Interface Card - Disk II Interface Apple2

The Integrated Woz Machine (or IWM for short) is a single-chip version of the floppy disk controller for the

Apple II The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-mold ...

. It was also employed in Macintosh computers.

History

When developing a floppy drive for the Apple II, Apple Inc. co-founder Steve Wozniak felt that the existing models available on the market were too complicated, expensive and inefficient. Rather than use the existing floppy drives from Shugart Associates, Wozniak decided to use the drive mechanism – but develop his own electronics separately for the both drive and the controller. Wozniak successfully came up with a working floppy drive with a greatly reduced number of electronic components. Instead of storing 8–10 sectors (each holding 256

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...

s of data) per track on a

5.25-inch floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...

— something standard at that time, Wozniak utilized group-coded recording (GCR), and with 5-and-3 encoding he managed to squeeze as many as 13 sectors on each track using the same mechanics and the same storage medium. In a later revision, this number was bumped up to 16 sectors per track with 6-and-2 encoding. The floppy drive controller board, the "Disk II interface," was built with 8 ICs, one of which is the PROM, containing tables for the encoder and decoder, the state machine, and some code. To make it easier to move the controller onto the main board, as in the Apple IIc, Apple IIGS, and Macintosh,

Dr. Wendell Sander Doctor is an academic title that originates from the Latin word of the same spelling and meaning. The word is originally an agentive noun of the Latin verb 'to teach'. It has been used as an academic title in Europe since the 13th century, w ...

integrated all these components into one single chip—the IWM.

Application and updates

The IWM is essentially a disk controller on one IC. It was employed in the Apple IIc, and later Apple IIGS, and all Mac models up to the Macintosh II. Later, an extended version, known as SWIM (Sander-Wozniak Integrated Machine), was introduced. This new version added the capability of reading and writing FM- and MFM-formatted (PC-formatted) floppy disks. In later Mac models, more and more peripheral components were added to the SWIM, until Apple finally phased out floppy drives from the Macs. The floppy controller function still stayed in the chipset for a while, even though the provision of floppy drives for the Macs had already ceased. For instance, the first

iMac iMac is a family of all-in-one Mac desktop computers designed and built by Apple Inc. It has been the primary part of Apple's consumer desktop offerings since its debut in August 1998, and has evolved through seven distinct forms. In i ...

s still had a floppy drive connector on the

motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...

, allowing a floppy drive to be retrofitted by knowledgeable enthusiasts.

History

Application and updates

See also

References

Further reading