Integrated Woz Machine

The Integrated Woz Machine, or IWM for short, is a single-chip version of the diskette drive controller of the Apple II , which was also used in Macintosh computers.

When creating a floppy disk drive for the Apple II, Apple co-founder Steve Wozniak decided that the solutions available on the market were too complicated, too expensive and ineffective. Instead of using floppy drives with the Shugart interface common at the time , Wozniak only used the drive mechanics and developed his own electronics for both the drive and the computer-side controller.

In fact, he succeeded in creating a more powerful solution with significantly fewer components. Instead of the 8-10 sectors of 256 bytes per track that were common at the time , he managed to implement 13 sectors of 256 bytes each with the same mechanics and the same media. In a later version it even achieved 16 sectors per track.

Initially, the drive controller was made up of several logic modules and a PROM . With increasing numbers at Apple, a version combined in a chip was later developed, this was the IWM. The IWM was u. a. Used in Apple IIgs and all Mac models up to Macintosh II. The IWM was then expanded to include the option of reading and writing floppy disks in FM and MFM format (also known as DOS format). The name of the new chip was "SWIM". In later Mac models, the SWIM was then integrated into larger peripheral components until Apple finally banned the floppy disk drives from the Mac. The function remained in the chipsets for some time, even if there was no longer a drive on the Mac, e.g. For example, the first iMacs even had a plug for a floppy drive on the mainboard , which hobbyists also partially retrofitted.