What are the really unusual or weird computers?

Hi, Their own special version in as much as each CP/M system having it's "own version" of CP/M. MS-DOS was such a blatant copy of CP/M, that you could tailor it to your target hardware in much the same way you did with CP/M. You pretty much just needed to produce a custom "IO.SYS" for your hardware and you were away - in the early days at least. Correct, the BIOS was very much their of their own design. In terms of their architecture, about the only similarity between the IBM PC and the Apricot is that they use the i8088. Other than that.... I don't believe so; even if you could somehow coax the machine to boot without a BIOS, I believe MS-DOS requires its presence. Depends which version of MS-DOS, I believe that at some point (MS-DOS 4?) M$ made it IBM only. You'd also have to produce your own custom "IO.SYS", and I'm not sure if "MSDOS.SYS" isn't involved here too. TTFN - Pete.