The Invention of the Floppy Disk

The floppy disk was invented by IBM engineers led by Alan Shugart.

3 1/2 Inch Diskette
3 1/2 Inch Diskette. freephotos

In 1971, IBM introduced the first "memory disk", as it was called then, or the "floppy disk" as it is known today.

8-inch Floppy Disk

The first floppy was an 8-inch flexible plastic disk coated with magnetic iron oxide; computer data was written to and read from the disk's surface.

The nickname "floppy" came from the disk's flexibility. The floppy disk was considered a revolutionary device in the "History of Computers" for its portability which provided a new and easy physical means of transporting data from computer to computer.

Inventor Alan Shugart

The "floppy" was invented by IBM engineers led by Alan Shugart. The first disks were designed for loading microcodes into the controller of the Merlin (IBM 3330) disk pack file (a 100 MB storage device). So, in effect, the first floppies were used to fill another type of data storage device. Overnight, additional uses for the floppy were discovered, making it the hot new program and file storage medium.

How Does a Floppy Work?

A floppy is a circle of magnetic material similar to other kinds of recording tape such as cassette tape; one or two sides of the disk are used for recording. The disk drive grabs the floppy by its center and spins it like a record inside its housing. The read/write head, much like the head on a tape deck, contacts the surface through an opening in the plastic shell, or envelope. The first Shugart floppy held 100 KBs of data.

  • First-hand account of how the operating system for the 8-inch disk was written.

    5 1/4-inch Floppy Disk

    In 1976, the 5 1/4" flexible disk drive and diskette was developed by Alan Shugart for Wang Laboratories. Wang wanted a smaller floppy disk and drive to use with their desktop computers. By 1978, more than 10 manufacturers were producing 5 1/4" floppy drives that stored up to 1.2MB (megabytes) of data.

    One interesting story about the 5 1/4-inch floppy disk is how the size was decided. Engineers Jim Adkisson and Don Massaro were discussing the size with An Wang of Wang Laboratories. The trio just happened to be doing their discussing at a bar. ​Wang motioned to a drink napkin and stated "about that size" which happened to be 5 1/4-inches wide.

    3 1/2-inch Floppy Disk

    In 1981, Sony introduced the first 3 1/2" floppy drives and diskettes. These floppies were encased in hard plastic, however, the name stayed the same. They stored 400kb of data, and later 720K (double-density) and 1.44MB (high-density).

    Post Floppy Disk

    For the most part, recordable CDs and DVDs, and flash drives have replaced floppies as the means of transporting files from one computer to another computer.

    Next Chapter > Robert Metcalfe, Xerox, & The Ethernet

    The following interview was done with Richard Mateosian who developed a floppy disk operating system for the first "floppies". Richard Mateosian is currently a review editor at IEEE Micro Berkeley, CA.

    About: Tell us about working on the floppy disk.

    Richard Mateosian The disks were 8 inches in diameter and had a capacity of 200K. Since they were so large, we divided them into four partitions, each of which we regarded as a separate hardware device -- analogous to a cassette drive (our other main peripheral storage device).

    We used floppy disks and cassettes mostly as paper tape replacements, but we also appreciated and exploited the random access nature of disks.

    Our operating system had a set of logical devices (source input, listing output, error output, binary output, etc.) and a mechanism for establishing a correspondence between these and the hardware devices. Our applications programs were versions of HP assemblers, compilers, and so forth, modified (by us, with HP's blessing) to use our logical devices for their I/O functions.

    The rest of the operating system was basically a command monitor. The commands had mainly to do with file manipulation. There were some conditional commands (like IF DISK) for use in batch files. The entire operating system and all of the application programs were in HP 2100 series assembly language.

    The underlying system software, which we wrote from scratch, was interrupt driven, so we could support simultaneous I/O operations, such as keying in commands while the printer was running or typing ahead of the 10 character per second teletype.

    The structure of the software evolved from Gary Hornbuckle's 1968 paper "Multiprocessing Monitor for Small Machines" and from PDP8-based systems, I worked on at Berkeley Scientific Laboratories (BSL) in the late 1960s. The work at BSL was largely inspired by the late Rudolph Langer, who improved significantly on Hornbuckle's model.