM image The source disks are the ones posted by Nir Dary on www.atariage.com. I haven't modified them at all, but you'll have to modify them slightly to build them.