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 drives:
https://voidstar.blog/5150-setting-up-floppy-disk-controller/ 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: https://voidstar.blog/ibm-pc-5150-notes/ On Sun, Feb 26, 2023 at 5:55 PM Fred Cisin via cctalk <cctalk@classiccmp.org> wrote: > > Which versions of DOS let you boot off B: ? > > CORRECTION: > 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 changing > 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: will > 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 is > 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 ci...@xenosoft.com >
