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The Disk II Floppy Disk Subsystem, often rendered as Disk ] floppy_disk_drive.html" ;"title="'', is a -inch Floppy disk, floppy disk drive">'', is a -inch floppy disk drive designed by Apple_Computer,_Inc._It_went_on_sale_in_June_1978_at_a_retail_price_of_US$495_for_pre-order;_it_was_later_sold_for_$595_()_including_the_Disk_controller.html" ;"title="Apple_Inc..html" ;"title="Steve Wozniak at the recommendation of Mike Markkula, and manufactured by Apple Inc.">Apple Computer, Inc. It went on sale in June 1978 at a retail price of US$495 for pre-order; it was later sold for $595 () including the Disk controller">controller card (which can control up to two drives) and cable. The Disk II was designed specifically for use with the Apple II personal computer family to replace the slower Cassette tape#Data recording, cassette tape storage. These floppy drives cannot be used with any Macintosh without an Apple IIe Card as doing so will damage the drive or the controller. Apple produced at least six variants of the basic -inch Disk II concept over the course of the Apple II series' lifetime: The Disk II, the Disk III, the DuoDisk, the Disk IIc, the UniDisk 5.25" and the Apple 5.25 Drive. While all of these drives look different, and use four different connector types, they're all electronically extremely similar. They can all use the same low-level disk format, and are all interchangeable with the use of simple adapters, consisting of no more than two plugs and wires between them. Most DuoDisk drives, the Disk IIc, the UniDisk 5.25" and the AppleDisk 5.25" even use the same 19-pin
D-Sub The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, no ...
connector, so they are directly interchangeable. The only " drive Apple sold aside from the Disk II family was a 360k MFM unit made to allow Mac IIs and SEs to read PC floppy disks. This is not the case with Apple's -inch drives, which use several different disk formats and several different interfaces, electronically quite dissimilar even in models using the same connector; they are not generally interchangeable.


History


Disk II

Apple did not originally offer a disk drive for the Apple II, which used
data cassette Magnetic-tape data storage is a system for storing digital information on magnetic tape using digital recording. Tape was an important medium for primary data storage in early computers, typically using large open reels of 7-track, later 9-t ...
storage like other microcomputers of the time. Apple early investor and executive
Mike Markkula Armas Clifford "Mike" Markkula Jr. (; born February 11, 1942) is an American electrical engineer, businessman and investor. He was the original angel investor, first chairman, and second CEO for Apple Computer, Inc., providing critical early f ...
asked cofounder
Steve Wozniak Stephen Gary Wozniak (; born August 11, 1950), also known by his nickname "Woz", is an American electronics engineer, computer programmer, philanthropist, inventor, and technology entrepreneur. In 1976, with business partner Steve Jobs, he c ...
to design a drive system for the computer after finding that a checkbook-balancing program Markkula had written took too long to load from tape. Wozniak knew nothing about
disk controller {{unreferenced, date=May 2010 The disk controller is the controller circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive. It also provides an interface between the disk drive and the bus conne ...
s, but while at
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
he had designed a simple, five-chip circuit to operate a
Shugart Associates Shugart Associates (later Shugart Corporation) was a computer peripheral manufacturer that dominated the floppy disk drive market in the late 1970s and is famous for introducing the -inch "Minifloppy" floppy disk drive. In 1979 it was one of the f ...
drive. The Apple II's lack of a disk drive was "a glaring weakness" in what was otherwise intended to be a polished, professional product. Speaking later,
Osborne 1 The Osborne 1 is the first commercially successful portable computer, released on April 3, 1981 by Osborne Computer Corporation. It weighs , cost US$1,795, and runs the CP/M 2.2 operating system. It is powered from a wall socket, as it has no on- ...
designer
Lee Felsenstein Lee Felsenstein (born April 27, 1945) is an American computer engineer who played a central role in the development of the personal computer. He was one of the original members of the Homebrew Computer Club and the designer of the Osborne 1, the ...
stated, "The difference between cassette and disk systems was the difference between hobbyist devices and a computer. You couldn't have expected, say, VisiCalc, to run on a cassette system." Recognizing that the II needed a disk drive to be taken seriously, Apple set out to develop a disk drive and a
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
to run it. Wozniak spent the 1977 Christmas holidays adapting his controller design, which reduced the number of chips used by a factor of 10 compared to existing controllers. Still lacking a DOS, and with Wozniak inexperienced in operating system design, Steve Jobs approached Shepardson Microsystems with the project. On April 10, 1978 Apple signed a contract for $13,000 with Shepardson to develop the DOS. Shortly after the disk drive project began in late 1977, Steve Jobs made several trips to Shugart's offices announcing that he wanted a disk drive that would cost just $100. After Wozniak finished studying IBM disk controller designs, Jobs then demanded that Shugart sell them a stripped disk drive that had no controller board, index sensor, load solenoids, or track zero sensor. Although puzzled by this request, Shugart complied and provided Apple with 25 drive mechanisms that they could use as prototypes in developing a disk system for the Apple II. The prototypes received the designation of SA-390. Wozniak studied
North Star Computers North Star Computers Inc. (later styled as NorthStar) was an American computer company based in Berkeley, California existing between June 1976 (when according to popular rumor it was formed as "Kentucky Fried Computers") and 1989. Originally a mai ...
and others' more complex floppy controllers. He believed that his simpler design lacked their features, but realized that they were less sophisticated; for example, his could use
soft-sectored Floppy disk format and density refer to the logical and physical layout of data stored on a floppy disk. Since their introduction, there have been many popular and rare floppy disk types, densities, and formats used in computing, leading to much ...
disks. Following the Shugart controller's manual, Wozniak attempted to develop an FM-type controller with 10 sector per track storage, but realized that Group Coded Recording could fit 13 sectors per track. Wozniak called the resultant Disk II system "my most incredible experience at Apple and the finest job I did", and credited it and
VisiCalc VisiCalc (for "visible calculator") is the first spreadsheet computer program for personal computers, originally released for Apple II by VisiCorp on 17 October 1979. It is often considered the application that turned the microcomputer from a hob ...
with the Apple II's success. Fellow engineer Cliff Huston came up with several procedures for resuscitating the faulty drives on the assembly line. When Apple sent an order into Shugart for more SA-390s, a Shugart engineer admitted that the disk drive manufacturer had been scamming Apple and that the SA-390s were actually rejected SA-400s that had failed to pass factory inspection. The idea was that Apple couldn't get the drives to work and would be forced to go back and purchase more expensive SA-400s. The Disk II was very successful for Apple, being the cheapest floppy disk system ever sold up to that point and immensely profitable for the company, in addition to having nearly 20% more storage space than standard FM drives. For a while, the only direct competitor in the microcomputer industry was the
TRS-80 Model I The TRS-80 Micro Computer System (TRS-80, later renamed the Model I to distinguish it from successors) is a desktop microcomputer launched in 1977 and sold by Tandy Corporation through their Radio Shack stores. The name is an abbreviation of ''T ...
, which had used only standard FM storage for 85k. Both the Atari 8-bit and
Commodore 64 The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness ...
's disk drives' throughputs were much slower than the Disk II's 15 KB/s, seriously affecting their ability to compete in the business market. However, the advantage of Wozniak's design was somewhat nullified when the cost of double-density MFM controllers dropped only a year after the Disk II's introduction. The initial Disk II drives (A2M0003) were modifications of the Shugart SA-400, which was the first commercially available -inch diskette drive. Apple purchased only the bare drive mechanisms without the standard SA-400 controller board, replaced it with Wozniak's board design, and then stamped the Apple rainbow logo onto the faceplate. Early production at Apple was handled by two people, and they assembled 30 drives a day. By 1982, Apple switched to
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drives for cost reasons. Normal storage capacity per disk side was 113.75 KB with Apple DOS 3.2.1 and earlier (256 bytes per sector, 13 sectors per track, 35 tracks per side), or 140 KB with DOS 3.3 and ProDOS (256 bytes per sector, 16 sectors per track, 35 tracks per side). The 16-sector hardware upgrade introduced in 1980 for use with DOS 3.3 modified only the controller card firmware to use a more efficient GCR code called " 6 and 2 encoding". Neither the drive itself nor the physical bit density was changed. This update had the disadvantage of not automatically booting older 13 sector Apple II software. Since the Disk II controller was completely software-operated, the user had total control over the encoding and format so long as it was within the physical limits of the drive mechanism and media. This also allowed software companies to use all sorts of ingenious
copy protection Copy protection, also known as content protection, copy prevention and copy restriction, describes measures to enforce copyright by preventing the reproduction of software, films, music, and other media. Copy protection is most commonly found on ...
schemes. The Shugart SA-400, from which the Disk II was adapted, was a single-sided, 35-track drive. However, it was common for users to manually flip the disk to utilize the opposite side, after cutting a second notch on the diskette's protective shell to allow write-access. Most commercial software using more than one disk side was shipped on such "flippy" disks as well. Only one side could be accessed at once, but it did essentially double the capacity of each floppy diskette, an important consideration especially in the early years when media was still quite expensive. In the Disk II, the full-height drive mechanism shipped inside a beige-painted metal case and connected to the controller card via a 20-pin
ribbon cable A ribbon cable (also known as multi-wire planar cable) is a cable with many conducting wires running parallel to each other on the same flat plane. As a result, the cable is wide and flat. Its name comes from its resemblance to a piece of ribb ...
; the controller card was plugged into one of the bus slots on the Apple's mainboard. The connector is very easy to misalign on the controller card, which will short out a certain IC in the drive; if later connected correctly, a drive damaged this way will delete data from any disk inserted into it as soon as it starts spinning, even write-protected disks such as those used to distribute commercial software. This problem resulted in numerous customer complaints and repairs, which led to Apple printing warning messages in their user's manuals to explain how to properly install the connector. They used different connectors that could not be misaligned in later drives.
DB-19 The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, n ...
adapters for the original Disk II were eventually available for use with Apple's later connector standard. Up to 14 drives could be attached to one Apple II or Apple IIe computer - two drives per controller card, one card per slot, and there were seven usable slots per computer. While the DOS and ProDOS operating systems worked equally well with the card in any of the normal slots (i.e. all except slot 0 of the Apple II/II+ or the special memory expansion slots of the later models), Apple's printed manuals suggested using slot 6 for the first controller card; most Apple II software expects this slot to be used for the main -inch disk drive and fails otherwise. A
Bell & Howell Bell and Howell LLC is a U.S.-based services organization and former manufacturer of cameras, lenses, and motion picture machinery, founded in 1907 by two projectionists, and originally headquartered in Wheeling, Illinois. The company is now ...
version of the Disk II was also manufactured by Apple in a black painted case, which matched the color of the Bell & Howell version of the Apple II Plus, which Apple was already manufacturing.


Disk III

In 1978, Apple intended to develop its own " FileWare" drive mechanism for use in the new Apple /// and
Lisa Lisa or LISA may refer to: People People with the mononym * Lisa Lisa (born 1967), American actress and lead singer of the Cult Jam * Lisa (Japanese musician, born 1974), stylized "LISA", Japanese singer and producer * Lisa Komine (born 1978), J ...
business computers then being developed. They quickly ran into difficulties with the mechanisms, which precluded them from being incorporated in the Apple ///. That machine thus continued to use the same Shugart design as the Disk II. The first variation of the Disk II introduced for the Apple ///, called the Disk III (A3M0004), used the identical drive mechanism inside a modified plastic case with a proprietary connector. With some modification both drives are interchangeable. Though Apple sought to force the purchase of new drives with the Apple ///, many former Apple II users quickly devised a way to adapt their existing and cheaper Disk II drives; however, only one external Disk II was supported in this manner. The Disk III was the first to allow daisy chaining of up to three additional drives to the single 26-pin
ribbon cable A ribbon cable (also known as multi-wire planar cable) is a cable with many conducting wires running parallel to each other on the same flat plane. As a result, the cable is wide and flat. Its name comes from its resemblance to a piece of ribb ...
connector on the Apple ///, for a total of 4 floppy disk drives – the Apple /// was the first Apple to contain a built-in drive mechanism. The
Apple III Plus The Apple III (styled as apple ///) is a business-oriented personal computer produced by Apple Computer and released in 1980. Running the Apple SOS operating system, it was intended as the successor to the Apple II series, but was largely consid ...
changed its 26-pin connector to a
DB-25 The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, no ...
connector, which required an adapter for use with the Disk III.


FileWare

In 1983, Apple finally announced a single and dual external drive (''UniFile'' and ''DuoFile'') implementing the 871-kilobyte " FileWare" mechanism used in the original Apple Lisa, as a replacement for the Disk II & /// drives. However, due to the reliability problems of the Apple-built "Twiggy" drive mechanisms, the products never shipped.


DuoDisk

In 1984, shortly after the introduction of the
Apple IIe The Apple IIe (styled as Apple //e) is the third model in the Apple II series of personal computers produced by Apple Computer. The ''e'' in the name stands for ''enhanced'', referring to the fact that several popular features were now built-in ...
the previous year, Apple offered a combination of two, two third-height, 140-kilobyte Disk II drive mechanisms side-by-side in a single plastic case, called the DuoDisk (A9M0108), which could not be daisy-chained. The unit was designed to be stacked on top of the computer, and beneath the monitor. Each unit required its own disk controller card (as each card could still control only two drives) and the number of units was thus limited to the number of available slots; in practice, few uses of the Apple II computer can make good use of more than two -inch drives, so this limitation mattered little. Originally released with a DB-25 connector to match that of the Apple III Plus, it was the first to adopt Apple's standard DB-19 floppy drive connector.


Disk IIc

The Disk IIc (A2M4050) was a half-height -inch
floppy disk drive 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 ...
introduced by
Apple Computer Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...
in 1984 styled for use alongside the Apple IIc personal computer, the only Apple II to contain a -inch built-in disk drive mechanism. The disk port on the original IIc was only designed to control one additional, external -inch disk drive, and as such, this particular drive omitted a daisy-chain port in back. It was possible to use it on other Apple II models, so long as it came last in the chain of drive devices (due to lacking a daisy-chain port); but since the Disk IIc was sold without a controller card, the Apple IIc computer needing none, it had to be adapted to an existing Disk II controller card in this case. Essentially the same as the full-height Disk II, Apple sold the Disk IIc for US$329, and other companies later sold similar drives for less.


UniDisk and Apple 5.25 Drive

Just over a year after the release of the DuoDisk, Apple introduced the UniDisk (A9M0104) in a plastic case whose styling was similar to that of the DuoDisk. After the release of the UniDisk 3.5 a few months later, the UniDisk was often informally referred to as the "UniDisk 5.25" to distinguish the similarly-named drives. Since the UniDisk could fully replace the Disk II in all its uses, the original Disk II was discontinued at this point. In 1986 a
Platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...
-gray version of the drive named the Apple 5.25 Drive (A9M0107) was introduced alongside the first Platinum-colored computer, the
Apple IIGS The Apple IIGS (styled as II), the fifth and most powerful of the Apple II family, is a 16-bit personal computer produced by Apple Computer. While featuring the Macintosh look and feel, and resolution and color similar to the Amiga and Atari ST ...
. The drive's name was similar to that of the Apple 3.5 Drive, also released with the IIGS. Like the DuoDisk and Disk IIc before them, the UniDisk and Apple 5.25 Drive were half-height disk mechanisms inside an individual drive enclosure. Both drives featured a
daisy chain Daisy chain may refer to: * Daisy chain, a garland created from daisy flowers * Daisy chain (climbing), a type of strap * Daisy chain (electrical engineering), a wiring scheme * Daisy chain (fishing), a type of fishing lure * Daisy chain (knot), ...
pass-through port. While the drives were essentially interchangeable among Apple II computers, both with each other and with the earlier drives, minor electrical differences dictated that only the Apple 5.25 Drive could be used with the later (ROM 3) version of the Apple IIGS and with the Apple IIe Card on a
Macintosh LC The Macintosh LC is a personal computer designed, manufactured, and sold by Apple Computer, Inc. from October 1990 to March 1992. Overview The first in the Macintosh LC family, the LC was introduced with the Macintosh Classic (a repackaging o ...
.


-inch drive

In 1984, Apple had opted for the more modern, Sony-designed -inch floppy disk in late-model Lisas and the new
Apple Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
. Accordingly, they attempted to introduce a new -inch 800-kilobyte floppy disk format for the Apple II series as well, to eventually replace the 140-kilobyte Disk II format. However, the external UniDisk 3.5 drive required a ROM upgrade (for existing Apple IIc machines; new ones shipped after this time had it from the factory) or a new kind of disk controller card (the so-called "Liron Card", for the Apple IIe) to be used. The much larger capacity and higher bitrate of the -inch drives made it impractical to use the software-driven Disk II controller because the 1-megahertz
6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit microprocessor that was designed by a small te ...
CPU in the Apple II line was too slow to be able to read them. Thus, a new and much more advanced (and correspondingly expensive) hardware floppy controller had to be used. And many original Apple IIs could not use the new controller card at all without further upgrades. Also, almost all commercial software for the Apple II series continued to be published on -inch disks which had a much larger installed base. For these reasons the -inch format was not widely accepted by Apple II users. The Apple 3.5 Drive used the same 800-kilobyte format as the UniDisk 3.5", but it did away with the internal controller, which made it cheaper. Unlike all earlier Apple II drives, it was designed to work with the Macintosh too, and among Apple II models, it was compatible only with the
Apple IIGS The Apple IIGS (styled as II), the fifth and most powerful of the Apple II family, is a 16-bit personal computer produced by Apple Computer. While featuring the Macintosh look and feel, and resolution and color similar to the Amiga and Atari ST ...
and the Apple IIc+ models, which both had a faster main CPU. On the Apple IIGS, whose improved audiovisual capacities really demanded a higher-capacity disk format as well, the -inch format was accepted by users and became the standard format. Though Apple eventually offered a 1.44-megabyte SuperDrive with matching controller card for the Apple II series as well, the -inch Disk II format drives continued to be offered alongside the newer -inch drives and remained the standard on the non-IIGS models until the platform was discontinued in 1993. Officially, the following -inch drives could be used on the Apple II: *Apple 3.5" External (A9M0106) – Designed for Apple IIs with the Liron or Superdrive controller or all Macintoshes with an external 19-pin floppy port (Mac 512s must be booted from the internal 400-kilobyte drive with the HD20 INIT, which provides HFS file system support – the Macintosh 128K will not work with this). The drive can be daisy chained, however this feature is not supported on the Macintosh. *Unidisk 3.5" Drive (A2M2053) – Designed for Apple IIs with the Liron or Superdrive controller (not compatible with Macintoshes) Recommended only for 8-bit Apple IIs as the A9M0106 operates faster on the IIGS *Apple FDHD External (G7287) – Supports 720-kilobyte/1.44-megabyte MFM floppy disks in addition to 800-kilobyte GCR. Designed for Apple IIs and Macs with the Superdrive controller, but will also work on machines with the older 800-kilobyte controller (as an 800-kilobyte drive – note that the G7287 is not compatible with the Mac 128/512) The 400-kilobyte and 800-kilobyte Macintosh external drives (M0130 and M0131) are incompatible with standard Apple II controllers as they do not support the drives' automatic disk-eject feature, although they could be used with third-party controllers.


Apple PC 5.25" Drive

There is one -inch drive made by Apple that is completely incompatible with all the drives named above. In 1987, Apple sought to better compete in the IBM dominated business market by offering a means of cross-compatibility. Alongside the release of the Macintosh SE &
Macintosh II The Macintosh II is a personal computer designed, manufactured, and sold by Apple Computer from March 1987 to January 1990. Based on the Motorola 68020 32-bit CPU, it is the first Macintosh supporting color graphics. When introduced, a basic sy ...
, Apple released the Apple PC 5.25" Drive which required a separate custom PC 5.25 Floppy Disk Controller Card, different for each Mac model. It is the only -inch drive manufactured by Apple that can be used by the Macintosh. This drive was for use with industry standard double-sided -inch 360-kilobyte formatted flexible disks. It was similar in appearance to the Disk IIc. Through the use of a special Macintosh
Apple File Exchange Apple File Exchange (AFE) is a utility program for Apple Macintosh computers. It was included on the Apple "Tidbits" or "Install 2" disk in system versions 7.0 through 7.1. In System 7.5 (released in 1994), it was replaced by PC Exchange. Apple ...
utility shipped with it, the drive could read files from, and write files to, floppy disks in
MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
formats. Software "translators" could convert documents between
WordStar WordStar is a word processor application for microcomputers. It was published by MicroPro International and originally written for the CP/M-80 operating system, and later written also for MS-DOS and other 16-bit PC OSes. Rob Barnaby was the so ...
and
MacWrite MacWrite is a WYSIWYG word processor application released along with the first Apple Macintosh systems in 1984. Together with MacPaint, it was one of the two original "killer applications" that propelled the adoption and popularity of the GUI i ...
formats, among others. The drive is incompatible with all Apple II computers and the Apple IIe Card for the
Macintosh LC The Macintosh LC is a personal computer designed, manufactured, and sold by Apple Computer, Inc. from October 1990 to March 1992. Overview The first in the Macintosh LC family, the LC was introduced with the Macintosh Classic (a repackaging o ...
as well; it also does not allow a Macintosh to read from or write to -inch Apple II-formatted disks. This drive was made obsolete by the industry-wide adoption of -inch disks and was replaced by the -inch Apple FDHD Drive, which could read and write every existing Macintosh,
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
and
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
format, and the Apple II ProDOS format as well.


Disk II cable pinout

This table shows the pinout of the original 1979 Disk II controller and newer 1983 Uni/Duo Disk I/O controller (655-0101). The circuitry of these two controllers are identical. The Disk II header pin numbering is per the Disk II controller card silkscreen and the circuit schematic given in the DOS 3.3 manual. The Uni/Duo Disk D-19 pinout is taken from the ''Apple //c Reference Manual, Volume 1''. NOTES: *Active low signals are suffixed with a "*" *Since most signals are shared with both drive 1 and drive 2, the logic in each drive uses the ENABLE* signal to activate appropriately. **Pin 14 for Disk II drive 1 and drive 2 have separate enable signals (14a and 14b) **Pin 17 for Uni/Duo Disk is chained to first drive (drive 1) and second drive (drive 2) is enabled via other logic in the first drive. *The EXTINT* signal is not present on the Disk II controller card. In the Apple //c computer, it is routed to the DSR* signal of the internal 6551 ACIA (UART) chip.


See also

*
List of Apple drives {{unfocused, date=February 2016 A list of all Apple internal and external drives in chronological order of introduction. Floppy disk drives * Disk II * Disk III * Apple FileWare, Apple "Twiggy" FileWare * Disk IIc * 400K Drive (internal) * Ma ...


References


External links


Apple II History - Chapter 5 (Disk II)







Disk II Controller hardware article


an

at comp.sys.apple2 FAQ mirror


Apple floppy drive schematics

The untold story behind Apple's $13,000 operating system
{{Apple hardware Apple II peripherals Apple II family Floppy disk drives