shattered, than you for reply, though it's confusing, because there is a difference in behaviour depending on this switch position.

I have a bunch of plain floppy images:

copies of real floppies,
or downloaded from internet,
or prepared by dd count=$((9*2*$ntracks)) and then formatted from within emulator or mapped and formatted as loop device in linux etc etc.

All these images work fine when they are 360 KB _and_ mentioned switch is set to "40 tracks".

None of these images (of any size) are recognized when your switch is set to "80 tracks".
I've tried to set media descriptor byte (at 0x15 offset) to F9 (most 720k images already has it), without success.

All I want is to emulate authentic DS/DD floppies, which were most commonly used on 1841 and usually formatted to 80/2/9 CHS (720 KB).
Is this possible, did you try this?

You can answer me in Russian in private, if you wish.