Another disk imaging project

[Scott Stevens]

On Fri, 5 Aug 2005 23:49:45 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:

> > 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.
> 

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.