Happy 45th Birthday to the IBM PC and Model F/XT

The IBM PC's 45th anniversary retrospective by Admiral Shark's Keyboards traces the Model F's capacitive buckling spring mechanism back to the IBM System/23 Datamaster (5322), establishing it as the earliest confirmed Model F implementation to reach market. The mechanism, designed by Richard Hunter Haris under U.S. patent 4,118,611, works by compressing a metal coil spring until it buckles, pivoting a capacitive plate atop a capacitance-sensing PCB called a "pad card." This corrects or refines the assumption that the Model F debuted with the PC itself.

The PC's type number, 5150, places it in a lineage stretching back through the 5120, 5110, and 5100 Computing Systems to the 1973 SCAMP prototype developed at IBM's Palo Alto Scientific Center. William C. Lowe, then an executive in IBM's General Systems Division, was instrumental in fostering that prototype. The 5100 was called a "personal computer" by some in the media but was expensive and not widely accessible.

Before settling on the PC's final design, IBM explored several dead ends. Designer Tommy R. Hardy conceptualized the "Yellow Bird" (1976) and "Aquarius" (1977) personal computer ideas, with Aquarius reaching pre-production prototype before being dismissed over concerns about its bubble memory modules. IBM also considered acquiring Atari and using the Atari 800 as the basis for an IBM personal computer, with Hardy designing a pearl-white IBM-branded 800 concept, but this idea went no further.

The Datamaster's influence on the PC extends beyond its keyboard. Development began in February 1978 with hardware ready by July 1980, but its launch was delayed a full year, until July 1981, just one month before the PC, because IBM decided to align the Datamaster's BASIC with the IBM System/34 midrange computer's implementation. IBM engineer David J. Bradley, who worked on Datamaster, recalled this delay. The 5322's styling is attributed to Tommy R. Hardy via U.S. design patent 275,285, filed February 4, 1980.

The Model F keyboard family expanded across IBM's flagship keyboards for the first half of the 1980s, all using the same capacitive buckling spring mechanism. The 5322 keyboard layout derived from the Model B-based IBM 5251/5252 Display Station Typewriter Keyboard, IBM's most common pre-Datamaster keyboard design. This lineage shows how IBM adapted existing business terminal keyboard designs for the personal computer era rather than designing from scratch.