Most of the games will only run from #8. Even if you added a 8/9-Switch to your
internal C128 drive, some games and demos do not like if there is a 2nd drive on
the bus.

So, the good news:
With S.T.F.U. you can disable your internal drive by software:
https://csdb.dk/release/?id=160842

1. Set your 1541-U drive emulation to #9 or OFF
2. Start and run the file. (In my case I had to load it from disk - it does not
seem to work if you DMA-start it from your 1541-U).
3. Select and deactivate your internal 1571.
4. Set your 1541-U to #8 and use it as regular drive.

This did work on my C128D. It did not work on my SX64.
However it might be of interest for C128D users.

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