Model M Enhanced Keyboard

Also applies to IBM Basic Keyboard, IBM Soft Touch Keyboard, Lexmark Classic Touch Keyboard, Unicomp Customizer, Unicomp Classic & General Electric Healthcare/Marquette Keyboard

IBM Enhanced Keyboard
IBM Enhanced Keyboard[1][1]
clickykeyboards.com - File:252309 10151033065251203 1606697737 n.jpg [accessed 2021-08-02].

The IBM Enhanced Keyboard was IBM's premier keyboard design from the mid-1980s to the mid-1990s. With its distinct style, use of clicky buckling spring key-switches, and far-influencing layout, the Enhanced Keyboard is quite possibly the most famous keyboard of all time and continues to be loved and enjoyed by many. With its many variants for different PCs and terminals and alternate/later branding as the Lexmark Classic and Unicomp Customizer/Classic, the Enhanced Keyboard is also a diverse family of keyboards in its own right.

The Enhanced Keyboard is a member of the Model M keyboard family and is considered to be the definitive member. Model M keyboards were considered to be IBM's flagship keyboards for whatever market the keyboard was intended for, and in that light, the Enhanced Keyboard was IBM's flagship keyboard in the home and office PC, industrial PC and terminal markets during their hey-day. As such, the Enhanced Keyboard enjoys many famous part numbers such as 1388032 (7531 Industrial), 1386303 (3161 terminal), 1390120 (PC/XT), 1390131 (PC/AT), 1391401 (PS/2) and 1392595 (3151 terminal). Including the regional variants, at least 330 part numbers of Enhanced Keyboard exist.

Contents

Summary

Marketing name(s) IBM Enhanced Keyboard
IBM Basic Keyboard
IBM Soft Touch Keyboard
Lexmark Classic
Unicomp Customizer
Unicomp Classic
Designation M
Family Model M
OEM(s) IBM
Lexmark
Maxi Switch
Unicomp
First appeared 21st May 1985 (IBM 7531/7532 announced)[2][2]
IBM - IBM 7531 Industrial Computer Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
[3][3]
IBM - IBM 7532 Industrial Computer Brief Description of Announcement, Charges, and Availability (#185-054) [accessed 2023-10-31].
Switches IBM buckling spring (membrane variant) (most)
IBM Quiet Touch rubber dome (eg, 71Gxxxx)
Keycaps Dye-sublimated (pearl, most) or pad-printed (black, few) PBT
Case dimensions 48.7cm x 20.7cm x 4.7cm (19.17" x 8.15" x 1.85")
Case material PVC (most)
PC+ABS (Unicomp-made since approx mid 2000s)
Case colour(s) Pearl white
Industrial grey
Ambra 'blue-grey'
Raven black
Case screws 7/32" (~5.5mm) hexagonal
Weight 1.67kg (~3.6lbs) to 2.5kg (~5.5lbs) (depending on generation)
Layout 101-104 (ANSI) or 102-105 (ISO) key full-size
Connectivity Modular SDL: XT/AT autosense or AT only to 5-pin 180° DIN or 6-pin Mini-DIN
Fixed cable: AT only to 5-pin 180° DIN or 6-pin Mini-DIN (PS/2), terminal 5-pin 240° DIN or modular 8P5C jack, USB Type-A
Production period 1985 to current
Predecessor(s) IBM 5170 Personal Computer AT Keyboard
Successor(s) IBM/Lenovo Enhanced Performance Keyboard (for IBM)
Unicomp New Model M (for Unicomp)

History

The Enhanced Keyboard was the first discrete (as in, not physically integrated into something) keyboard of the Model M family, only preceded by typewriter keyboard assemblies used on the IBM Wheelwriters 3 and 5 and Quietwriter 7 in late 1984 as the first vessels to bear the membrane variant of IBM buckling spring key-switches. The first system to adopt the Enhanced Keyboard was the IBM 7531 Industrial Computer that was announced in May 1985[2][2]
IBM - IBM 7531 Industrial Computer Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
, a system known for using keyboard P/Ns 1388032 (US ANSI variant) and P/N 1388076 (UK ISO). This was quickly followed by June 1985's IBM 3161 ASCII Display Station with keyboard P/N 1386303[4][4]
IBM - IBM 3161 and IBM 3163 ASCII Display Stations Models 11 and 12 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
.

The Enhanced Keyboard was made available for the wider office and home sectors in April 1986, firstly being introduced with the IBM 5170 PC/AT model 339 at the start of the month[6][6]
IBM - IBM Personal Computer AT 5170 Models 319 and 339 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-22].
, then made available as an option for S-models of the IBM PC/XT, and IBM PC/AT Extended by the end of the month[7][7]
IBM - IBM Enhanced Keyboard for the Personal Computer Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
. The first new non-industrial PC system to ship with a PC-compatible Enhanced Keyboard was the IBM 5162 Personal Computer XT 286 announced September 1986[8][8]
IBM - IBM Personal Computer XT Model 286 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
. Enhanced Keyboards P/N 1390120, P/N 1390131 and regional derivatives of both with similar part numbers are associated with the first home and office Enhanced Keyboards. During this time, IBM also made the Enhanced Keyboard available for its first commercial RISC-based computer, the IBM RT PC[9][9]
Wikipedia - IBM RT PC [accessed 2022-02-19].
, namely P/N 1392366. The Enhanced Keyboard got its big break in April 1987 when IBM released the Personal System/2 series of PCs[10][10]
IBM - IBM Personal System/2 Model 60 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
.

PS/2 Enhanced Keyboards constitute the Model M's most famous variants with part numbers like 13914xx becoming the de facto Model Ms in the eyes of many. Whilst the legacy of IBM PS/2 systems is mixed, the PS/2 Enhanced Keyboard went on to become one of the most famous and revered keyboards of all time and the PS/2 keyboard (and mouse) port also become industry standard. By June 1987, another major Enhanced Keyboard variant was released for the IBM 3151 ASCII Display Station, P/N 1392595[11][11]
IBM - IBM 3151 ASCII Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
. 1989 also saw the launch of the IBM InfoWindow series of Display Stations, starting with the IBM 3471 that sported the common P/N 1394204 (FRU 1394802)[12][12]
IBM - IBM InfoWindow 3471 Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-30].
and would become the most common terminals with Enhanced Keyboards. In June 1991, the Enhanced Keyboard was made available as an option through IBM's Select-A-Keyboard (sometimes written as "Selecta Keyboard") scheme that allowed customers to choose from a variety of keyboards for their system at the time of purchase for no additional charge. At the time, options included the Enhanced Keyboard, the Space Saving Keyboard, and the Host Connected Keyboard[13][13]
IBM - Personal Systems Technical Solutions Issue 4, 1991 (#G325-5013-00) [accessed 2022-08-20].
.

The start of the 1990s saw the formation and sale of IBM Information Products Corporation in August 1990 and March 1991 respectively to facilitate the divesture of IBM’s Lexington, KT and Boulder, CO typewriter and keyboard manufacturing operations[14][14]
Los Angeles Times - IBM Planning to Set Up New Subsidiary : Industry: A buyout firm will be the majority owner of its typewriter and keyboard operations [accessed 2021-09-01].
. This resulted in the formation of Lexmark International, which IBM subsequently started marketing its products with IBM branding (including Enhanced Keyboards) for the next five years[15][15]
IBM - Archives: 1990s - 1991 [accessed 2021-06-17].
. Pretty much all US English Enhanced Keyboard production fell to Lexmark, although IBM US produced occasional examples as late as 1994[16][16]
dustyshed - P/N 1397735 (1994, IBM-US) [accessed 2022-01-23]. License/note: saved from volatile eBay listing.
. IBM Mexico also produced some P/N 1391401 keyboards during this time alongside their usual workload of producing South American models. IBM UK largely continued producing Europe, the Middle East and Africa (EMEA) models by themselves. During the Lexmark era, several new part numbers derived from 1391401 were introduced such as P/Ns 52G7980, 52G9658 (RS/6000 US ANSI but destined for Korean markets[17][17]
IBM - IBM RS/6000 7043 43P Series Service Guide [accessed 2022-01-23].
), 52G9700, 60G3571 (IBM Easy OPTIONS[18][18]
SharktasticA - P/N 60G3571 (1994, Lexmark) [accessed 2022-01-23]. License/note: saved from volatile eBay listing.
), 82G2383 (RS/6000 US ANSI but destined for Chinese markets[17][17]
IBM - IBM RS/6000 7043 43P Series Service Guide [accessed 2022-01-23].
) and 92G7453 (OPTIONS by IBM[19][19]
IBM - Options by IBM: Overview [accessed 2022-01-23].
). Lexmark also introduced their own branded version of the Enhanced Keyboard such as P/N 1398601, which they branded invariably as the Lexmark Classic Touch Keyboard or simply Lexmark Enhanced 101-key Keyboard. Lexmark started selling their own-branded keyboards on 1st April 1992[20][20]
PC Mag - 1993-07 [accessed 2022-01-23].
.

Lexmark and IBM expanded the Enhanced Keyboard's reach to other companies as well. Lexmark made versions for the Enhanced Keyboard for CompuAdd (P/Ns 1369167 and 1397771), Cube Computer Corporation (P/N 1378207), Dell (P/Ns 1397651 and 1369050), GTSI (P/N 70G8638) and Reply (P/N 1395100). By 2nd August 1993, IBM created Ambra Computer Corporation as a wholly-owned subsidiary to market low-cost PCs[22][22]
InfoWorld - 1993-08-02 [accessed 2022-01-23].
and shipped some of these systems with reskinned Enhanced Keyboards largely made by IBM UK. IBM UK's Ambra keyboards were available in two series; AMB100x and AMB200x. AMB100x are coloured blue-grey, have keycaps with Apple-style bottom-left aligned italicised legends and have a unique lock-light overlay with circular view-holes. AMB200x is a more conservative version that simply has a different oval badge and circular view-hole overlay - their case colour and keycaps are identical to standard Enhanced Keyboards. Lexmark additionally produced an Ambra keyboard for the US market that had an isosceles trapezium-shaped logo but otherwise was a standard Enhanced Keyboard (P/N 1378160). By October 1993, IBM introduced what is technically the most unique Enhanced Keyboard variant in the form of a Quiet Touch rubber dome model called the IBM Basic Keyboard (P/N 71Gxxxx). The IBM Basic Keyboard was solely produced by Lexmark (IBM themselves seemingly never continued production after April 1996) and was available as an option for the IBM ValuePoint workstations for AS/400 midrange computers[23][23]
IBM - IBM VALUEPOINT FOR AS/400 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-21].
and later IBM PC 300[24][24]
IBM - IBM PC 300 Series Pentium Systems Announcement Letter [accessed 2022-01-21].
and 700[25][25]
IBM - IBM PC 700 Series -- Pentium/ISA Systems Announcement Letter [accessed 2022-01-21].
series computers.

At some point in 1995, Lexmark and IBM UK introduced their final revision of the Enhanced Keyboard design. P/N 42H1292 for the US market (EMEA/SA versions retained their P/N 13914xx nomenclature) represented the largest change in the keyboard's design by changing the cable position and introducing a new type of pressure-fit controller around the lock-light area. The new controller importantly reduces the part count over the previous Triomate-style controller, however, the position of the lock-lights was changed from bottom-left to roughly middle. Despite this, some keyboards based on the older designs were still produced in 1995 and 1996. By April 1996, Lexmark exited the keyboard market after its five-year contract with its former parent company was over[26][26]
Plastic News - Lexmark exits keyboards, targets printers: firm to outsource more molding [accessed 2022-01-23].
. As such, IBM UK took on the immediate mantle of producing Enhanced Keyboards based on the 42H1292 design and continued producing Model Ms in-house until the end of 1999.

However, 1996 saw former Lexmark (and by extension, IBM) employees form Unicomp, Inc. who purchased IP and tooling from Lexmark to restart Lexington-based keyboard production. Whilst Unicomp could produce some keyboards based on the pre-42H1292 design during its opening years, their products are largely based on 42H1292. By late 1998, Unicomp had established its online presence and was marketing the Enhanced Keyboard as the Unicomp Customizer[27][27]
Unicomp - Unicomp's Customizer Keyboard [accessed 2022-01-21].
. The first major change to the keyboard design was the addition of Windows (super) keys by October 2000, allowing for 104 (ANSI) and 105 (ISO) key layouts[28][28]
Unicomp - The Customizer Keyboard [accessed 2022-01-21].
. In 2006, Unicomp made a USB version of the keyboard. In early 2012, Unicomp renamed the Customizer to Classic[29][29]
Unicomp - Classic [accessed 2022-01-21].
, beginning the present period in the Enhanced Keyboard history.

Whilst the keyboard continues to see production as of 2022, time has certainly taken its toll on the moulds and, unfortunately, production defects are becoming ever increasingly more common. As such, since 2021, Unicomp discontinued most SKUs of the Classic to preserve the life of the moulds as much as possible and advises customers to purchase the Unicomp New Model M instead. Unicomp has recently started the process of retooling, but it's presently unclear if they will introduce entirely new moulds for the Classic. For now, the Classic still endures and Unicomp has made a business for itself making these keyboards for other companies in much the same way as Lexmark in the first half of the 1990s. In particular, Unicomp has produced General Electric Marquette and Healthcare branded keyboards since 2000 and continues to do so as of 2020[31][31]
u/funkmon - I typed on the new Unicomp SSK. *Write-up of visit to Unicomp* [accessed 2022-02-20].
.

Pricing

All inflation adjustments were made with US Inflation Calculator.

Date Model Original price 2022 price
1985-06-18 IBM 3161 terminal, P/N 1386303 $180 USD[4][4]
IBM - IBM 3161 and IBM 3163 ASCII Display Stations Models 11 and 12 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
~$490 USD
1986-02-07 IBM 3164 terminal, P/N 1386304 $200 USD[32][32]
IBM - IBM 3164 ASCII Color Display Station Models 11 and 12 IBM 3161/3163 Feature Cartridges Brief Description of Announcement, Charges, and Availability [accessed 2022-01-30].
~$534 USD
1986-06-16 IBM 3191 terminal, P/N 1390123 $295 USD[33][33]
IBM - IBM 3191 Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-30].
~$788 USD
1987-06-16 IBM 3151 terminal, P/N 1392595 $150 USD[11][11]
IBM - IBM 3151 ASCII Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
~$386 USD
1989-06-20 IBM 3471 terminal, P/N 1394204 $295 USD[12][12]
IBM - IBM InfoWindow 3471 Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-30].
~$696 USD
1992-02-25 IBM PS/2, likely P/N 1391401 $217 USD[21][21]
PC Mag - 25 Feb 1992 [accessed 2022-01-22].
~$453 USD
2000-01-15 Unicomp PS/2 $79 USD[34][34]
Unicomp - Pricing [accessed 2000-01-15].
~$134 USD
2022-01-01 Unicomp PS/2, P/N UNI0416 $104 USD[35][35]
Unicomp - Classic 101 White Buckling Spring PS2 [accessed 2022-01-22].
$104 USD

Design

More information: Model M keyboards

Key-switches

More information: IBM buckling spring#Membrane

Animation of a buckling spring
Animation of a buckling spring[36][36]
Shaddim - File:Bucklingspring-animation-300ms.gif [accessed 2021-09-09]. License/note: CC-BY-2.0.

The most famous feature of the Enhanced Keyboard is its employment of IBM's buckling spring over membrane clicky key-switch design. Such a switch is comprised of a coil spring, rocker (also known as a flipper or hammer) and the membrane circuitry underneath - pressing down on a buckling spring key causes the coil spring to compress and eventually buckle, which then rocks the flipper attached to the bottom of the spring thus actuating the membrane[37][37]
IBM - Rocking switch actuator for a low force membrane contact switch [accessed 2021-06-17].
. The mechanism rocks the membrane before its fully buckled (bottomed out), allowing for part-way actuation. Key-travel is 3.8mm[38][38]
Unicomp - The Customizer Keyboard [accessed 2022-10-04].
.

By 1993, a rubber dome version of the Enhanced Keyboard appeared for those wanting the same keyboard layout, style and construction but quieter. These were marketed as a Quiet Touch version of the Enhanced Keyboard (although named as the IBM Basic Keyboard) and can typically be identified by their part number nomenclature of 71Gxxxx. Quiet Touch keyboards also do not possess part-way actuation and their keycaps are not compatible with buckling spring keyboards. Their key-travel is also reduced to 3mm. Unicomp still offers rubber dome versions of its keyboards and still refers to them as Quiet Touch keyboards. Another more conservative take on a quieter version of the Enhanced Keyboard is the Soft Touch version, which features greased springs designed to suppress spring ping.

Outer case

The Enhanced Keyboard can be easily identified by its unique physical design. Most notably, the keyboard case has a distinct wedge shape seldom copied correctly by other manufacturers and they have a large space above the F-keys where the keyboard's branding typically resides. The keyboard's inner assembly is curved and partially swoops up above the F-keys and the case is designed to accommodate this, allowing for the space above it to hold items such as pens or pencils. Enhanced Keyboards typically use 7/32" (~5.5mm) flanged hex-head screws to hold the top and bottom case pieces together.

The case is typically made from PVC (especially during the IBM years) and such cases do not yellow with UV exposure, however, some Enhanced Keyboards have been known to yellow (especially early IBM UK and later Unicomp variants). It's presently unknown what material early IBM UK keyboard cases that yellowed used, but Unicomp is known to use a PC + ABS blend for their modern cases.

Internal assembly

The aforementioned curved assembly is comprised of four layers; the barrel plate and actuators, the membrane blanket, the membrane assembly, and the backplate.

  1. The barrel plate sits top facing and is used to guide the individual switch components (the buckling spring or Quiet Touch rubber dome actuators) to their correct position above the membrane assembly's contact points. The barrel plate design has a degree of redundancy in the number of barrels available, allowing for a 'one size fit all' design for ANSI and ISO layout keyboards and terminal versions of both. Barrel plates made by IBM UK can be made of Noryl SPN422L (an alloy of PPE, PS and PTFE)[40][40]
    jsheradin - Comment on "Model M Barn find, broken key barrel" [accessed 2022-06-17].
    . On third-generation and later Enhanced Keyboards, the barrel plate is modified with channels to allow for fluid drainage.
  2. The membrane blanket (casually known as a "[rubber] mat") is a rubber or latex sheet used to dampen the stress the actuators exert on the membrane assembly. A Unicomp employee posting on /r/ModelM Discord has stated that a Model M without the blanket is unlikely to reach the rated 25 million key-presses lifetime[41][41]
    troyfletcher#5223 - Discord Message #252446027745853442 on IBM keyboards | /r/ModelM & F [accessed 2023-02-21].
    .
  3. The membrane assembly is a part of the key-switch system used as the circuitry to be actuated and facilitates a 16x8 matrix.
  4. The backplate provides rigidity and the curvature for all the other layers to follow.

The assembly is held together by many plastic rivets designed to provide the tension needed for the buckling springs to operate properly. Unfortunately, these rivets are the single largest flaw in the Model M design as they can weaken and break with age. Such an issue can be permanently solved with a bolt or screw mod.

Keycaps

The keycaps are usually IBM's famed PBT dye-sublimated variety. Versus the most common keycap material, ABS[42][42]
WASD Keyboards - Mechanical Keyboard Guide [accessed 2021-09-09].
, PBT is more durable, does not degrade/yellow with age, UV or heat exposure, and will keep its texture for longer without shining[43][43]
Switch And Click - ABS vs PBT Keycaps: What’s the Difference? [accessed 2021-09-09].
. 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 M keycaps will still be in good condition, requiring at most a good cleaning. Enhanced Keyboard keycaps are also typically two-piece that when present allows you to swap the keytop featuring the text legends instead of having to pull the entire keycap out of the barrel.

Controller

Throughout the years, the Enhanced Keyboard used two main types of controller boards; the Triomate-based membrane dual or triple flex cable connection controller (first through third generation Enhanced Keyboards) and the pressure-based membrane connection "overnumpad" controller (fourth-generation Enhanced Keyboards).

Triomate-based controller

The most familiar Enhanced Keyboard controller PCB is dubbed Triomate-based, named after the type of connector the membrane flex cables use - TE Connectivity's Triomate, pitched 2.54mm. Enhanced Keyboards with this style of controller that also have lock-lights with have their LEDs placed on a separate daughterboard. The number of flex cables could differ:

  1. Very early PC-compatible controllers (~1985-1987) could have two Triomates; 16-pin matrix connection and 8-pin matrix connection. If the host keyboard has lock-lights, the LED daughterboard is hooked up with a 4-pin Berg connector.
  2. Very early terminal-compatible controllers (~1985-1987) could have three Triomates; 16-pin matrix connection, 8-pin matrix connection and 13-pin shorted to PCB GND[44][44]
    Sandy55 - Trivia, Model M & F [accessed 2022-01-31]. License/note: re-use permitted; source should be given.
    .
  3. Most PS/2-compatible controllers (~1987-1991) could have three Triomates; 16-pin matrix connection, 8-pin matrix connection and 4-pin LED lock-lights connection.
  4. Later PS/2-compatible controllers (~1992-1996) could have two Triomates; 16-pin matrix connection and 12-pin combined matrix and LED lock-lights connection.

Aside from the number of Triomate sockets, the next big variance is cabling. Enhanced Keyboards were made with both fixed cables and modular shielded data link (SDL) cables. Terminal Enhanced Keyboards with fixed cables typically had a 2x6 pin cable header whereas PC-compatible Enhanced Keyboards of the 1990s typically had a 4-pin JST header. SDL sockets remained the same throughout the years with only cosmetic/shell colour variance. One thing that didn't change for Triomate-based controllers is power consumption - Model Ms with them can draw between 90 and 130 milliamps depending on the status of the LED lock-lights, which is significantly more than most standard keyboards today[45][45]
Scott W. Vincent - Power Consumption of IBM Model M Keyboards [accessed 2022-02-01].
.

Pressure-based controller

In 1995, the introduction of P/N 42H1292 and its EMEA/SA counterparts saw the move from Triomate-based controllers to a smaller, simpler card that is connected to the membranes' traces by pressure alone. This 25-pin pressure-based controller is sometimes referred to as the "overnumpad controller" due to the fact it's positioned just above the numeric keypad keys. Due to this, the LED lock-lights were placed on the controller itself, eliminating the daughterboard. The LEDs are also placed different compared to the old daughterboard due to the position of the membrane connection pins and the large IC (that the PS/2 version of the controller has), which is what gives fourth-generation Model Ms the characteristic lights that are aligned in the middle of their external overlay instead of bottom left. The change in controller also reduced the part count and power consumption significantly, with Unicomps circa 2001 drawing at most ~30 milliamps with LED lock-lights turned on[45][45]
Scott W. Vincent - Power Consumption of IBM Model M Keyboards [accessed 2022-02-01].
.

The physical size of the overnumpad controller has not significantly changed, although there is some variation in mounting and IC. The main difference over the years is the increase in mounting hole size - Unicomp presently uses 4.3mm mounting holes, however, Lexmark/IBM UK/earlier Unicomp overnumpad controllers had 3.2mm mounting holes[46][46]
purdeaandrei - overnumpad_controller_1xb/README.md [accessed 2022-01-31].
. Additionally, Unicomp has moved to mounting the controller with screws instead of relying on a plastic clip (visible in the photo above, left side of the board right next to the capacitor). In 2006, Unicomp introduced USB versions of its keyboards which required a change in IC (new PS/2 keyboards still used the old larger IC though). In 2020, Unicomp introduced blue LEDs for most of its keyboards. Today, the USB overnumpad controller sports a small Cypress IC and surface-mount components. The Unicomp USB "overnumpad" controller card's codename is "Ruffian", named after a Kentucky racehorse from the 1970s[47][47]
troyfletcher#5223 - Discord Message #1067085568602816572 on IBM keyboards | /r/ModelM & F [accessed 2023-02-22].
.

Possible speaker

Perhaps one of the most common questions people may have about Enhanced Keyboards is the grille on the back of them. This grille is in fact for an internal speaker, but in practice, very few Model Ms populated this and only first to third-generation Enhanced Keyboards have the grille. The speaker was only available on keyboards for IBM workstations of the RT PC and RS/6000 family, and the Soft Touch version of the Enhanced Keyboard (P/N 8184692). The some well known Enhanced Keyboard part numbers are P/N 1392366 (RT PC), 1394540 and 51G8572 (RS/6000). The former has a unique and bulky 6-pin AMP connector on its cable, however, the latter (and the aforementioned Soft Touch Keyboard) use a PS/2 mini-DIN plug with the typically unused pins in the connector used for speaker (since standard keyboard connectivity only requires 4 of the 6 pins on PS/2 mini-DIN).

When present, the device is typically a P/N 1392326 8Ω, 0.2W speaker[49][49]
Ardent Tool - Model M Keyboard [accessed 2022-02-13].
that is exclusively driven by the host computer and was intended to have a frequency response of at least 500 to 5000Hz ± 20dB[50][50]
bitsavers - IBM RISC System/6000, POWERstation & POWERserver Hardware Technical Reference General Information (#SA23-2643-00) [accessed 2023-04-06].
. The speaker was used to provide system audible cues. For RS/6000 keyboards, you would have been required to purchase and fit the IBM Optional Keyboard Cable with Speaker (feature code 6599, FRU 93H8878)[51][51]
IBM - IBM RS/6000 Model 370 Sales Manual [accessed 2022-02-13].
. For fourth-generation Enhanced Keyboards, the speaker grille was removed. However, the artefacts from Lexmark/IBM UK modifying the case moulding to fill in the grille are visually present, even on brand-new Unicomp Classics.

Flip-out feet

All Enhanced Keyboards have single setting flip-out plastic feet. In most cases, they're relatively stubby feet that have a characteristic hollowed-out space in between the two clips that hold the feet in place. However, for some IBM InfoWindow Enhanced Keyboards, an elongated foot variant is known and is likely borrowed from the Type III 122-key Model M design.

Branding

Most Enhanced Keyboards are proudly adorned with the branding of IBM, Lexmark or Unicomp to the point most of the badge styles have become iconic (or infamous) in their own right. These badge styles also prove useful for quickly identifying the approximate period and generation a given keyboard is from. For IBM, the two main styles of badges were a square logo in the top-right corner of the keyboards and an oval logo in the top-left corner of the keyboards.

The black-square logo of early industrial models was technically the first branding Enhanced Keyboards had, however, the silver-square logo first-generation terminal and non-industrial PC-compatible Enhanced Keyboards had is more famous. Square-badge Enhanced Keyboards are typically belonging to the first generation. An oval logo typically means the keyboard is from the second to fourth generations produced between 1987 and 1999. The oval logo has a further three variants; oval with grey text (1987-1992), oval with blue text (1992-1999) and black oval that was used on various industrial Enhanced Keyboards since 1987.

Self-branded Lexmark Classic keyboards featured a rectangle logo in the top-left corner with the Lexmark black and red logo printed on an off-white background matching the rest of the case. Unicomp's self-branded Customizer and Classic keyboards typically feature Unicomp's logo printed on the lock-light overlay or simply lack any branding at all on the top case. Very late keyboards produced by Unicomp for IBM could have the IBM logo printed on the lock-light overlay. Enhanced Keyboards produced by IBM, Lexmark or Unicomp for other companies such as Affirmative, Ambra, Dell or General Electric Healthcare/Marquette could feature a plethora of logo styles in oval, rectangle or lock-light form.

Generations

The Enhanced Keyboard underwent various changes since its inception in 1985, mostly in the name of cost and weight saving required for the keyboard to be a competitive sell in a market increasingly saturated by cheaper PC clones and keyboards in the late 1980s and throughout the entire 1990s. Generally, four distinct generations are recognised by Model M enthusiasts and the following properties are true for IBM UK, IBM US, Lexmark and Unicomp produced Enhanced Keyboards[52][52]
Chyrosran22 - IBM Model M13 Trackpoint II keyboard review (IBM buckling spring) [accessed 2021-09-03].
:

# Year Weight IBM branding Plate Controller style Details
1 1985 2.5kg IBM silver-square 1.2mm, "rainbow" Triomate connectors for membrane, Berg connectors for lock-lights Typically early industrial and terminal, and IBM PC/XT and PC/AT, keyboards
2 1987 2.2kg IBM oval with grey text 1.0mm, grey All triomate connectors Typically PS/2 PC, 3151 terminal, and most industrial keyboards
3 1992 2.06kg IBM oval with blue text 1.0mm, grey All triomate connectors Typically late PS/2 PC and terminals and OPTIONS by IBM keyboards
4 1995 2kg (1.67kg post-1999) IBM oval with blue text, Unicomp logo on lock-lights 0.8mm, grey Pressure-based "overnumpad" Typically OPTIONS by IBM and all Unicomp keyboards

Note

This is a rule of thumb - there may be exceptions. This also doesn't take into account any possible case assembly or controller swapping or outright kitbashing that might result in keyboards made during one generation exhibiting properties of another.

Layout

The eponymous "Enhanced layout" is perhaps the single biggest impact on the computing industry that the Enhanced Keyboard made. The layout can be best described as a fusion of the layouts previously used on the IBM 4704 62/77/107-key Model Fs and IBM 3270 PC 122-key Model Fs, and DEC's LK201 terminal keyboard that was responsible for introducing the inverse-T style cursor keys[53][53]
deskthority wiki - DEC LK201 [accessed 2021-09-04].
. This resulted in a marked difference over the previous IBM PC, PC/XT and PC/AT keyboards, including separated Esc and navigation keys, two new F keys, duplicated Ctrl and Alt keys for ambidextrous access[1][1]
clickykeyboards.com - File:252309 10151033065251203 1606697737 n.jpg [accessed 2021-08-02].
and enlarged backspace key. A change in philosophy was also adopted, with slightly different physical arrangements introduced for US English and rest-of-world versions of the Enhanced Keyboard.

The US English version of the Enhanced layout is now referred to as the ANSI layout (named after the American National Standards Institute) and the European, Middle Eastern and African (EMEA) and South American (SA) versions are now referred to as the ISO layout (named after the International Organization for Standardization). The EMEA/SA keyboard also has many variants within like previous PC keyboards, including versions with different symbol sets for different languages and even different alphabetical key arrangements such as typical QWERTY, QWERTZ (German) and AZERTY (French). ISO keyboards also have an AltGr (Alt Graph) key instead of a right Alt key as another way to access additional and typically uncommon characters for the given host region. A select few EMEA/SA countries such as The Netherlands have [partially] adopted ANSI as their national/preferred layout. Korean and Thai keyboards can also be ANSI-based. Canada (where English and French are co-official languages) has adopted both ANSI (English only) and ISO (Canadian bilingual, aka, English-French/French-Canadian) as possible national layouts.

The Enhanced layout remains the primary layout of computer keyboards, with even Apple adopting a similar physical layout starting with the Apple Extended Keyboard. Minor alterations have been attempted with various levels of success. Most attempts usually end up as a quirk of the manufacturer that tried to introduce it, however, Microsoft's addition of Windows (super) keys supported by the release of Windows 95 resulted in widespread adoption thus most PC keyboards today have them[54][54]
deskthority wiki - Windows key [accessed 2021-09-04].
. Smaller form-factor variants of the Enhanced Keyboard have also materialised such as the tenkeyless layout introduced by the Model M-based IBM Space Saving Keyboard.

Connectivity

The Enhanced Keyboard is best known for using a 6-pin modular AMP shielded data link (SDL) port and a detachable cable. This allowed the keyboard to be uncoupled from its cable as needed. The cable was typically a high-quality grey and thick coiled cable that could stretch as needed, however, black SDL cables are known to exist for early PC/XT and PC/AT Model Ms.

Terminal variants always had fixed cables from the very beginning, however, most later PC Enhanced Keyboards eventually received fixed cables by the mid-1990s that were at first coiled but later straightened.

In terms of protocol, PC-compatible Enhanced Keyboards typically communicated with IBM scancode set 2 (aka, "AT") protocol through an AT (5-pin DIN in 180-degree pin arrangement) or a PS/2 plug (6-pin mini-DIN) on the end of their cables. PC/XT and PC/AT Model Ms could also communicate via IBM scancode set 1 ("XT"), being able to auto-sense what the host computer expects (more info below). Terminal versions spoke IBM scancode set 3 instead, which was either carried via DIN connectors with a 240-degree PIN arrangement or modular 8P5C "RJ-45" jacks.

Auto-sense

Early industrial, and (as aforementioned) PC/XT (eg, P/N 1390120) and PC/AT (P/N 1390131) Enhanced Keyboards, could communicate via all three IBM scancode sets. These keyboards supported a "Mode 1" and "Mode 2" communication that allows for set 1 and set 2 communication respectively. Mode 2 can further be used to access set 3 or go back to set 1. The modes are selected via an auto-sense routine that figures out what the host system wants based on the status of the 'clock' line. This mode selection can only be achieved immediately after the keyboard's power-on reset (POR) and the host system must be compliant otherwise the keyboard will essentially default to Mode 2. The July 1985 IBM 7531/7532 Industrial Computer Technical Reference System Unit describes the procedure:

If the 'clock' line is active (high) immediately after POR, the keyboard sets up for Mode 1 operation. It then waits for the 'clock' line to become inactive (low), executes the basic assurance test (BAT), and returns the completion code.

If the 'clock' line is inactive (low) immediately after POR, the keyboard executes the BAT, waits for the 'clock' line to become active (high), and sends the completion code in Mode 2 protocol. If the system has not made the 'data' line inactive within 40 microseconds, Mode 2 operation is established. If the 'data' line has become inactive within this time, Mode 1 is established.

Mode 1 uses scan code set 1 only. Mode 2 uses scan code set 2, but can be switched to scan code set 1 or scan code set 3 using the Select Alternate Scan Codes command.[55][55]
IBM - IBM 7531/7532 Industrial Computer Technical Reference System Unit (#6523261) [accessed 2022-06-21].

The March 1986 revised IBM Personal Computer XT & Portable Personal Computer Technical Reference mentions the following and gives a table of scancodes for Enhanced Keyboards that appears to be set 1, confirming the procedure applies to them and that the Enhanced Keyboards of the time indeed support set 1.

The keyboard has 101 keys (102 in countries outside the U. s.). At system power-on, the keyboard monitors the signals on the 'clock' and 'data' lines and establishes its line protocol.[56][56]
IBM - IBM Personal Computer XT & Portable Personal Computer Technical Reference [accessed 2022-06-21].

The keyboard sections of earlier technical references like IBM PC 5150 (August 1981) and IBM PC/XT 5160 (April 1983) do not mention of clock becoming high immediately after POR[57][57]
IBM - IBM Personal Computer Technical Reference (#6025008) [accessed 2022-06-21].
[58][58]
IBM - IBM Personal Computer XT Technical Reference (#1502237) [accessed 2022-06-21].
, which means this mode selection is unlikely to work for earlier systems. If an auto-sensing Enhanced Keyboard is hooked up to an incompliant system, it will either not work or produces random characters at best and proves ultimately unreliable[59][59]
voidstar - 5150: Connecting a Keyboard [accessed 2022-01-21].
. It's uncertain if BIOS upgrades were available that specifically addressed this - some have reported these keyboards working on 5150 or earlier 5160s, which might confirm the issue can be addressed without a motherboards swap. The following systems have been said to ship with an Enhanced Keyboard or had an Enhanced Keyboard added later as an option:

It should also be noted that some later PC-compatible Enhanced Keyboards have invariably been said to support mode selection and thus scancode set 1 (and 3), including P/N 1391401 and P/N 52G9658[61][61]
minuszerodegrees.net - IBM 5150 - Keyboards [accessed 2022-06-21].
, when hooked up to a compliant system.

Known variants

Industrial Keyboard (1985)

eg, P/Ns 1388032, 1390653, 1394946, 1394950

The first IBM Enhanced Keyboard to be announced was the IBM Industrial Keyboard with the characteristic "industrial grey" cover set colour. Compared to the later pearl white Enhanced Keyboards, Industrial Keyboards are essentially the same underneath but it's believed the unique colour was intended to help hide the dirt and damage expected to be inflicted upon the keyboard within an industrial environment. The IBM Industrial Keyboard was seen in May 1985 as the keyboard for the IBM 7531 and 7532 Industrial Computers[2][2]
IBM - IBM 7531 Industrial Computer Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
[3][3]
IBM - IBM 7532 Industrial Computer Brief Description of Announcement, Charges, and Availability (#185-054) [accessed 2023-10-31].
. Their announcement came about a month ahead of the first terminal Enhanced Keyboards, meaning these had the honour of introducing the 101-key (ANSI) and 102-key (ISO) style IBM Enhanced layouts. 753x Industrial Keyboards had black-square IBM badges and part number nomenclature of 13880xx. The following year, some examples of silver-square IBM Industrial Keyboards appeared such as P/N 1390653 (known to have black or silver square badges). In 1989 after all the square-badge Industrial Keyboards, IBM introduced a new generation of keyboards with black-oval branding for the IBM 7541, 7542[63][63]
IBM - IBM 7541 Industrial Computer Model 011, IBM 7541 Industrial Computer Model 111 & IBM 7542 Industrial Computer Model 011 Brief Description of Announcement, Charges, and Availability (#ZG89-0142) [accessed 2023-10-31].
, 7561 and 7562[64][64]
IBM - IBM 7561 Industrial Computer Model 011, IBM 7561 Industrial Computer Model 111 & IBM 7562 Industrial Computer Model 011 Brief Description of Announcement, Charges, and Availability (#ZG89-0141) [accessed 2023-10-31].
Industrial Computers and IBM GEARBOX Model 800 series[65][65]
IBM - GEARBOX Model 800 Industrial Computer Brief Description of Announcement, Charges, and Availability (#ZG89-0248) [accessed 2023-10-31].
usually with 13949xx part number nomenclature. From the mid-'90s onwards, these keyboards could also use blue-oval IBM branding when made by Unicomp for IBM. All Enhanced Keyboard-style Industrial Keyboards from IBM were AT compatible but at least 753x keyboards were also capable of XT/AT autosense[56][56]
IBM - IBM Personal Computer XT & Portable Personal Computer Technical Reference [accessed 2022-06-21].
.

DIN terminal Enhanced Keyboard (1985)

eg, P/Ns 1386303, 1386304, 1390123, 1390636, 1390766

The first Enhanced Keyboard available in significant numbers and can be relatively easily sourced today are the terminal Enhanced Keyboards for the IBM 316x family ASCII Display Stations. The IBM 3161 ASCII Display Station Keyboard such as P/N 1386303 came first in June 1985 with the IBM 3164 ASCII Color Display Station Keyboards such as P/N 1386304 dropping in February 1986. Also in 1986, this keyboard design was made available for the IBM 319x family Display Stations as well, resulting in P/Ns 1390123 (IBM 3191), 1390636 (3196) and 1390766 (3192). All such early terminal Enhanced Keyboards were known to sport silver-square IBM badges and featured 240-degree pin arranged DIN plugs much like their 122-key counterparts of the era. In terms of layout, terminal Enhanced Keyboards generally follow the Enhanced layout with only functional differences rather than physical, however, one exception is what would be the upper vertical 2u key on the rightmost column used for numeric keypad "+" is split into two 1u keys on terminal variants. This results in a 102-key ANSI and 103-key ISO layout.

PC/XT Enhanced Keyboard (1986)

eg, P/N 1390120

The PC/XT Enhanced Keyboard was launched at the same time as the PC/AT Enhanced Keyboard in April 1986 and was originally intended to be used with S-model IBM PC/XT systems. Despite this, PC/XT Enhanced Keyboards have the ability to change between IBM scancode set 1 and 2 automatically, however, incompatibilities with the IBM 5150 PC (which uses the same protocol as XT-class computers) have been reported. Later in 1986, the PC/XT Enhanced Keyboard started shipping with the IBM 5162 PC/XT 286. They were also shipped with IBM 5160 PC/XT models 089, 268, and 278[60][60]
IBM - 5160 IBM Personal Computer XT Sales Manual (#ENUS5160) [accessed 2022-06-21].
. Due to its intended use with XT-class computers, these omit lock-lights much like their terminal counterparts. PC/XT Enhanced Keyboards typically have a part number within range of 1390120. PC/XT Enhanced Keyboards were only made to first or second-generation standards and always retained an IBM silver-square badge. PC/XT Enhanced Keyboards originally came with a black SDL cable with a full-size 5-pin DIN connector, but the more common SDL to PS/2 cable could also be used.

PC/AT Enhanced Keyboard (1986)

eg, P/N 1390131

The PC/AT Enhanced Keyboard was launched at the same time as the PC/XT Enhanced Keyboard and was intended to be used with IBM PC/AT Extended systems. Apart from the inclusion of lock-lights, these are essentially the same as the PC/XT Enhanced Keyboard, including having the ability to automatically change between IBM scancode set 1 and 2. PC/XT Enhanced Keyboards typically have a part number within range of 1390131. PC/AT Enhanced Keyboards were only made to first or second-generation standards and always retained an IBM silver-square badge. PC/AT Enhanced Keyboards originally came with a black SDL cable with a full-size 5-pin DIN connector, but a more common SDL to PS/2 cable could also be used.

ALA DIN terminal Enhanced Keyboard (1986)

P/N 1390680

The ALA Keyboard was a version of the DIN plug based terminal Enhanced Keyboard that has numerous diacritics keys to support American Library Association (ALA) character entry. It was intended for IBM 3163 and 3164 ASCII Display Station models 860 and 861, which were specifically designed for supporting these characters for library environments. It was made available in September 1986 and only for US English users[69][69]
IBM - IBM 3162 ASCII Display Station, new non-IBM emulation cartridges, new 3163/3164 ALA models, IBM 3161, 3163, and 3164 functional enhancement cartridges Brief Description of Announcement, Charges, and Availability (#186-167) [accessed 2022-06-14].
.

RT PC & RS/6000 Enhanced Keyboard (1986)

eg, P/Ns 1392366, 1394540, 51G8572

IBM made the Enhanced Keyboard available for its efforts in RISC computing, starting with its first RISC-based commercial computer - the IBM RISC Technology Personal Computer (RT PC). Whilst the RT PC itself wasn't a commercial success[9][9]
Wikipedia - IBM RT PC [accessed 2022-02-19].
, its silver-square badge P/N 1392366 keyboard became the first Enhanced Keyboard to have an internal speaker. IBM's February 1990[70][70]
Wikipedia - IBM RS/6000 [accessed 2022-02-19].
launching IBM RISC System/6000 (RS/6000) family become the largest adopter of Model Ms with speakers. The early and most common RS/6000 Enhanced Keyboards had part numbers in range of 1394540, however, some new Lexmark-era part numbers such as 51G8572 were introduced later on. The early RT PC versions of this keyboard used a unique and bulky 6-pin AMP connector on its cable and weren't completely natively compatible with PS/2 compatible PCs, however, it can be converted with Soarer's Converter. The RS/6000 era versions reverted to PS/2 and can easily be used on PS/2 compatible PCs. On PS/2 plug versions, the speakers are wired to use the typically unused pins on the PS/2 plug, however, no standard PS/2 compatible PC or port is configured to be able to operate these pins and thus the speakers.

PS/2 Enhanced Keyboard (1987)

eg, P/Ns 13914xx, 52G7980, 52G9658, 52G9700, 60G3571, 82G2383, 92G7453

The second and third-generation PS/2 Enhanced Keyboards are the most common and recognisable. The design is an evolution from the PC/AT Enhanced Keyboards, now sporting an oval-shaped badge with grey or blue text depending on generation and a controller PCB that ditched Berg-style connectors for the lock-lights in favour of a membrane flex cable. PS/2 Enhanced Keyboards consistently retained SDL cables until 1993, after which numerous variants produced by Lexmark appeared that invariably dropped SDL for fixed cables whilst not altering the internal design significantly. In 1995, these were succeeded by the fourth-generation design dubbed "Late PS/2 Enhanced Keyboards". Second and third generation PS/2 Enhanced Keyboards commonly have a part number within range of 1391401, although the Lexmark era saw PS/2 Enhanced Keyboards in the 5xxxxxx, 6xxxxxx, 8xxxxxx and 9xxxxxx range introduced.

8P5C terminal Enhanced Keyboard (1987)

eg, P/Ns 1392595, 1393705, 1394204, 1395162, 1395665

The terminal Enhanced Keyboards with 8-pin modular (ie, same style of jack as RJ-45 and ethernet) connectors are the most common terminal Enhanced Keyboards. They inherit the 102/103 key physical layout of its DIN plug predecessors. This style was introduced with the IBM 3151 ASCII Display Station in June 1987[11][11]
IBM - IBM 3151 ASCII Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
with its P/Ns 1392595 (ASCII-style) and later 1395162 (PC-style) keyboards. The keyboard design was also widely adopted by the IBM InfoWindow family of Display Stations first seen in 1989. One interesting thing to note with many of the InfoWindow Enhanced Keyboards is that they could have longer than usual flip-out feet and even a cable router, something reminiscent of the Type III 122-key Model M also introduced in 1989.

PC/3270 Enhanced Keyboard (1987)

P/N 1391580

P/N 1391580 is a version of the standard PS/2 Enhanced Keyboard with unique keycaps for IBM 3270 terminal emulation. They notably sport a combined F1/F13 to F12/F24 function key row, front printing on the numeric keypad, various blue sublegends for PC-specific functions on terminal-layout keys and green Ctrl legends. The earliest examples of these are found in the latter half of 1987[72][72]
ASK Keyboard Collection - SNKB-M1987-EET-101 [accessed 2023-01-30]. License/note: CC-BY-NC-SA 4.0.
, but little to no IBM documentation on these exist including anything indicating an announcement or launch date. At one point, Unicomp sold leftover examples of P/N 1391580 in a warehouse liquidation sale for $84 USD in 2017[73][73]
Unicomp - IBM 1391580 Buckling Spring PS/2 Keyboard - 101 keys with PC/3270 emulation legends [accessed 2023-01-30]. License/note: retrieved via Wayback Machine (2017-05-01 capture).
.

Airline reservation system PS/2 Enhanced Keyboard (1987)

P/N 1393464

P/N 1393464 is a version of the standard PS/2 Enhanced Keyboard with unique keycaps for airline reservation software. This keyboard today is widely associated with Sabre Corporation with various examples of P/N 1393464 with Sabre branding stickers observed. However, they were not the only company to utilise this keyboard. By October 1987, United Airlines (and to a lesser degree Delta Airlines) committed to purchasing a considerable number of IBM PS/2s for their airline reservation systems[75][75]
InfoWorld - 5 October 1987 [accessed 2022-02-20].
and it's believed this keyboard served their systems too.

Dell-branded PS/2 Enhanced Keyboard (1991)

P/Ns 1397651, 1369050

Almost immediately after Lexmark's founding, IBM's then-rival Dell started putting their name to Enhanced Keyboards. P/N 1397651 was the first to appear, which was simply a standard PS/2 Enhanced Keyboard with modular SDL to PS/2 cable. This part number originally featured a rectangle old-style minimalistic Dell logo, although by 1993, they started featuring Dell's more familiar and current logo with a rotated "E". It should be noted that P/N 1397651s with Honeywell branding have also been observed, however, it was theorised that Dell sub-contracted for Honeywell due to the fact the observed example of a Honeywell P/N 1397651 also had a "Dell Field Service" sticker on it[77][77]
Deskthority - HoneyWell Model M "Dell Military Service"? [accessed 2022-02-20].
. P/N 1369050 appeared by 1994 and was a fixed-cabled PS/2 Enhanced Keyboard with the more familiar Dell logo. Other than their branding, these keyboards are unremarkable.

CompuAdd-branded AT Enhanced Keyboard (1993)

P/Ns 1369167, 1397771

CompuAdd, a PC manufacturer from Texas, also put their name to Enhanced Keyboards produced by Lexmark and they appeared not long before their 1994 bankruptcy. CompuAdd Enhanced Keyboards used fixed grey cables with an AT-style full-size 5-pin DIN plug and could come with a standard ISO layout (for example, the Arabic P/N 1369167) or a so-called "Asian 101" layout (the more well-known US English P/N 1397771). The latter layout has a 1-unit backspace and a backwards-L shaped (aka, "big-ass") enter key just like IBM's PC/AT Keyboard layout.

ICPI Ambra PS/2 Enhanced Keyboard (1993)

P/Ns AMB100x, AMB200x, 1378160

Ambra Computer Corporation and its parent ICPI were IBM subsidiaries that marketed low-cost PCs, some of which included third-generation Enhanced Keyboard derivatives. AMB100x (aka, "1-series") and AMB200x ("2-series") are the European versions made by IBM UK, and P/N 1378160 is a singular US ANSI version based by Lexmark. The 1-series featured an all grey-blue cover set (with the top part lighter than the bottom), an oval badge with the Ambra logo inside, bottom-left aligned italicised legends on its keycaps and circular view holes for the LED lock-lights. The 1-series could also invariably come with a permanently attached PS/2 cable or a modular 6-pin SDL to PS/2 cable. The 2-series by contrast is a more conservative take featuring only an oval badge with the Ambra logo inside and circular view holes for the LED lock-lights, otherwise, the case and keycap style are the same as a standard Enhanced Keyboard. P/N 1378160 is simply a standard Enhanced Keyboard with an isosceles trapezium-shaped Ambra logo. All Ambra-branded Enhanced Keyboards have fixed cables.

Quiet Touch PS/2 Enhanced Keyboard (1993)

eg, P/N 71G46xx

The IBM Basic Keyboard was a version of the third-generation PS/2 Enhanced Keyboard with Quiet Touch key-switches. It was likely named "Basic Keyboard" to avoid any potential confusion as the keyboard design from the outside is identical to other fixed-cable third-generation Enhanced Keyboards. The Basic Keyboard retains high component commonality with the Enhanced Keyboard with the only differences being the membrane's actuator (rubber dome instead buckling spring) and the keycap mount. As such, it's technically possible to convert a Basic Keyboard to use buckling springs. Most IBM-branded Basic Keyboards have a part number like 71Gxxxx, which is the easiest way to identify one of these from photos. To this day, Unicomp continues to sell and refer to rubber dome versions of its Model Ms as Quiet Touch or Q/T for short.

Soft Touch RS/6000 Enhanced Keyboard (1994)

P/N 8184692

The IBM Soft Touch Keyboard was a version of the PS/2 compatible RS/6000 Enhanced Keyboard that featured greased buckling springs. The grease is used to make the keyboard queiter by muting the spring's ping (high-pitched resonation after clicking) but doesn't completely mute the keyboard.

Bull-branded RS/6000 Enhanced Keyboard (1995)

P/N 1399240

Groupe Bull is a French computer company that in Q4 1993 started selling rebranded variants of IBM RS/6000 workstations known as the DPX/20 series[81][81]
Tech Monitor - BULL RELEASE SIX NEW DPX/20 VARIANTS OF RS/6000 [accessed 2022-08-02].
. Naturally, Bull contracted Lexmark to produce a version of the IBM RS/6000 Enhanced Keyboard for them. P/N 1399240 is presently the only part number observed thus far and its earliest appearance is 1995. The keyboard is mechanically identical to its IBM counterparts, sporting an internal speaker and SDL connection. The main cosmetic difference is the cylindrically-protruding Bull DPX/20 badge in place of an oval badge and the LED lock-light overlay sticker is noticeably greyer than usual.

Late PS/2 Enhanced Keyboard (1995)

eg, P/N 42H1292, late 13914xx

This represents the final iteration of the Enhanced Keyboard design that involved Lexmark or IBM - the fourth generation. Indeed, these introduced the biggest change to the Enhanced Keyboard design by changing the cable position, blocking off the speaker grille, and introducing a new type of pressure-fit controller around the lock-light area. Now, the (always non-coiled) cable sprouts from the right-hand side of the keyboard. The new controller importantly reduces the part count and power consumption over the previous Triomate-style controllers, however, the position of the lock-lights was changed from bottom-left to roughly middle. This means fourth-generation Enhanced Keyboards can be easily identified by the new lock-light overlay. P/N 42H1292 (the US ANSI model) is most commonly associated with this keyboard; whilst P/N 1391401 (former US ANSI part number) was not carried forward, EMEA/SA models still retained the old 13914xx style part numbers. After IBM UK quit Model M production, Unicomp continued production of late PS/2 IBM Enhanced Keyboards into the early 2000s.

Maquette Keyboard (1998)

The early Maquette Keyboard IBM UK produced for Marquette Medical Systems Inc. in the late 1990s was a [cosmetically speaking] highly customised version of the late PS/2 Enhanced Keyboard. Marquette, based in Milwaukee, Wisconsin, was the United States' largest producer of electrocardiography equipment used to monitor vital signs during the late '90s. They were acquired by General Electric Medical Systems in 1998[83][83]
Los Angeles Times - GE Medical Agrees to Buy Marquette for $808 Million [accessed 2022-12-05].
. These keyboards were produced for their PC-based equipment and thus have various specialised keycaps; the F-keys and numeric keypad legends were entirely replaced with specialised legends and most of the alphanumeric keys have secondary legends. The lock-light overlay was also custom, only exposing the Caps Lock indicator and written across it were phone numbers for support lines. Despite the fact it's a non-IBM product, early Marquette Keyboards used part number 42H1292 just like the standard US ANSI layout fourth-generation PS/2 Enhanced Keyboard. The early Marquette Keyboard was replaced by a Unicomp-made updated keyboard with "GE" branding in 2000.

Unicomp Customizer/Classic (1998)

eg, P/N 42H1292U, UNI041A, UB434HA

The Unicomp Classic (originally called Customizer) is the continuation of fourth-generation Enhanced Keyboard production under Unicomp. At first, the keyboard design and quality remained about the same as its immediate Lexmark and IBM UK predecessors. However, Unicomp soon started altering the design. In October 2000, Unicomp first made Windows keys available as an option[28][28]
Unicomp - The Customizer Keyboard [accessed 2022-01-21].
. In 2006, Unicomp made a USB version of the keyboard available. In July 2013, Unicomp revised its Windows keys layout designs to more closely follow the traditional Enhanced layout, whilst also releasing an entirely new 103 (ANSI) and 104 (ISO) key design that retained the 7u spacebar and filled in the blanks between the Ctrl and Alt keys[84][84]
Unicomp - Unicomp Product News - Revised 104-key Layout [accessed 2022-02-20].
(aka, a Tsangan bottom row design). Quality remained consistent until the late 2000s when time began to take its toll on the keyboard's moulds. Today, Unicomp Classics may have noticeable blemishes and dimples on the exterior, although they are still mechanically sound. In 2020, Unicomp released the New Model M to succeed most of its old product lines and now recommends its customers purchase that keyboard instead. Unicomp has also discontinued many of its Classic SKUs, however, a small selection remains on sale (including the classic pearl white and 101/102 version) for those who still want one.

Galactech SmarTrex POTS Keyboard (1999)

P/N GALII11

Galatech Corporation's SmarTrex Keyboard is a heavily modified Unicomp Customizer with Quiet Touch rubber dome key-switches. The most obvious modification is the telephone cradle and phone jack, which supports a plain old telephone system (POTS) analogue line. It's also unique for being built to almost third-generation Model M standards, featuring a cable spouting from the classic (left-side) position and a Triomate-based controller. They're very uncommon and only examples produced in 1999 have been observed thus far.

Florida Gators & Kentucky Wildcats Keyboards (1999)

P/Ns UNIFLKB, UNIKYKB

From 1999 until the end of the 2000s, Unicomp produced themed versions of the Customizer with Florida Gators college American football and Kentucky Wildcats college basketball team styling. They had various orange and white or blue and white keycaps respectively, as well as a unique squircle-shaped badge in the place where most Enhanced Keyboards have an oval or rectangle-shaped badge. Otherwise, these are fairly standard PS/2 Model Ms of their period.

General Electric Healthcare/Marquette Keyboard (2000)

eg, P/Ns UNZ4416, UNZ3416, 2045802-001, 2045802-002, 2054858-001, 2054858-002, 2054858-003

Unicomp Customizers and Classics produced for General Electric were an updated version of the original early Marquette Keyboard and constitute the seemingly most common, non-IBM/non-Lexmark/non-Unicomp branded Enhanced Keyboard derivative known. Around two years after GE Medical Systems acquired Marquette Medical Systems Inc. in 1998, Unicomp started producing this updated design that added "GE" branding and increasingly more customisations to the keycaps. Whilst the exact list of customisations has indeed changed over the years, the typical Unicomp-made GE Healthcare/Marquette Keyboard's F-keys and numeric keypad legends are entirely replaced with specialised legends, most of the alphanumeric keys have secondary and tertiary legends, the Alt keys are replaced with "Action" keys, the Tab and Enter keys lack their usual symbols, the Tab key is also capitalised, and the numeric keypad largely has bright yellow keycaps. Early GE Model Ms were typically branded GE Marquette to reflect their origin at Marquette, but the latest ones are now branded GE Healthcare. GE Healthcare keyboards could be intended for use with their CardioLab Electrophysiology Recording System, Mac-Lab Hemodynamic Recording System, or both. All known GE Model Ms are PS/2 based and can be used like any other PS/2 keyboard as the customisations are purely cosmetic.

Unicomp Customizer w/ white-on-black keycaps (2003)

P/N UB20416

As early as 2003[89][89]
Brandon @ ClickyKeyboards - 2003 Unicomp black model M (UB20416) Oct 16, 2003 [accessed 2022-02-20].
, Unicomp sold a version of the Customizer with raven black Model M13-style white text on black background (WoB) keycaps, making this the only buckling spring Enhanced Keyboard or derivative that was sold as an entirely black keyboard. The white text was pad printed just like black Model M13s, meaning they're unfortunately perishable with use. The keyboard (along with Unicomp's use of WoB keycaps) came to an end before the end of the decade.

Part number list

280 part numbers have been found in the ASK Keyboard Part Number Database. If you believe a relevant part number is missing, you can help improve this list by requesting a submission for it to be added.

Further reading & resources

Internal

External

Sources

ASK. Admiral Shark's Keyboards original content. License/note: CC BY-NC-SA 4.0.

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  3. IBM - IBM 7532 Industrial Computer Brief Description of Announcement, Charges, and Availability (#185-054) [accessed 2023-10-31].
  4. IBM - IBM 3161 and IBM 3163 ASCII Display Stations Models 11 and 12 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
  5. webwit - Index of /input/ibm_industrial [accessed 2021-12-07]. License/note: public domain.
  6. IBM - IBM Personal Computer AT 5170 Models 319 and 339 Brief Description of Announcement, Charges, and Availability [accessed 2022-01-22].
  7. IBM - IBM Enhanced Keyboard for the Personal Computer Brief Description of Announcement, Charges, and Availability [accessed 2022-01-20].
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Recent updates

2024-01-09 Revisions for Model M Enhanced Keyboard wiki page have been published - Updated photos and info for ICPI Ambra subsection
2023-11-19 Revisions for Model M Enhanced Keyboard wiki page have been published - Moved introduction ahead of Contents, improved Summary, mentioned non-US ANSI possible layouts in Layout, rewrote Industrial Keyboard (1985) & add link to Enhanced Keyboard key-matrix simulator
2023-10-28 Revisions for Model M Enhanced Keyboard wiki page have been published - Fix broken 2020 new-style USB "overnumpad" controller (bottom) image
2023-04-26 Revisions for Model M Enhanced Keyboard wiki page have been published - Updated Ambra AMB2001 photos
2023-04-24 Revisions for Model M Enhanced Keyboard wiki page have been published - Update photos for Unicomp Classic P/N UB434HA
2023-04-19 Revisions for Model M Enhanced Keyboard wiki page have been published - Add part number list section
2023-04-10 Revisions for Model M Enhanced Keyboard wiki page have been published - Rename "Variations" section to "Known variants"
2023-04-06 Revisions for Model M Enhanced Keyboard wiki page have been published - Add info about speaker's frequency response + source
2023-04-06 Revisions for Model M Enhanced Keyboard wiki page have been published - Correct "queues" to "cues"
2023-04-05 Revisions for Model M Enhanced Keyboard wiki page have been published - Added new photos of P/N 1394204