Hi,
regarding the boot loader solution for reserving drive B: (int 13h unit 1) that I suggested in
http://svardos.org/?p=forum&thread=1725345339#1725445708
I prepared an lDOS pre-boot loader program, based on the lDebug debugger with some parts stripped out. This allows to load the fdbplace (floppy disk B: placeholder) extension. Current files at
https://pushbx.org/ecm/test/20251202/
You install either loaderu.com (uncompressed) or loader.com (compressed using LZSA2) as a kernel. Either rename it to a name used by another loader (eg kernel.sys), or set the name to use one of them (eg FreeDOS sys C: /bootonly /k loader.com, or lDOS instsect C: /f=loader.com). Then place fdbplace.eld into the root directory of the same drive.
To avoid having to enter the relevant commands while booting, I provided a small example loader.sld "Script for lDebug" file. This is the content:
:bootstartup
move bottom
ext fdbplace.eld install
move top
boot protocol freedos /fdkernel.sys
if (rc == 0) then g
Obviously this expects there to be a FreeDOS-compatible kernel in the file fdkernel.sys, but you can alter the filename or load protocol for other choices.
This installs a 1 KiB resident extension beyond the top of the Low Memory Area, moving around the EBDA if one is present. This extension pretends that there is a drive B: installed, which will always read as containing a 360 KiB diskette but always report as timing out on attempting to access it. (If there is no drive A: either then this should install two units that pretend there exists a drive.)
When the DOS loads, it will detect 2 diskette drives being present, so ethflop can install for drive B: without the headaches about the phantom drive in the DOS/BIO UPB structures.