Comment by ralferoo

Lots of people are commenting on how unique it was to have a software based disk interface instead of stand alone hardware. And in a sense that is true, but also not.

Around that time there were various iterations of floppy controllers, each having a small microprocessor at their core. Just before the Apple Disk II, NEC released the uPD765 which is contains everything needed in one chip, but actually it's mostly just a small microprocessor taking a very similar approach under the hood in terms of track decoding. In fact the uPD in the part name is a giveaway that the implementation is a microprocessor instead of logic gates (and the command and reply interface). That operates a lot more like the Commodore drive, except it has a parallel interface with the host processor instead of a serial interface.

Sadly, I don't know anybody who's attempted to extract the ROM out of that microprocessor and reverse engineer it, but I'd definitely be fascinated to see that for faithful emulation purposes (at least for my emulator, I just implemented the interface as described in the datasheet).