IBM's fourth generation of keyboards
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The Model F (known as Keyboard F internally) constitutes IBM's fourth generation of keyboards created in 1981 and produced until 1996. The Model F family shares strong design traits between its members much like the previous Model B family but unlike the following Model M family, as Model Fs are all buckling spring keyboards with capacitance sensing with a similar sort of internal assembly. In terms of recognition, Model Fs are often overshadowed by their successor family - but whilst Model F keyboard layouts are generally more archaic than many Model M layouts, Model Fs make up for it with their overall superior reliability and technical benefits both provided by the use of capacitance-sensing PCBs instead of membrane assemblies. The Model F's quality auditory and tactile feedback helped cement the original IBM PC as a quality and popular machine and amongst people who have tried both Model F and Model M keyboards, you'd be hard-pressed to find someone who didn't prefer the key-feel of Model Fs.
In a nutshell, the Model F was the first group of keyboards to employ buckling spring key-switches. The idea of buckling springs by IBM was first patented as the "catastrophically buckling compression column switch and actuator" in 1971 and was invented by Richard Hunter Harris, the man also partially responsible for inventing the beam spring key-switch of the previous Model B family. The original patent as-is was never employed on an actual production keyboard but it establishes the basic premise of a buckling spring used in a keyboard switch design and the goal of combining tactility, actuation, pre-travel and return force in one spring. The Model Fs actually use the 1977-patented IBM "buckling spring torsional snap actuator" switch, a refinement of one of the three types of designs described in the original 1971 patent. The first Model F keyboard assembly can be found in July 1981's IBM System/23 Datamaster computer and came in two forms; the more familiar integrated keyboard assembly (IBM 5322 "desktop" type) and the rarer separate keyboard unit (IBM 5324 "floortop" type). Both had 83 keys.
A month after the Datamaster's launch, IBM released the original IBM Personal Computer (5150) that quickly far eclipsed the earlier system. The 5150 is the ancestor of all modern "x86" PCs, but the system's initial success was undoubtedly aided by its included keyboard - the IBM PC Keyboard. In January 1982, Byte Magazine said "it is, by none, the best keyboard on any microcomputer". Today, this keyboard is referred to as the "Model F/XT" after March 1983's IBM PC/XT (5160) that also used this keyboard as a way to contrast it against later models. Its internal keyboard assembly is the same as the Datamaster's except its electronics are different.
Outside of PCs, Model Fs also became IBM's keyboard of choice for its terminal and enterprise systems for the next 4 years. In January 1982, IBM released the 5291 Display Station featuring a keyboard unit very similar to the IBM 5324 Keyboard but slightly smaller and featuring its characteristic three-setting riser-style feet. This feet arrangement and its size gave it the nickname "bigfoot". By Q4 1982, IBM developed three new Model F keyboard assemblies for use with the IBM 4704 Display Terminal, a part of the IBM 4700 Finance Communication System. IBM first released the 50-key Model 100 Functional Keypad for the 4704-1 in October 1982, which was closely followed by the 62-key Model 200 Alphameric Keyboard and 77-key Model 300 Expanded Alphameric Keyboard in December 1982. Around a year later, the 107-key Model 400 Administrative Keyboard arrived for the 4704-2. All four IBM 4704 keyboards are known for their cast zinc outer casing, making the Model 400 the heaviest known Model F but even the smaller keyboards are heavy by general keyboard standards. Announced in March 1983 and shipped starting in April 1983, the IBM 3178 Display Station was released as a cheaper replacement for the earlier IBM 3278 Display Station and came with two models with slightly different keyboards - 3178-C1 with a 75-key data entry keyboard and 3178-C2 with an 87-key typewriter keyboard respectively. C1 and C2 would be followed by a 3178-C3 the following quarter and a 3178-C4 by 1985, both with 87-key EBCDIC typewriter keyboards. All IBM 3178 keyboards are known for having solenoids inside.
Also in 1983, Model Fs became the platform of significant keyboard layout development with the 104-key and 122-key terminal keyboards, both technically in the lineage of the Model B-based IBM 4978 122-key Keyboard. The 104-key "function key keyboard" (aka, "unsaver") was announced in March 1983 and first shipped in July 1983 with the IBM 3290 Informational Panel, crucially sporting a layout very close to the modern ISO layout used by many regional layouts outside the United States. The "unsaver" also introduced IBM scancode set 3. Contrary to common belief, the 122-key Model F arrived later, being announced in October 1983 and made available by Q1 1984 for the IBM 3270 Personal Computer (5271). The "F122" added an 18-key numeric keypad area to the 104-key design and would later be followed on and developed further by four subsequent 122-key Model M types.
After 2 years of terminal keyboard releases, IBM finally released a new PC-orientated Model F in the form of an F/XT variant for the IBM Portable Personal Computer (5155) in February 1984. The 5155 was a luggable version of the PC/XT, thus it made sense the F/XT was reused for it. The internal assembly was largely the same mechanically and electronically, although 5155 F/XTs have an aluminium backplate instead of steel likely to reduce weight. The entire case is also plastic and the keyboard has a compartment for the cable to be stored in when the keyboard is folded up against the front of the host system. In August 1984, IBM introduced the last wholly new Model F design for the IBM Personal Computer/AT (5170). Technically speaking, this so-called Model "F/AT" represented a big step towards the now-standard PC keyboard design with its introduction of the ANSI-style large left shift key, separated numeric keypad and LED lock-lights to the IBM keyboard family. It's also known for introducing IBM scancode set 2 to keyboards, which out of the three classic IBM scancodes turned out to have the most 'staying power' as even some desktop PCs today still support it via a PS/2 port.
After 1984, no new Model F assembly designs were introduced due to the family being supplanted by the then-new Model M family. Production for standard PC-orientated Model Fs was terminated by the end of the 1980s, however, some Model F keyboards remained in production at least as late as 1994. The 104-key Model F was produced as late as 1992 by IBM United States, the 122-key Model F for the IBM 3270 PC was withdrawn from marketing in August 1994, and the 5291 Model F was produced as late as 1994 by Lexmark (the company formed by IBM's divesture of their US-based keyboard, typewriter and printer production at Boulder, Colorado and Lexington, Kentucky in 1991). Evidence for production after 1994 is minimal, but it's said Lexmark was at least refurbishing 5291 Model Fs as late as 1996 (despite erroneously identifying them as "Model M" on their rear label). There is no evidence Unicomp ever produced Model Fs, thus 1996 is likely the last possible year of Model F production.
All Model F keyboards sport a flexible capacitance-sensing PCB at the centre of their inner keyboard assembly. IBM referred to these PCBs as pad cards and they're made up of many pairs of capacitive contacts that the rest of the key-switch mechanisms (the rockers on the bottom of the buckling springs) are held above. When the above switch mechanism moves closer to the contacts, a change in capacitance is measured and eventually registers a key-press when the capacitance reaches a certain threshold. This is in fact inverse to how the previous Model B keyboard family's beam spring switches operated, which rested at high capacitance and registered key-presses when the capacitance diminishes when its mechanism (the beam spring's capacitive plate) is raised from the pad card. The use of capacitance sensing allows for N-key rollover (provided the rest of the controller and possible hosts support it) and is extremely reliable.
More information: IBM buckling spring#Capacitive
Buckling springs take the form of a spring that when pressed deforms (buckles) in a specific way that allows a flipper (also called rocker or hammer) to hit the circuit underneath to make a connection. In the case of Model F keyboards, pressing the switch will cause the flipper to rest atop a pair of capacitive contact pads and register a key-press. The flipper itself is made of a capacitive material. This contrasts the buckling springs found on the later Model M keyboards that when buckling the flipper physically bridges two contacts on a membrane assembly.
Buckling springs are a clicky-tactile switch considered by some to be the quintessential good clicky switch. The properties of both features are rather unique as there are seldom switches that feature a similar mechanism. It is best described as having a crisp, pingy click that perfectly matches the point of key-switch actuation, and having tactility suited for typing but also not over the top. Buckling springs on Model Fs are rated for 100 million key presses and are also on the heavier feeling side of switches, although they are a tad lighter and crisper than Model M buckling springs.
All Model F keyboards are not monoblocks, instead featuring an inner keyboard assembly separate from the outer case. The typical Model F keyboard assembly is a sandwich of the following distinct layers:
Model F assemblies are secured together with several tabs surrounding the edges of the assembly, contrasting the plastic rivets most Model Ms employ. This means that the main longevity concern with Model Ms does not apply to Model Fs, but the foam layer is a possible cause for concern as it can invariably degrade with age. However, foam degradation typically doesn't result in a major technical fault with the typical side effect being that keys are more prone to rotating in their place. It only really becomes a significant issue if one opens up the assembly and allows the old foam to uncompress. Replacing the foam layer in a Model F is a documented procedure on deskthority.
Model Fs are known for their high-quality unique-mount PBT dye-sublimated keycaps. Versus the most common keycap material, ABS, PBT is more durable, does not degrade/yellow with age, UV or heat exposure, and will keep its texture for longer without shining. Dye-sublimation is also a very durable text printing method that sinks dye material into the keycap's plastic itself, meaning there is nothing to quickly wear off as would be the case with pad-printing or silk screening. This means many vintage Model F keycaps will still be in good condition, requiring at most a good cleaning.
Model F keycaps are uni-profile, meaning a given keycap can be swapped with another provided they are of the same unit size. This allows every Model F to have innate layout customisability without the user needing to worry about mismatches in keycap sculpting - sculpture is instead provided by the curved internal keyboard assembly. Furthermore, some Model Fs such as the 104-key and 122-key terminal keyboards have two-piece keycaps that allow the user to swap around their layout around without needing to completely dismount the entire keycap. The two pieces are known as the stem (the part that always stays in the barrel) and the keytop (the part that can be easily swapped). That said, most Model F variants that are easily accessible these days lack these. Model F and (buckling spring) Model M keycaps are fully interchangeable granted the correct unit size, thus Model F keycaps can be replaced with Model M keycaps including Unicomp keycaps. Today, Unicomp offers keycaps in a variety of colours and as blanks or with dye-sublimated legends on their website. They can be bought individually or as part of the many predefined sets they offer.
More information: Keyboard Rear Labels topic
The IBM System/23 Datamaster was the first bearer of a Model F keyboard assembly and a buckling spring keyboard at large. The system could come in two versions; IBM 5322 "desktop" and 5324 "floortop". The 5322 was essentially a monocoque with the keyboard integrated into the computer's chassis and case, but the 5324 had a discrete keyboard although both are mechanically identical. The Datamasters were released in July 1981, one month ahead of the more famous IBM Personal Computer that reused the same keyboard assembly (albeit with a different controller board) and thus started the Model F/XT lineage. This keyboard's physical layout was based on the earlier Model B IBM 5251 and 5252 keyboards and would go on to be adapted for various other early Model F keyboards. Both keyboards are noted for their large bezels.
The IBM Personal Computer Keyboard is the most common and widely considered to be the definitive Model F keyboard. It debuted with the original IBM PC (5150) in August 1981 and was reused with the IBM PC/XT (5160) whose name inspired its modern common nickname - F/XT. The F/XT played an important role in establishing the PC as a high-quality computer and solidifying buckling spring-based keyboards as IBM's go-to for well over a decade after its release. Relative to the competition, the F/XT brought unsurpassed reliability and build quality to the mix but arguably suffered from a layout too different from others. Most notably, the F/XT along with its predecessor and successors are criticised for their use of stepped multi-unit keys to reduce the need for stabilisers outside of the spacebar.
The IBM Electronic Typewriter models 65, 85 and 95 were briefly available as IBM's Selectric successor using capacitive buckling spring keyboard assemblies. Introduced in 1982, they're essentially an intermediary step between the aforementioned Selectric typewriter family and Model M-based Actionwriter/Wheelwriter/Quietwriter family but are far less common than both. They replaced the Selectric's notable whiffletree mechanism with a low-power computer that drives the "golfball" print head with solenoids instead. They are also amongst the smallest Model Fs made and use plastic rivets to hold their keyboard assembly together much like their Model M successors.
The IBM Instruments Computer System 9000 Keyboard (P/N 4780898) is a variant of the Model F/XT introduced in May 1982 for use with the titular IBM CS/9000 laboratory computer. It's mechanically identical to the IBM PC Keyboard but lacks flip-out riser feet, traded the square IBM badge for a rectangular one reading "IBM System 9000", and its cable now sprouts out from the left side of the keyboard instead of the back. Due to IBM's repositioning of the CS/9000 as a family of computers in 1984 (the CS/9000 proper was also renamed System 9001), this keyboard later became known as the Standard Keyboard due to the availability of the System 9002's Hybrid Keyboard.
The IBM 6580 Displaywriter Type B Keyboard was a low-profile replacement for the 6580's original Model B based keyboard (that IBM retroactively designated Type A). It was made available for the 6580 dedicated word process sometime in 1982. The Type B keyboard features the same functional layout as the Type A keyboard. In a way, the keyboard's alphanumeric section provides an early glimpse into what would become the ISO layout with 1985's IBM Enhanced Keyboard, making the Type B one of the most modern-looking early Model F keyboards.
The IBM 5291/5292 Display Station Keyboard was the earliest terminal Model F keyboard in production, resembling the IBM 5324 Floortop Keyboard and indeed using the same internal keyboard assembly as the Model F/XT. However, it lacked a controller that could generate scancodes making the keyboard essentially 'brainless' on its own. Its most common host, the 5291 itself, was a low-cost successor to the IBM 5251 Display Station, hence this so-called "bigfoot" Model F also takes on the 5251 keyboard's functional layout. The 5292 is within the same family but adds 7-colour support to the display. Compared to its stylistically similar 5324 counterpart, the 5291/5292 keyboard is slightly smaller but features the three-setting riser feet this keyboard is known for and are presently the larger known IBM keyboard feet.
The 50-key IBM 4704 Display Station Model 100 was the first and smallest keyboard for the IBM 4700 Finance Communication System's 4704 Display Station, introduced in October 1982. It's the second smallest known Model F assembly behind the Model F-based IBM Electronic Typewriter models 65, 85 and 95. It's a matrix-style keypad with three key segments, usually featuring 45 transparent keys and 5 hard-set function keys. The Model 100 acted as a sort of macro pad for the system by allowing the user to map functions to those 45 transparent keys and put custom labels underneath them. It's colloquially referred to as the "F50".
The 62-key IBM 4704 Display Station Model 200 is the smallest alphanumeric keyboard for the IBM 4700 Finance Communication System's 4704 Display Station, introduced in December 1982 alongside the 77-key Model 300. The Model 200 was intended to be the most basic full input device for the 4704, providing only limited user-assigned functions. Nicknamed "Kishsaver" after kishy.ca who introduced them to the modern keyboard community, these have become very desirable due to it being an example of an early 60%-layout keyboard. Starting in 2016, Model F Labs has developed and marketed a modernised recreation of the Model 200 designated as "F62".
The 77-key IBM 4704 Display Station Model 300 is an intermediate-sized alphanumeric keyboard for the IBM 4700 Finance Communication System's 4704 Display Station, introduced in December 1982 alongside the 62-key Model 200. The Model 300 is essentially the same as the Model 200 but comes with an additional 15-key transparent-capped keypad on the right-hand side of the keyboard for user-assigned functions. Starting in 2016, Model F Labs has developed and marketed a modernised recreation of the Model 300 designated as "F77".
The 107-key IBM 4704 Display Station Model 400 is the largest keyboard for the IBM 4700 Finance Communication System's 4704 Display Station, introduced in December 1983 with the IBM 4704-2. The Model 400 features an additional 30-key transparent-capped keypad on top of the Model 300's 77-key design, making it the most versatile and capable keyboard for the 4704 series. It also has an Alps-made counterpart for the Far Eastern markets.
The so-called "blue switch" Model F terminal keyboards were a series of keyboards originally for the IBM 3178 Display Station released in Q1 1983 and later for the IBM 3104 Display Terminal. Characterised by their blue switch used for toggling the terminal's display between mixed-case or uppercase-only characters, these Model Fs featured a layout based on the Model B era IBM 3101, 3275 and 3277 keyboards with two or three function banks depending on SKU. These keyboards are known for sporting a solenoid, something relatively unusual for Model F keyboards. The 3178 keyboards exist in four variants designated C1 to C4; 75-key C1 Data Entry Keyboard, and 87-key C2 Data Typewriter Keyboard, C3 EBCDIC Typewriter Keyboard and C4 EBCDIC Typewriter Keyboard.
The IBM 3101 ASCII Display Terminal
Keyboard was a low-profile replacement for the original Model B-based IBM 3101 keyboard. It's based on the IBM 3104/3178 keyboard design but lacking their characterisitic blue switch, giving these their nickname "blue switchless" Model F. They retain the same physical layout and even have the same solenoid, but they're instead known for having a four 8-switch dip-switch banks underneath a large door on the keyboard's top case piece.
The 104-key Model F terminal keyboard was the first in a long line of so-called IBM "function key keyboards" with a distinct 24-key function key bank, beating the larger and more common 122-key version to market by several months. This 104-key version was made available for the IBM 3290 Information Panel and later IBM 5080 Graphics System. It comes with both an XT-style 10-key function bank to the left of the alphanumeric block and the aforementioned 24-key function key block with "PFxx" legends above the alphanumeric block. Its nickname "unsaver" describes the oxymoronic nature of this being a space-efficient version of an even-larger keyboard despite the fact these are still as large as some modern full-size keyboards. These also feature two-setting riser feet and their ISO-like layout likely played a role in cementing its usage with the later Model M keyboards.
The two IBM 3290-1 keypads were 25-key peripherals for the IBM 3290 Information Panel designed to be used in tandem with "unsaver" 104-key Model F terminal keyboards. Coming in numeric keypad (P/N 6018100) and program function (P/N 6018109) keypad flavours, these are the smallest known Model F assemblies.
The 122-key Model F terminal keyboard was an expanded and far more common version of the tenkeyless "unsaver" 104-key function key keyboard. The primary difference is the addition of an 18-key numeric keypad but stylistically the keyboards look clearly related. These keyboards were made available for various terminals and terminal emulator PCs such as the IBM 3179 Color Display Station, 3180 Display Station, 3205 Color Display Console and 3270 PC. It comes with both an XT-style 10-key function bank to the left of the alphanumeric block and a 24-key "Cmdxx" or "PFxx" function key block above the alphanumeric block. These too feature two-setting feet like the unsaver and are commonly referred to as the "F122" although a 124-key Japanese/Katakana version of the keyboard for the IBM 3205 also existed.
The IBM System 9002 Hybrid Keyboard was a Model F/XT-based keyboard designed for the IBM CS/9000. It served as a counterpart to the original System 9000 Family Standard Keyboard that integrated a similar keyboard assembly with a 57-key functional membrane touch panel, replacing the dedicated touch panel found on previous IBM System 9000 family computers. The name "Hybrid" refers to the use of both capacitive buckling spring key-switches and a membrane touch panel for the keys, which contrasts the Standard Keyboard which was simply a rebadged IBM PC Keyboard with minor modifications. The housing for the keyboard is likely a variation of the IBM 104-key terminal keyboard's case, meaning this is in fact also a hybrid of two Model F keyboard designs. It is very likely the Hybrid Keyboard is the rarest Model F presently known.
The IBM Portable Computer Keyboard was a rehoused Model F/XT made for IBM's first luggable PC - the IBM 5155. Due to its intended use for a portable PC system, the design was lightened by using an all-plastic case and an aluminium keyboard assembly backplate instead of a steel one. The keyboard is also intended to fold up on the front of the host 5155, so there are now two mechanisms on the bottom of the keyboard used for releasing the keyboard so that it can fold down and for detaching the keyboard completely. The keyboard retains a form of riser-style feet, but handles used to fold them down now serve as hinges when the keyboard is coupled to its host and now are also spring-loaded to allow them to be the release mechanism for decoupling the keyboard entirely.
The IBM Personal Computer AT Keyboard was the successor to the Model F/XT as IBM's main PC keyboard and is the last wholly unique Model F design and capacitive buckling springs host introduced. What's now commonly referred to as the "Model F/AT" represented a big step towards the now-standard PC keyboard design with its introduction of the ANSI-style large left shift key, separated numeric keypad and LED lock-lights to the IBM keyboard family. However, it would be quickly supplanted by Model Ms with the Enhanced layout. As the name implies, the F/AT uses the "AT" protocol (IBM scancode set 2) like later PS/2 keyboards. This meant that until the 2010s, F/ATs were considered the most valuable Model F keyboards as were amongst the few Model F variants easily adaptable to modern systems.
The IBM 4980 Display Station Keyboard is a unique version of the 122-key terminal keyboard with 127 keys designed specifically for use and only natively compatible with an IBM 4980 Display Station for IBM Series/1 minicomputers. The extra keys seem to make the keyboard's layout more in line with older IBM Series/1 terminals that sported Model B keyboards. Like a standard 122-key Model F, it comes with both an XT-style 10-key function bank to the left of the alphanumeric block and a 24-key "PFxx" function key block above the alphanumeric block. These too feature two-setting feet and are commonly referred to as either a variant of "F122" or simply "F127".
The IBM EMR and TPC I Keyboards were late variants of the Model F/XT featuring different cables and shielding around the internal logic board. These keyboards were designed to be compliant with the shielding specification of codename TEMPEST, a NATO-recognised U.S. National Security Agency specification regarding protecting against spying with electronic equipment. In particular, these keyboards were designed to not radiate electromagnetic emanations to counter Van Eck phreaking. IBM referred to them as 'TEMPESTed' keyboards. The host systems for the EMR Keyboards are unclear, however, the IBM TPC Keyboard I was designed for the IBM 4450 TPC I, a TEMPESTed version of the IBM 5150 PC. EMR "one" Keyboard features a shielded 5-pin DIN plug, however, EMR II Keyboard and IBM TPC Keyboard I have a DE-9 plug. Known part numbers are limited and only US English TEMPESTed Model F keyboards have been found. P/Ns 100A535 and 100A536 are EMR II Keyboards and P/N 4003444 is the TPC I Keyboard.
The IBM TPC Keyboard III was a TEMPESTed version of the 122-key Model F. The IBM 4456 TPC III was a TEMPESTed version of the IBM 5271 (3270 PC). Like other TPC keyboards, the TPC Keyboard III has a DE-9 plug and was designed to be compliant with the shielding specification of codename TEMPEST, a NATO-recognised U.S. National Security Agency specification regarding protecting against spying with electronic equipment. Interestingly, the TPC Keyboard III has an ANSI-style left shift and 1-unit backspace like a PC/AT layout keyboard. The only known part number is 1385072.
The IBM TPC Keyboard IV was a TEMPESTed version of the Model F/AT. The IBM 4459 TPC IV was a TEMPESTed version of the IBM 5170 PC/AT. Like other TPC keyboards, the TPC Keyboard IV has a DE-9 plug and was designed to be compliant with the shielding specification of codename TEMPEST, a NATO-recognised U.S. National Security Agency specification regarding protecting against spying with electronic equipment. The only known part number is 4010504.
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