5 Aug
2005
5 Aug
'05
7:49 p.m.
On Fri, 5 Aug 2005 23:49:45 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
That's interesting, because I thought that BIOS extension ROMs were part
of the 'PC Standard' from the beginning. I'm not disputing you at all,
btw.
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.