BASIC rom compatibility

Like you, I use the word 'clone'to mean a machine with the same hardware interface and same ROM BIOS calls as the IBM machine it claims to be a lcone of, and thus it runs the same OS (yuo can boot said machine from a disk that will boot the IBM machine) and which runs the same software. Of coruse soem early clones _did_ have incompatibilities. I tend to use the term 'IBM incompatible' for an 80x86-based personal computer that is not compatible with the similar IBM machine. Things like the Rainbow, HP150, Apricot, etc. There are several levels of incompatibility -- the hardware may be differnt (so that programs that 'hit the mrtal' won;t run, the BIOS calls may be different (so that programs thtat use said calls won't run), etc. Of coruse ther are plenty of other machines that are not compatible with any IBM, but I don;'t tend to refer to thsoe as 'IBM incompatibles'. I've also been known to use the term 'IBM compatible' in a jocular way, for example when I said I'd jsut been given an 'IBM compatible ethernet interface'. This happened to be a Storagetek unit to link to an IBM 370 channel. As for the original question, IIRC if the IBM bios fails to find a boot device, it calls a particular software interrupt, which is set to the cold start point of the BASIC ROM. Whether this ROM would work on not-100%-compatibles depends on just what that ROM does about directly accessign hardwre. -tony