Format
The disk format used GCR in a manner very similar to that of the Disk II. The drive contained circuitry to allow software control over the motor speed, which was used to maintain near constant flux transition rate on all tracks, so that more data could be stored on the outer tracks.
Each physical sector stored 512 data bytes and 20 tag bytes. The controller used similar circuitry to the Disk II controller, but ran at twice the clock rate. The controller used a dedicated MOS 6504 microprocessor; in the Lisa this was on the system I/O card, and for the UniFile/DuoFile products, it was on an interface card that plugged into a peripheral expansion slot. The Lisa 2/10 and Macintosh XL I/O card used the IWM controller chip to replace the TTL chips of the earlier design.
Read more about this topic: Apple File Ware