Trully C128D is a 2 apart units embedded in one case (C128 and 1571) so you can't recognize connected external 1571 to c128D also. You could be try compare kernal ROM and DOS ROM for guessing. I never had any C128.
I'm guessing the subject is about the serial burst mode between commodore and 1571 with used additional SQR line. Also the BURST people called a hardware mod using additional 8 free lines from unused port of VIA and connected this to USER PORT in commodore. Also here was done hardware handshaking. Years ago I had this mod. Seriously this never did not convince me bcos often had a some write errors. So I leave this.
That's my old tool for use additional space on the disk on the illegal track's 36/41-42
We can talk about programming drives. I tried still compatibile between 1571/70/1541C/1541 II (1570/71 in single mode (GCR) without MFM of course). Some times like here www.youtube.com/watch?v=Q76ZepI_44Y you can do realtime 3d vertex calculated in drive. Sadly here is 2KB of RAM only.
About tape is really little to say. Only ABC turbo. Sometimes people done IRQ tape loaders, but allways tape was very very slow. Even in ABC turbo
That web page spends a few paragraphs to say why a C64 was never done... basically it was "too hard for the C64"... until these guys came along (who still haven't released anything... or so it seems... correct me if I'm wrong). Umm, can you say VAPORWARE? Good... I knew you could!
offtop Yeah - Commocore was delayed. Thats way I did and releassed CBM Asteroid by self. Build from scratch. Work on the c64/128/PAL/NTSC
Retrokomp/Load error 2013 party 2nd place for game competiton