On 01/15/2012 03:17 AM, Steve Nickolas wrote:
Basically, a few "common" sectors written on track 0 both in DOS 3.2 style
and in DOS 3.3 style, then 2.5 tracks containing the rest of the DOS
image, probably 3.2.1, reordered and with a different loader.
I think the way it was usually done was to have everything in 13-sector
format, except for one single boot sector that can be read by the
16-sector controller card. That sector then just contains an equivalent
of the 13-sector boot ROM and the first thing it does is to simply load
the 13-sector boot sector and jump to it. From there, everything is
almost the same for the two code paths; the 13-sector boot sector is
modified only insofar as it detects whether it has been read in directly
by a 13-sector controller card or by the 16-sector boot sector and
adjusts accordingly (boot sectors generally re-use some part of the
controller ROM routines since they're too small to do anything useful
without that trick).
At least that seems to be what the original release of "Ultima" (later
known as "Ultima I") does, the only universal booter I have looked at in
some detail.