5 Aug
2005
5 Aug
'05
3:49 p.m.
I understand that the jump from the PC/1981 to
XT/1983
made it possible to boot from a HD, otherwise a floppy
had to be involved.
I am pretty sure some later PC BIOSes (not XT ones, specifically) allowed
booting from a hard disk.
More exactly, what was added was the search for extension ROMs. No IBM PC
or XT motherboard BIOS knew anything about hard disks. But the later ones
searched for extension ROMs before booting, and if any were found, a
routine in each extension ROM was executed. This routine could re-direct
software interrupt vectors to point to routines in the ROM, in
particular, the bootstrap vector could point to a routine in an extension
ROM that would attempt to boot from a hard disk before falling back to
the standard floopy drive boot routine.
-tony