> The IWM just reduced it to one chip allowing them to eliminate the controller PCB) From the Wikipedia article: "The floppy drive controller was built with 8

> The IWM just reduced it to one chip allowing them to eliminate the controller PCB) From the Wikipedia article: "The floppy drive controller was built with 8 ICs, one of which is the PROM, containing tables for the encoder and decoder, the state machine, and some code." (My emphasis.) What made it at all possible was moving most of the logic to the CPU: https://retrocomputing.stackexchange.com/a/7188 https://retrocomputing.stackexchange.com/a/7188 The IWM chip, used in the prototype Mac with double sided "Twiggy" drives, and later in the original production Mac 128k with Sony 3.5" diskette drives, is basically Woz's original disk controller design (converted by Wendell Sander and Bob Bailey to NMOS), with the addition of buffer registers to allow the processor to run a bit more asynchronously. But, except for not having to run (* almost) synchronous with the disk data rate, the 68k CPU did all the raw data decoding (GCR nibbles to bytes, etc.) and head stepping in software, very similar to the 6502 code in the Apple II (DOS) RWTS.