The 8-inch disk


In 1967, IBM gave their San Jose, California storage development center a task 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. Noble's team developed a read-only, 8-inch-diameter (200 mm) flexible diskette they called the "memory disk", holding 80 kilobytes of data. The original 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. IBM introduced the diskette commercially in 1971.
The new device, developed under the code name Minnow and shipped as the 23FD, was a standard part of System 370 processing units (IBM internally used another device, code named Mackerel, to write boot disks for distribution to the field). It also was used as a program load device for other IBM products such as the 2835 Storage Control Unit.

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