🚀 go-pugleaf

I just bought a floppy head cleaner kit (after a bad experience with some
crappy disks), and have been trying to write a program to exercise the
heads while the cleaning disk is in place.  DOS and the BIOS don't seem to
like the idea of it at all, so I'm programming the floppy disk controller
directly, according to instructions from Robert Jourdain's book.

Things are going well when I give my program a valid drive number to work
on.  My problem is that I can't determine whether the drive number is valid.
The DOS/BIOS services try to read the disk, so that's no good; the equipment
list always tells me I have 2 floppy drives, when in fact I have one; the
"Sense Drive Status" command described in Jourdain doesn't seem to give any 
different answer whether I ask about the drive that's there or the one that's
not.  I suspect a misprint, because there are lots of others in this section
of the book.  On an AT, I think I could query the CMOS RAM, but that doesn't
help here.

Can anyone tell me how to make this simple determination?  And after that,
is it safe to assume that any XT clone will be using 40 track disks? 

Duncan Murdoch