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{{Short description|Single-chip version of the floppy disk controller for the Apple II}}
{{refimprove|date=December 2015}}
{{Use dmy dates|date=August 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
[[File:Interface Card - Disk II Interface Apple2.jpg|thumb|Original disk II controller. ''Integrated Woz Machine'' implemented all their logic on a single chip.]]
The '''Integrated Woz Machine''' (or '''IWM''' for short) is a single-chip version of the [[floppy disk controller]] for the [[Apple II]]. 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.<ref name="Williams_1985_Byte"/><ref name="Schematics">{{cite web
|url=https://embeddedmicro.weebly.com/apple--disk-drive-schematics.html |title=Apple II/II+ Disk Drive interface schematics |access-date= July 22, 2022}}</ref>

Wozniak successfully came up with a working floppy drive with a greatly reduced number of electronic components. Instead of storing 8–10 [[disk sector|sector]]s (each holding 256 [[byte]]s of data) per [[track (disk drive)|track]] on a [[Floppy disk#5.C2.BC-inch floppy disk|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]].<ref name="Williams_1985_Byte"/>

The floppy drive controller board, the "Disk II interface,"<ref name="Schematics" /> was built with 8 [[Integrated circuit|chips]], one of which is the [[Programmable read-only memory|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.<ref name="5Macs"/>

The IWM is essentially a disk controller on one IC. It was employed in the [[Apple IIc]], and later [[Apple IIGS]], 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 [[Digital frequency modulation|FM]]- and [[Modified Frequency Modulation|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]]s still had a floppy drive connector on its [[motherboard]], allowing a floppy drive to be retrofitted by knowledgeable enthusiasts.<ref name="iMac"/>{{Sps|date=July 2019}}

==See also==
* [[Paula (Commodore Amiga)]]

==References==
{{Reflist|refs=
<ref name="Williams_1985_Byte">{{cite journal |title=The Apple Story / Part 2: More History and the Apple III |journal=[[BYTE]] |publisher=[[UBM Technology Group]] |volume=10 |number=1 |issn=0360-5280 |oclc=637876171 |date=January 1985 |author-last1=Williams |author-first1=Gregg |author-last2=Moore |author-first2=Rob |type=interview |page=167 |url=http://apple2history.org/museum/articles/byte8501/ |access-date=2013-10-26 |url-status=dead |archive-url=https://web.archive.org/web/20120212185115/http://apple2history.org/museum/articles/byte8501/ |archive-date=2012-02-12}} [https://archive.org/stream/byte-magazine-1985-01/1985_01_BYTE_10-01_Through_the_Hourglass#page/n167] (NB. Interview with Steve Wozniak, where he describes creating the Apple version of GCR.)</ref>
<ref name="5Macs">{{Cite web |title=Five Different Macintoshes |website=www.folklore.org |url=https://www.folklore.org/StoryView.py?story=Five_Different_Macs.txt}}</ref>
<ref name="iMac">{{Cite web |title=iMac Floppy Kit |website=imac-floppy.com |publisher=Corporate Systems Center |date=2001-04-14 |url=http://imac-floppy.com:80/index.html |url-status=dead |archive-url=https://web.archive.org/web/20010414043026/http://imac-floppy.com/index.html |archive-date=14 April 2001 |access-date=24 January 2020 }}</ref>
}}

==Further reading==
* {{cite book |title=Integrated Woz Machine (IWM) Specification |author=Apple Computer, Inc. |author-link=Apple Computer, Inc. |date=February 1982 |orig-year=1978 |edition=19 |publisher=DigiBarn Computer Museum |url=http://www.brutaldeluxe.fr/documentation/iwm/apple2_IWM_Spec_Rev19_1982.pdf |access-date=2016-08-06 |url-status=live |archive-url=https://web.archive.org/web/20160806095036/http://www.brutaldeluxe.fr/documentation/iwm/apple2_IWM_Spec_Rev19_1982.pdf |archive-date=2016-08-06}}
* [https://ieeemilestones.ethw.org/Milestone-Proposal:Introduction_of_the_Apple_Macintosh_Computer,_1984 ]

{{Apple hardware before 1998}}

[[Category:Apple Inc. hardware]]

Integrated Woz Machine - Revision history

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