In 1967, IBM tasked their San Jose, California development laboratory to develop a reliable and inexpensive system for loading microcode into their System/370 mainframes in a process called Initial Control Program Load (ICPL). The System/370 was IBM’s first computer system family to make extensive usage of volatile read/write semiconductor memory for microcode, so for most models, whenever the power was turned on, the microcode had to be loaded (System/370’s predecessor, System/360, generally used non-volatile read-only memory for microcode). IBM also wanted inexpensive media that could be sent out to customers with software updates.
IBM Direct Access Storage Product Manager, Alan Shugart, assigned the job to David L. Noble, who tried to develop a new-style tape for the purpose, but without success. The project was reassigned to Donald L. Wartner, 23FD Disk Drive manager, and Herbert E. Thompson, 23FD Disk manager, along with design engineers Warren L. Dalziel, Jay Brent Nilson, and Ralph Flores; and that team developed the IBM 23FD Floppy Disk Drive System (code name Minnow). The disk is a read-only, 8-inch-diameter (200 mm) flexible diskette called the “memory disk” and holding 80 kilobytes of data. Initially the disk was bare, but dirt became a serious problem so they enclosed it in a plastic envelope lined with fabric that would remove dust particles. The Floppy Disk Patent #3,668,658 was issued on June 6, 1972 with named inventors Ralph Flores and Herbert E. Thompson. The Floppy Disk Drive Patent #3,678,481 was issued July 18, 1972 with named inventors Warren L. Dalziel, Jay. B. Nilson, and Donald L. Wartner. IBM introduced the diskette commercially in 1971.
The new device first shipped in 1971 as the 23FD, the program load component of the 2835 Storage Control Unit. and then as a standard part of most System 370 processing units and other IBM products. Internally IBM used another device, code named Mackerel, to write boot disks for distribution to the field.
Alan Shugart left IBM and moved to Memorex where his team shipped the Memorex 650 in 1972, the first commercially available read-write floppy disk drive. The 650 had a data capacity of 175 kB, with 50 tracks, 8 sectors per track, and 448 bytes per sector. The Memorex disk was “hard-sectored”, that is, it contained 8 sector holes (plus one index hole) at the outer diameter (outside data track 00) to synchronize the beginning of each data sector and the beginning of a track.
In 1973, IBM shipped its first read/write floppy disk drive, the 33FD, as a component of the 3740 Data Entry System, code named “IGAR”, designed to directly replace IBM’s punched card (“keypunch”) data entry machines. A significant feature of IBM’s read/write disk media was the use of a Teflon-lubricated fabric liner to lengthen media life. In 1976, media supplier Information Terminals Corporation enhanced resilience further by adding a Teflon coating to the magnetic disk itself. The new system used a different recording format that stored up to 250¼ kB on the same disks. Drives supporting this format were offered by a number of manufacturers and soon became common for moving smaller amounts of data. This disk format became known as the Single Sided Single Density or SSSD format. It was designed to hold just as much data as one box of 2000 punch cards. The disk was divided into 77 tracks of 26 sectors (a total of 2002 sectors), each holding 128 bytes.
8-inch disk drive with diskette (3½-inch disk for comparison)
When the first microcomputers were being developed in the 1970s, the 8-inch floppy found a place in them as one of the few “high speed, mass storage” devices that were even remotely affordable to the target market (individuals and small businesses). The first microcomputer operating system, CP/M, originally shipped on 8-inch disks. However, the drives were still expensive, typically costing more than the computer they were attached to in early days, so most machines of the era used cassette tape instead.
Also in 1973, Shugart founded Shugart Associates which went on to become the dominant manufacturer of 8-inch floppy disk drives. Its SA800 became the industry standard for form factor and interface.
In 1976, IBM introduced the 500 KB Double Sided Single Density (DSSD) format, and in 1977 IBM introduced the 1–1.2 MB Double Sided Double Density (DSDD) format.
Other 8-inch floppy disk formats such as the Burroughs 1 MB unit failed to achieve any market presence.