IBM Model F
Model F was the designation given by IBM to their buckling spring over capacitive contact keyboards, manufactured by IBM and Lexmark between 1981 and 1994. The most well known Model F keyboards are the IBM Personal Computer keyboard and the IBM Personal Computer AT keyboard, but were also made for a wide variety of other IBM computers and terminals, and some of the IBM Electronic Typewriter family.
First appearing in the System/23 Datamaster of 1981, the Model F design was used in most keyboards that IBM produced in the 1980s. However, by 1983, IBM had designed the much cheaper and easier to manufacture Model M keyboard design, and after the AT Model F, IBM began using the Model M with its buckling spring over membrane switching system instead. Model F keyboards continued to be produced as late as 1994 in the case of certain terminal keyboard variants. Unlike the Model M, the Model F designation was not always shown on the back of the keyboard. In some cases, it can be found on the label on the backplate of the keyboard assembly. On some other keyboards, it is completely absent.
With the exception of the IBM PC AT, most Model F variants will need some sort of active adapter to be reliably used with a modern PC.
Common Design Features
The Model F was the first design to make use of IBM's buckling spring mechanism. It was a follow on to the earlier Beam Spring keyboards. In addition to being cheaper, they were also more compact and lighter than their predecessors – to the extent that IBM's sales literature described the keyboards as "low profile" and "ergonomic". The Model F made use of the same design of capacitive contacts as the beam spring keyboards, and thus many early Model F designs were buckling spring versions of beam spring keyboards, although the exact electronics differed slightly.
The internal assembly of a Model F keyboard consisted of a metal backplate, and a painted metal upper plate, both of which were curved in shape. In the Model F, the PCB was flexible, and thus was also curved when attached to the backplate. Whereas the curve in many keyboards were (and are) simulated by different keycap profiles, the curve was actually built into the Model F design. One advantage of this approach was that all of the keycaps on the keyboard were of the same shape, size and profile.
The springs with their attached hammers (the 'Pivot Plate Assemblies' in IBM terminology) were housed in removable barrel modules, which slid into slots on the upper plate. The upper assembly plate was lined on the inside with a layer of foam. The upper and lower plates were held together with a series of interlocking tabs, and one tab from the top plate folded over the bottom plate. Depending on the exact design of the keyboard, the modules were either held in place by a stud beneath the barrel, or a tab that protruded from the bottom right hand side of the barrel. The former was common in stabilizer free (except for space bar) keyboards, whereas the latter was used in ones with stabilizer bars on the large keys.
Model F keycaps were the same design as those used in the later Model M designs. Single part keycaps were standard, but the 122-key PC 3270 and 3179 terminal keyboards were the first to use the double part keycaps, as a means of offering customization on terminals.
IBM System/23 Datamaster Keyboard
The original Model F keyboard, which appeared on the IBM System/23 Datamaster, released one month before the IBM PC. It consisted of an 83-key keyboard mounted internally in the Datamaster unit. The physical and functional layout was similar to that of the IBM 5251 terminal. The engineers who worked on the Datamaster later worked on the PC, and convinced their superiors to use the Datamaster keyboard for the PC, and thus it spawned a number of variants used in a number of other IBM computers.
IBM Personal Computer keyboard
The keyboard of the IBM PC 5150 of 1981. Commonly referred to as the "PC XT" keyboard, although it predates the XT. It was based on the Datamaster keyboard, except mounted in an external casing, and using a unidirectional serial connection with a DIN-5 connector to attach to the PC. When the PC was launched, its keyboard won acclaim for being one of the highest quality personal computer keyboards in terms of type feel, but was also criticized for having a poor layout, with a large number of oddly shaped keys squashed together. The US English layout variant had the part number 1501100
IBM Industrial PC Keyboard
The keyboard of the IBM 5531 Industrial PC, released in 1984, was a version of the standard PC/XT keyboard in a green/grey casing. Some had black IBM logos instead of the standard silver. Other than the cosmetic changes, they were internally identical.
IBM 5531 Keyboard. This "Frankenboard" example has had the buckling spring internals replaced by a third party assembly, thus the non standard keycaps and switches.
IBM CS/9000 Keyboard
The CS/9000 (also known just as the System 9000) of 1982 was a laboratory computer based around a Motorola 68000 CPU. Its keyboard was electronically interchangeable with that of the PC and PC/XT. It's not clear whether it had the exact same functional layout as the regular PC keyboard.
IBM Portable Computer Keyboard
The 5155 Portable PC was a briefcase-style portable computer released in 1984. It used the standard PC/XT keyboard with some modifications - the casing was different as the keyboard attached over the top of the case when not in use. It used an RJ-11 connector and a less thick cable to attach to the computer (it also came with an adapter to DIN-5 so that it could be used with a standard PC). Unusually, the keyboard featured no backplate, probably to reduce weight. US layout had part number 6450300.
IBM EMR Keyboard
The EMR keyboard appears to have been used in specialized TEMPEST-hardened versions of IBM PCs (i.e. computers that have been specially designed not to emit any electromagnetic signals that may be used by an eavesdropper to access the data on the system) It appears to be a standard PC/XT Model F with a different cable and connector, and with shielding around the controller card inside the keyboard. Some examples have been seen with Caps Lock located to the left of A, Ctrl located to the left of the spacebar, and Alt to the right of the spacebar. Examples seen have been for a PC/XT style system, but it is possible that there are variants of the 122-key terminal, AT, and Model M Enhanced keyboards that had similar cable/connector modifications. The EMR keyboard used a DIN connector with a shield cable, whereas the EMR II keyboard used a 4-pin D-SUB connector.
IBM 5291 Keyboard
Another descendant of the Datamaster keyboard, the keyboard of IBM's 5291 terminals used the same keyboard mounted in a larger casing than the one used in the PC/XT keyboard. It used the same functional layout as the 5251 terminal keyboard, and attached to the terminal with a 15-pin connector. An unusual feature of this keyboard is the three-stage keyboard feet it uses. US layout variants had the part numbers 4176191 or 1397950.
IBM 3178 Keyboards
The IBM 3178 was a low cost 3270 terminal based on the design of the 3101 launched in 1983. Much like the 3278, it had an array of different 75-key and 87-key keyboard options, and used the same physical and functional layouts as its beam spring predecessors. The keyboard had no feet, and the 75-key variants used the same size casing as the 87-key ones, but with the right hand keypad area covered over. The label on the back of the keyboards are designated with the model of the terminal that they are intended to be used with - C1 through C4. Part numbers were of the form 56409xx depending on version.
IBM 3101 Model F Keyboard
In 1983, IBM replaced the beam spring keyboard of the 3101 with a Model F keyboard. It consisted of the 3178 keyboard with the functional layout of the 3101. This unit was electronically interchangeable with the older beam spring 3101 keyboard.
IBM 3104 Keyboard
The 3104 was a low cost mainframe terminal. It had a limited subset of the 3178's keyboard options, and they had their own part numbers. It is unclear whether or not they were compatible with the keyboards used on the 3178.
IBM Personal Computer AT keyboard
The Personal Computer Advanced Technology (PC AT), released in 1984, was the successor to the IBM PC and XT. It featured a revamped keyboard design, which was probably the final Model F keyboard design before the first Model Ms appeared later on in the year. The layout was modified to address criticisms of the earlier PC keyboard, and somewhat resembled the layout used on the IBM Displaywriter keyboard. The communications protocol between the keyboard and computer was also redesigned, it used a bi-directional protocol which supported the use of lock lights on the keyboard. Despite being incompatible with the older PC keyboard, it still used the same DIN-5 connector. The AT keyboard protocol became standard and is compatible with that used on PS/2 keyboards. The US layout variant had the part number 6450200.
IBM Displaywriter Model F Keyboard
In 1982, IBM made available a Model F keyboard for the Displaywriter in addition to the original Beam Spring variants. It was marketed as a "low profile" and "ergonomic" alternative to the original Beam Spring keyboards. The keyboard was only available in the 84-key, 96-character layout, and not the less common 82-key, 92-character variant. The Displaywriter Model F used the same two-stage feet as some of the terminal keyboards, and featured an all-white key colour scheme.
IBM 122-key Model F Keyboards
The 122-key keyboards used originally for the PC 3270 (an XT with terminal emulation software and hardware) and later the 3179 and 3180 terminals. Part number 611034x, depending on version, layout, and whether it was for use with an emulator or actual terminal. It used a 240-degree DIN-5 connector. The layout was arguably inspired by the DEC LK-201, and seems to have been the basis for the layout of the later Model M Enhanced Keyboard. They can be distinguished from the Model M 122-key keyboards by their black metal underside (as opposed to plastic on the Model M equivalents.) The PC terminal emulator keyboards are the only keyboards that actually make use of all 122 keys. Most (if not all) of the dedicated terminal keyboards have a number of blank keys which do nothing when pressed.
IBM 104-key Model F Keyboards
The 104-key Model F was a less common variant of the 122-key terminal keyboard which lacked a numeric keypad. It was primarily associated with two types of IBM terminal – the IBM 5085 Graphics Display (part number 6016730), and the IBM 3290 Display Station (part number 1387033). The variant for the 5085 had a speaker two D-SUB connectors at the back – one to connector to the terminal, and the other to interface with other peripherals for the 5085. The 3290 variant used the regular 240-degree DIN-5 connector seen on most IBM terminals of the time and lacked a speaker. IBM later offered a rubber dome 104-key keyboard (part numbers 73X38xx) for some of their terminals which was manufactured by Micro Switch.
IBM 4980 Keyboard
The IBM 4980 was a terminal for the IBM Series/1 minicomputer, which used a 127-key Model F keyboard. It was otherwise similar to the regular 122-key keyboard, but featured additional keys so that the keyboard's layout was more similar to the beam spring keyboards used on older Series/1 terminals (the 122-key keyboards even have the contacts for the extra keys present on the 127-key layout).
The design and layout of IBM Model F—in particular the AT version—was widely copied by other keyboard manufacturers both in the US and the Far East.