Put a B sticker on the drive that boots, done.
For a PC and any Tandon drive system there is a mechanical constraint to
what drive is the boot drive. Jumpers and cable turn a generic tandon
100-x into the boot drive. It's not a ROM thing. The Osborne I *does*
have a built-in ROM key-triggered A/B switch, DEC Robin too, Various
others but not the PC BIOS.
You could make the disk in drive A bootable, put a minimum OS on it, add a
line ATTRIB B:; and PATH B; to an autorxec.bat that allows the computer
to.pull most DOS files off the B drive, so you can have max space on the A
drive for another program. There are books .from the period full of DOS
tricks, but the OS level is not the hardware level. Blah blah
On Wed, Mar 1, 2023, 3:26 AM Steve Lewis via cctalk <cctalk(a)classiccmp.org>
Can't help with booting DOS to a B: drive. But,
in case of interest - I do
keep the IBM PC 5150 notes here:
Specifically as might be related here, I have some notes on using 4 disk
And main point is, the DOS DRIVER.SYS might let you control the disk drive
letters in a way that
might help in some way. I think it was available pretty early on -- if not
PC-DOS 1.0, at least PC-DOS 2.0.
DEVICE=\DOS\DRIVER.SYS /d:2 /t:80 /s:9
DEVICE=\DOS\DRIVER.SYS /d:3 /t:80 /s:9
There is also a SUBST command. Can't remember if SUBST lets you override
an existing letter -- I think is probably does.
But if you don't have a B: drive at all, you can do something like:
SUBST B: C:\UTILS
Then the whole B: drive gets substitutes to that given folder.
My more main IBM PC 5150 notes are here:
On Sun, Feb 26, 2023 at 5:55 PM Fred Cisin via cctalk <
versions of DOS let you boot off B: ?
Although the default of DOS used to be A: then first HDD (usually C:), it
is the computer firmware, not DOS that decides that.
The assumption that C: is the HDD can be annoying. I used to use PCs with
four floppies. If jumpered properly, the HDD was E:.
Many "modern" PCs, within the "CMOS" setup, have provision for
the boot sequence. Mostly, in order to default to booting from HDD,
rather than floppy, but also for CD or USB boot.
I do not know of any that permit selecting floppy B: for boot, but there
could exist some with that option, . . .
On a PC with a single physical floppy, asking for any command with B:
trigger a prompt to put the B: disk in drive A:,
and have a phantom B:
that shares the physical drive with A:
Swapping A: and B: is, of course, trivial to do with hardware, and/or
messing with the cable. (pin 10 of the cable [at the FDC] is A: and 12
B:, but the usual supplied cables are twisted and
missing pins so that
every drive, on the drive itself is jumpered as if it were B:). An
untwisted cable, with switch[es] would be one way.
Grumpy Ol' Fred cisin(a)xenosoft.com