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Disk II

The Disk II Floppy Disk Subsystem, often stylized as disk ][, is a 5¼-inch floppy disk drive designed by Steve Wozniak and manufactured by Apple Computer. The Disk II was designed specifically for use with the Apple II series to replace the slower cassette tape storage.


Apple Checkbook 1 cassette

The slow speed of this cassette led to the creation of the Disk II.

Apple did not originally offer a disk drive for the first Apple II, which used cassette tape storage like other microcomputers of the time. Early Apple investor and executive Mike Markkula asked co-founder Steve Wozniak 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.[1] Wozniak knew nothing about disk controllers, but while at Hewlett-Packard he had designed a simple, five-chip circuit to operate a Shugart Associates drive.[2]

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.[3] The external case was designed by Jerry Manock.[4]

The Disk II went on sale in June 1978 at a retail price of US$495 for pre-orders. It was later sold for $595, with a controller card that could control up to two drives, and cable. These floppy drives cannot be used with any Macintosh without an Apple IIe Card.


  • Disk II — a full height mechanism designed for the early Apple II series.
  • Disk III — same internal mechanism, but used a proprietary connector for the Apple III.
  • DuoDisk — a pair of 2/3 height mechanisms in a single case.
  • Disk IIc — a single 1/2 height mechanism designed for the Apple IIc
  • UniDisk 5.25" — a single 2/3 height mechanism in a new case to match the aesthetics of the Apple IIe


Apple originally developed a proprietary 5.25-inch FileWare drive (nicknamed "Twiggy") for the Lisa and Macintosh. However, after problems with reliability, a smaller 3.5-inch floppy mechanism from Sony was adopted.[5]


  1. Markoff, John. "An 'Unknown' Co-Founder Leaves After 20 Years of Glory and Turmoil", The New York Times, September 1, 1997. Retrieved on February 4, 2011. 
  2. "The Apple Story / Part 2: More History and the Apple III", BYTE, UBM Technology Group, January 1985, p. 167. 
  3. Terdiman, Daniel (April 3, 2013). The untold story behind Apple's $13,000 operating system.
  4. Jerrold C. Manock. Manock Comprehensive Design, Inc.. Retrieved on 27 July 2011.
  5. Quick, Hide In This Closet! by Andy Hertzfeld, Folklore. 1983-08.

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