🚀 go-pugleaf

The answer, I believe, is that *all* Atari floppy drives think they are
drive 1.  This is why you don't have to muck with jumpers when you get an
Atari drive, regardless of whether you are using it as a second drive, or as
the first drive on an old system with no builtin floppy.  The drives are
'daisy-chained', and the select lines will be crossed over inside each
drive -- so that when the computer asserts 'Drive 1', the first drive responds.
When the computer asserts 'Drive 2', the passthru in the first chained drive
passes that to 'Drive 1 select' on its daisy-chained OUTPUT side, so that
drive B sees it as a 'Drive 1 select' signal.

So, if you are chaining your 5.25 inch drive in in the normal way (i.e.
plugged into the back of drive A if A is external, or plugged into the back
of the ST if drive A is internal, you've got to set the jumpers on the 5.25
inch drive so that it thinks it is drive 1.