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 Apple II ("apple Roman numerals, two", stylized as Apple ][) is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The Apple II (original), original Apple II model, which gave the series its name, was designed ...

. 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 un ...

s of data) per track on a 5.25-inch floppy disk — 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 chips, one of which is the PROM, containing tables for the encoder and decoder, the state machine, and some code.

Application and updates

To make it easier to place the controller on the main board, Wendell Sander integrated all these components into one single chip—the IWM. The IWM is essentially a disk controller on one IC. It was employed in the

Apple IIc The Apple IIc is a personal computer introduced by Apple Inc. shortly after the launch of the Macintosh 128K, original Macintosh in 1984. It is essentially a compact and portable version of the Apple IIe. The IIc has a built-in floppy disk driv ...

, and later

Apple IIGS The Apple IIGS (styled as II) is a 16-bit personal computer produced by Apple Inc., Apple Computer beginning in September 1986. It is the fifth and most powerful model of the Apple II family. The "GS" in the name stands for "Graphics and Sound" ...

, the Apple Lisa 2/10, 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 stayed in the chipset for a while thereafter, even though the provision of floppy drives for Macs had already ceased. For instance, the first

iMac The iMac is a series of all-in-one computers from Apple Inc., sold as part of the company's Mac (computer), Mac family of computers. First introduced in 1998, it has remained a primary part of Apple's consumer desktop offerings since and evol ...

s still had a floppy drive connector on its

motherboard A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see #Nomenclature, "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It ho ...

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

History

Application and updates

See also

References

Further reading