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Model M keyboards

IBM's fifth generation of keyboards

Contents

Background

Various Model M keyboards<a class='source-link' href='/wiki?id=modelm#Sources'><sup>[ASK]</sup></a>
Various Model M keyboards[ASK]

The Model M is a large family of computer keyboards created by IBM and later sustained by Lexmark, Unicomp, and Toshiba TEC. It is IBM's fifth generation of keyboards, following the older but related Model F family. The sole unifying principle of the Model M family is the use of membrane sensing circuits whilst mostly being flagship products in their respective target market segments; whilst membranes are common today, IBM's adoption of it contrasted the capacitive assemblies used by IBM previous two major families of keyboards - the aforementioned Model F and the earlier Model B. Other common well-known features found on Model Ms include membrane buckling spring switches and plastic riveted assemblies, although not all Model Ms featured either, making the family less unified than previous generations.

Today, buckling spring Model Ms are regarded as one of the best families of keyboards created due to their unique auditory and tactile feedback capabilities. Whilst perhaps only bested by IBM's earlier creations in this regard, the majority of Model Ms feature more digestible physical layouts, are typically cheaper to buy and there's a superior availability of spare parts should they be needed. Some consider Model Ms to also be a "gateway drug" into the wider field of vintage and/or IBM keyboards.

History

1984 Hattiesburg American advert showing<br />the first Wheelwriters and Quietwriter<a class='source-link' href='/wiki?id=modelm#Sources'><sup>[2]</sup></a>
1984 Hattiesburg American advert showing
the first Wheelwriters and Quietwriter[2]

The story of the Model M family begins in late 1983 when IBM patented the membrane buckling springs switch design invented by Edwin T. Coleman, III. The intent of the new membrane-driven design was to half the production cost of the buckling springs switch compared to Richard Hunter Harris' 1977 capacitive buckling springs design used in the Model F family keyboards[1]. The first vessels of this switch design were the in fact typewriters; namely the IBM Wheelwriter 3, Wheelwriter 5 and Quietwriter 7, which were all released on 13th December 1984[2].

The first discrete keyboard with this switch design was the IBM Enhanced Keyboard, which was announced in May and June 1985 in the forms of the IBM 7531 Industrial Computer Keyboard (P/N 1388032)[3] and IBM 3161 ASCII Display Station (P/N 1386303)[4] respectively. These was also officially designated "Model M" unlike the earlier Wheelwriter-family keyboard assemblies, and the home and office PC-compatible versions of the Enhanced Keyboard such as P/Ns 1390120 (PC/XT), 1390131 (PC/AT) and 1391401 (PS/2) cemented the reputation of the Model M and the status of the Enhanced Keyboard being the definitive member of the family. At the same time, the family started expanding with a 122-key terminal keyboard, 84/85-key tenkeyless keyboard, and various smaller keypad designs spawning between 1985 and 1987.

The 1990s were very eventful for the Model M family, with the early '90s seeing 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[5] (IBM UK and Mexico still continued their own production). This resulted in the formation of Lexmark International, which IBM subsequently started marketing its products with IBM branding (including Model M keyboards)[6] with a five-year contract to do so. The '90s saw the rise of numbered Model M variants, resulting in M1 through M15 (excluding M10, M12 and M14) being used as designations for unique keyboard designs sequentially from 1990 to 1994. The family also gained numerous members that did not use buckling springs or even full-travel switches, instead using technologies such as Quiet Touch-branded rubber domes (IBM Basic Keyboard) or buckling rubber sleeves (M3, M4/M4-1, M6/M6-1, M7, M8, M9 and M11). Attempts to combine keyboard and pointing devices were also made, with keyboards featuring integrated trackballs (M5-1/M5-2) and TrackPoint isometric pointing sticks (M4-1, M6/M6-1, M13) being released through 1993 and 1994.

Lexmark advert from December 1993<a class='source-link' href='/wiki?id=modelm#Sources'><sup>[7]</sup></a>
Lexmark advert from December 1993[7]

When IBM's five-year contract with Lexmark was reaching its end, keyboard sales accounted for only 5% of Lexmark's gross profit and thus they made the decision in late 1995 to exit the keyboard market by April 1996. Assets related to buckling springs and Quiet Touch Model M keyboard production such as tooling were sold off to both IBM UK and Maxi Switch, with the latter receiving the 1983 membrane buckling springs patent[8]. Also in 1996, a group of former Lexmark (and in some cases former Lexmark and IBM) employees retired from the company to form Unicomp to continue to produce buckling springs and Quiet Touch Model Ms based on the last generation designed by IBM and Lexmark. Since tooling had already been sold off back to IBM and Maxi Switch by the time of Unicomp's founding, the fledging company spent the rest of the '90s recovering Model M tooling from other Model M factories under IBM and Maxi Switch to rebuild its tool base[9]. By the turn of the millennium, Unicomp had established a wide range of keyboards and began the current era of the Model M. Unicomp continued to produce buckling spring Model Ms for IBM as late as 2004[10], and 2012 was the last year IBM marketed any Model Ms in their name as it sold its IBM Retail Store Solutions division to Toshiba[11] who then continued production of the Model M7 through M11 POS keyboards under their own name.

Design

Membrane circuitry

The single defining feature for all IBM keyboards with the designation "M" is their membrane assembly. Membranes are a form of circuit where traces (in this case, for the keyboard's matrix) are placed onto two thin sheets of plastic as a cheaper alternative to PCBs[12]. These traces will have contact points that allow a key to be registered when these contacts on both membrane sheets are pushed together. It should be noted that "membrane" does not mean the keyboards are necessarily rubber domes. The most famous mechanism placed on top of these in the Model M family is buckling springs, which the majority of famous and well-regarded Model Ms feature. It is argued by many whether this precludes the Model M from being a "mechanical keyboard", but the definition of the term is ambiguous and not standardised. So, it's best to avoid the term and simply consider the buckling spring Model Ms based on the merits of the auditory and tactile feedback they can provide, not the imperceivable circuitry underneath whose only functional drawback is a limit of two-key rollover.

Buckling spring key-switches

More information: IBM buckling spring#Membrane

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 by some) to hit the circuit underneath to make a connection. In the case of the Model Ms that feature buckling springs, pressing the switch will cause the flipper to bridge two contacts on the membrane sheets underneath at its given switch position[1]. This contrasts the buckling springs found on the earlier Model F keyboards that when buckling the capacitive material the flipper is made of is sensed by the capacitive sensing PCB underneath[14].

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 are rated for 25 million key presses and are also on the heavier feeling side of switches.

Alternative key-switches

More information: IBM buckling rubber sleeve

Contrary to common belief, not all Model M keyboards used buckling spring switches. Two other types of switches were employed on some Model M variants by the early 1990s. The most prolific is IBM buckling rubber sleeve, which was designed by IBM Information Products Corporation between 1990 and 1991[16] and saw its first deployment on the March 1991-launched[17] IBM Personal System/2 L40SX laptop keyboard assembly and its Model M3 numeric keypad attachment. The switch was subsequently deployed on the Models M4, M4-1, M6, M6-1, M7, M7-1, M8, M9, M11 and the "M-e" family of M7 to M11 successors. Buckling sleeve switches are markedly different to rubber dome switches in that the rubber component (the sleeve itself) sits external of the keyboard assembly and plays no direct role in actuating the membrane underneath. Instead, the sleeve is simply present to provide tactility and a return force. The membrane is instead actuated by rods protruding from the keycaps or a barrel slider depending on implementation. Both in theory allow for a more solid bottoming out key feel compared to a standard rubber dome over membrane switch.

Alternatively, some Model Ms in fact have a rubber dome variant. IBM, Lexmark and Unicomp marketed these as "Quiet Touch" keyboards, first introduced in 1993 with an IBM Enhanced Keyboard variant called the IBM Basic Keyboard (eg, P/N 71G4644)[18] and eventually used for some Model M2 and 122-key Model M variants. Today, Unicomp still offers a Quiet Touch option for most of its keyboards. The main technical difference is simply what's underneath the keycap - the buckling spring assemblies are replaced by rubber domes on a matt, however, most of the keyboard assembly and casing is otherwise identical. The keycaps are specially designed to press on a dome, meaning they cannot be reused with buckling spring models.

Technically speaking, it's possible to convert a Quiet Touch Model M to buckling spring by replacing the rubber dome matt with buckling springs and replacing all the keycaps with buckling spring ones.

Internal assembly

The vast majority of Model M keyboard assemblies are not monoblocks, instead featuring an inner keyboard assembly separate from the outer case. The typical Model M keyboard assembly is a sandwhich of the following distinct layers:

  1. The barrel plate: the top-facing layer used for guiding the key-switch components and keycaps to their correct positions atop of the membranes. They're typically called "frames" by OEMs such as Unicomp.
  2. The key-switch components: the membranes plus buckling spring-rocker assemblies or rubber dome matts, and usually a rubber/latex sheet (called a "blanket" by Unicomp) to protect the membranes from stress.
  3. The backplate: the metal on the back used for support, typically curved to provide the sculpt for the uniprofile keycaps.

Model M assemblies are typically riveted together in some way to provide security of the inner switch technology with tension. Typical buckling spring Model Ms famously use melted plastic rivets. The longevity of these rivets has been called into question as they can invariably break off over the years and decades. Losing a handful of rivets that are not adjacent to each other is generally not fatal, but losing many that are clustered in one area of the keyboard will lead to a loss of tension that can at first lead to mushy-feeling keypresses and then will stop registering as it gets worse. It's impossible to establish the cause from case to case, but some generally believe they can break with a combination of extreme and/or sustained vibration, humidity and the user's handling of the keyboard.

The good news is that a chronic loss of rivets typically does not mean the keyboard cannot be salvaged. Practises known as screw or bolt modding can be used to replace the lost rivets with screws or bolts (respectively) to regain tension on the assembly. This can be done yourself (guides on how to do this like Bitten's Model M Restoration Megaguide exist) or can be professionally done by experienced 'bolt modders' such as long-time practitioner Brandon @ clickykeyboards.com. It should also be considered that many vintage Model Ms from the 1980s continue to operate with their original rivets intact, and indeed many Model Ms exchange hands between owners without issue.

As for non-buckling spring Model Ms such as those with buckling rubber sleeve switches, the method of riveting varies. Model M4 and M6 buckling sleeves keyboards use metal 'teeth' rivets that hook the backplate onto the barrel plate. This solution avoids perishable plastic and allows the backplate to be easily removed from the rest of the keyboard. Models M3, M4 and M4-1 numeric keypads however use plastic rivets. Models M7, M7-1 and M8 avoid rivets entirely and use screws.

PBT dye-sublimated keycaps

Beige Model Ms are known for their high-quality unique-mount PBT dye-sublimated keycaps, something inherited from the Model F family. Versus the most common keycap material, ABS[20], PBT is more durable, does not degrade/yellow with age, UV or heat exposure, and will keep its texture for longer without shining[21]. 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.

Most buckling spring, buckling sleeve and Quiet Touch Model M 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 M to have innate layout customizability without the user needing to worry about mismatches in keycap sculpting - sculpture is instead provided by the curved internal keyboard assembly (or the keyboard is intended to be low and uni profile, such as with Models M1, M2, M3, M4 and M6). Furthermore, most buckling spring Model Ms 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, not all buckling spring Model Ms have two-piece keycaps, with notable exceptions include the Models M1, M2, M13 and M15, and some models that are known to have two-piece keycaps may come with single-piece keycaps due to manufacturing nuances over the years. Since 2020, Unicomp seems to now only focus on manufacturing single-piece keycaps.

Beige and industrial coloured Model Ms receive two colours of keycaps; off-white (also known as pearl) and grey (pebble). Black Model Ms with all-black keycaps have pad-printed (perishable) white lettering since dye sublimation cannot be used to sink in dye lighter than the host plastic without resorting to a more costly inverse dye sublimation technique. 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[22].

Rear labels

One of the hallmarks of the Model M family is strong documentation of the keyboard's type and date of manufacture in the form of a rear label sticker casually referred to as a 'birth certificate'. This feature is something also inherited from the Model F family and has been present since the first Wheelwriter keyboard assemblies were produced and are still found on the latest Toshiba POS or Unicomp buckling spring Model Ms. Model M keyboards can have an external label and an internal label.

External rear labels

The external rear label is used to display information about the keyboard as a whole. As a summary of the main data points of interest presented on the external rear label:

There are many variations of these birth certificates from various eras of production or manufacture. A sample can be seen below but note there are many more as well.

Internal rear labels

As briefly mentioned above, the internal keyboard assembly (of Model Ms that are not a unibody design) can have their own part number with their own rear-facing label. Actionwriter, Quietwriter and Wheelwriter keyboard assemblies typically also have their only birth certificate on the back of the keyboard assembly. The internal rear label is used to display information regarding just this inner assembly along with the keycaps fitted to it as standard. It doesn't represent the type of controller, lock-lights or outer case of the whole keyboard. As such, multiple unique outer part numbers can share the same internal part number as evidenced by the fact the US ANSI layout IBM Enhanced Keyboards P/N 1390120 (PC/XT)[23], P/N 1390131 (PC/AT)[24] and P/N 1391401 (PS/2)[25] can all bear the inner assembly part number P/N 1386085 since the differences between those three models don't include the keyboard assembly itself or the keycaps.

As a summary of the main data points of interest presented on the internal rear label:

Once again, a sample of these rear labels can be seen below but keep in mind that various other styles exist. Another thing to note is that internal rear labels have been known to be substituted with information written directly on the keyboard's backplate, especially for US-produced Model Ms in the 1990s.

Keyboards

Type
Production/‎ marketed
Key ‎switch
Icon
1984-2001
Buckling spring
1985-present
Buckling spring, Quiet Touch rubber dome
1986-?
Buckling spring
1986-2006
Buckling spring
1987-1996
Buckling spring
1987-1996
Buckling spring
1989-present
Buckling spring, Quiet Touch rubber dome
1990-1999
Buckling spring, Quiet Touch rubber dome
1991-1992
Buckling rubber sleeve
1992-2010
Buckling rubber sleeve
1992-present
Buckling spring
1992-1998
Buckling rubber sleeve
1993-2014
Buckling rubber sleeve
1993-?
Buckling rubber sleeve
1993-2014
Buckling rubber sleeve
1993-2014
Buckling rubber sleeve
1993-?
Buckling rubber sleeve
1993-2008
Buckling spring
1994-1996
Buckling spring
1994-?
Buckling spring
2000-present
Buckling spring
2000-????
Buckling rubber sleeve
2001-????
Buckling rubber sleeve
2002-????
Buckling rubber sleeve
2007-present
Buckling spring
2008-present
Buckling rubber sleeve
2008-present
Buckling rubber sleeve
2008-present
Buckling rubber sleeve
2011-present
Buckling rubber sleeve
2020-present
Buckling spring
2021-present
Buckling spring

Model M-based typewriter keyboard (1984)

The first membrane buckling springs keyboards were in fact the keyboard assemblies for the 1984-debuting IBM Wheelwriters 3 and 5 and Quietwriter 7. What would become the Model M as we know them featured on all subsequent IBM and later Lexmark Wheelwriters for the next decade. The layouts of these keyboard assemblies were vaguely PC-like, with a mix of including T-nav arrow keys, one or two columns of left-side function keys, and occasionally even a numeric keypad being found on various models depending on their value segment. As a result, most Wheelwriter keyboards range from approximately 65% to 80% size layouts. The common feature amongst all of them was a split spacebar with the smaller "Code" key being an additional modifier for accessing functions throughout the keyboard. Wheelwriter keyboards were produced for the entire IBM and Lexmark eras of Model M history, with examples produced as late as 2001 possibly by Unicomp[28].

Enhanced Keyboard (1985)

More information: Model M Enhanced Keyboard

The Enhanced Keyboards are the most well known and definitive Model M variants, being IBM's premier keyboard design for about a decade after its release. Its first introduction in 1985 was the Industrial Keyboards for the AT-class IBM 7531 Industrial PC, closely followed by the IBM 3161 ASCII Display Station Keyboard. These introduced the eponymous Enhanced keyboard layout - which became industry standard and is still used today with the addition of GUI keys - and the typical design features the Model M is known for. The following year, the first PC-orientated models were released for PC/XT and PC/AT systems. IBM PS/2 computers debuting in 1987 helped propel the Model M into stardom and paved the way for the Enhanced Keyboard to become perhaps the most recognisable keyboard of all time. The Enhanced Keyboard also made its way to other IBM terminals such as the 3151, 3192, and various InfoWindow Display Stations. A Quiet Touch rubber dome version was also made available called the IBM Basic Keyboard. Other distinct variants exist for other types of systems and custom orders from third-party companies such as CompuAdd, Dell, General Electric Healthcare, Sabre and Wang. Versions of this keyboard were also produced with Lexmark and Unicomp branding, the latter of which remains in production today as the Unicomp Classic. Essentially, if someone says "Model M", they're usually referring to this keyboard.

122-key Type I & Type II terminal keyboards (1985)

The 122-key terminal keyboards (commonly known as "M122s" today) are the largest Model Ms available although they are a nuanced subfamily of keyboards themselves. The M122s started out as the membrane buckling springs adaptation of the 122-key Model F design and thus heavily resemble them and were made for use with many of the same terminals including the IBMs 3179, 3180 and 3205. However, these original Type I M122s with Model F-style two-setting riser feet and straight shaped 240-degree pin arranged DIN plug were followed by three further revisions and modifications to the design. Type II was introduced not long after Type I and largely look the same, except that it has Model M-style flip-out feet and a right-angle shaped DIN plug. Type I and II are also typically referred to as "battleship" keyboards due to their size.

4683/4684 Alphanumeric POS Keyboard (1986)

The IBM 4683/4684 Alphanumeric POS Keyboard is presently the only known bucklin spring point of sale input device released by IBM. They were made for use with IBM's first PC-based POS system, the PC/AT based IBM 4683 POS Terminal. The keyboards themselves have an AT layout and their inner assemblies seems to be based on IBM Wheelwriter keyboard assemblies. The layout makes them a sort of "Model M/AT", if you will.

Space Saving Keyboard (1986)

More information: Model M Space Saving Keyboard

The Space Saving Keyboards (SSK) are perhaps the most well-known Model M variation over the Enhanced Keyboard. They are a tenkeyless compacted version of said Enhanced Keyboard, first available as a terminal keyboard and later as an option for all or included with some IBM PS/2 computers. Due to the fact numeric keypads were viewed more favourably during the 1980s, the SSKs are relatively rare. Industrial grey versions of the SSKs are known and were popular in the automotive industry during the early 1990s. The SSK exited actual production by 1999, however, Unicomp continued to sell the keyboard into the 2000s using leftover parts from the previous decade. In 2021, the SSK was spiritually succeeded by the Unicomp Mini Model M.

Screen Reader/2 Keypad (1987)

The IBM Screen Reader/2 Keypads were the peripheral components of the IBM Screen Reader/2, the first GUI-based screen reader designed to help people with hard or lack of sight access a PC. The keypad takes the form of an 18-key PS/2 compatible buckling springs keypad. These are one of two Model Ms whose internal assembly is based on an older Model F device and thus takes several production values from Model F designs; individual barrels, metal barrel plate, foam padding, and no plastic rivets holding the assembly together. The assembly's previous incarnation was the 25-key IBM 3290-1 Information Panel Program Function and Numeric Keypads.

50-key Keyboard (1987)

The 50-key Model Ms ("M50s") were a matrix-style keypad primarily used with emulating IBM 4700 applications on IBM Personal System/2 or similar class machines. They possessed the same physical layout as the 50-key Model F-based IBM 4704 Model 100 keypads and could come with transparent, functional or alphameric legends. Technically speaking, these are the smallest Model Ms capable of featuring an alphameric layout, although the triple segmentation of the keys makes using an M50 for typing difficult. These are one of two Model Ms whose internal assembly is based on an older Model F device and thus takes several production values from Model F designs; individual barrels, metal barrel plate, foam padding, and no plastic rivets holding the assembly together. The assembly's previous incarnation was the aforementioned 50-key Model F IBM Model 100s these M50s replaced.

Type III & Type IV 122-key terminal keyboards (1989)

The Type III and IV M122s were slightly compacted and lighter follow-ups to the Type I and II "battleship" M122s. Typically referred to as "battlecruisers" to differentiate them from their older/larger counterparts, Type III was also a terminal keyboard, however, it sported design language closer to other Model Ms and typically found their home with IBM InfoWindow Display Stations and connected via a modular 8P5C ("RJ-45"-like) connection. The Type IV M122s were introduced soon after as a PC-compatible variant of Type III with lock-lights and at first modular SDL-based cables for use with terminal emulation. Unicomp's PC 122 family is essentially an evolution of Type IV with fixed cables.

M1/M2 Selectric Touch Keyboard (1990)

The Model M1s and M2s were lightweight alternatives to the Enhanced Keyboard. Whilst they mostly used the same buckling spring actuators as their brethren, almost everything else about the design was changed as they have no metal backplate, an integrated front cover and barrel plate, and a completely different logic board featuring surface-mounted components. The M1/M2 physical design was patented in October 1989 as USD330199S[35] and the earliest production examples seen are from 1990[36]. The difference between the M1s and M2s are that the M1 was sold as a standalone product under the "Easy OPTIONS by IBM" brand and the M2 was bundled with full computer systems (usually, IBM Personal System/1 series of low-end home computers). Otherwise, M1s and M2s are the same keyboards. An IBM 3153 terminal and a "bordered" IBM EduQuest variant of the M2 also existed, as well as Quiet Touch rubber dome versions. Despite the name, these keyboards have no relation to the IBM Selectric electric typewriters. Lexmark self-branded versions were marketed as the Easy Touch (Quiet Touch) and Streamlined (buckling spring) Keyboards[37].

M3 numeric keypad & laptop keyboard assembly (1991)

More information: Model M3 PS/2 L40SX Numeric Keypad

The Model M3s were the first major deviations from the expected buckling springs keyboards of the previous types. The keyboard design was introduced with the IBM Personal System/2 L40SX in March 1991[17], which was an early laptop that featured IBM's first buckling rubber sleeves keyboard assembly. It could also be had with an optional numeric keypad that used the same switches and was designated Model M3. The IBM PS/2 CL57SX and PS/55 N27sx also used variants of this keyboard design. The keyboard assembly was later reused for the Model M4 family and was spiritually succeeded by the ThinkPad's Model M6 series keyboard assemblies.

M4/M4-1 Space Saver Keyboard & numeric keypad (1992)

More information: Model M4 & M4-1 Space Saver Keyboard, IBM Model M4 & M4-1 Space Saver Numeric Keypad

The Model M4s were the discrete desktop and server environment adaptations of the L40SX keyboard and numeric keypad Model M3 assemblies. The M4's physical design was patented in December 1991 as USD344724S[40] and the earliest production example seen is from February 1992[41]. The M4 is a straight adaptation of the L40SX assembly, featuring a PS/2 based controller. The M4-1 on the other hand adds a TrackPoint II pointing stick module, making it the first IBM keyboard with a TrackPoint. All M4s use the same buckling rubber sleeves switches as their M3 predecessors. M4s were originally produced by Lexmark then Key Tronic after April 1996, but Unicomp continued production until the late 2000s as the Unicomp Mighty Mouse keyboards. A companion Model M4 or M4-1 numeric keypad was available for all M4s.

M5-1/M5-2 Trackball Keyboard (1992)

The Model M5s were variants of the Enhanced Keyboard with integrated trackball modules. The M5-1 and M5-2 were introduced at the same time by February 1992[43], with the M5-1 featuring a 16mm trackball placed around the arrow keys and the M5-2 featuring a 25mm trackball placed on the top-right corner of the keyboard. The M5-1 did not continue in production for long, but the M5-2 is still in production via Unicomp; first branded as the Unicomp On-The-Ball and later/currently the Unicomp Classic Trackball. The Lexmark era models were the last Model M variant released that featured modular SDL connection. Unicomp has since moved to using fixed cables for them just like their other keyboards.

M6/M6-1 ThinkPad Keyboard Assembly (1992)

The Model M6s were a wide range of IBM portable computer keyboard assemblies largely introduced by the IBM ThinkPad 700 in October 1992 and then subsequently used with most major ThinkPad models for the following 3 years. They were refined Model M3 keyboards using the same buckling rubber sleeves switches but the keyboards themselves had reduced form-factor bodies and the keycaps used a different mount. The biggest difference between M6 and M6-1 was the key barrel slider's colour; M6 had brown sliders, M6-1 had black. Other differences included a larger membrane matrix on the M6-1 (hence the larger ribbon cables) and how they mounted into the host computer. M6s were exclusively produced by Lexmark, however, M6-1s could be produced by Lexmark (before April 1996) or Key Tronic (after). They were used in a plethora of ThinkPads like the 365, 500, 750C, 755CX, 850 and 860, and also used with Lexmark's own Lexbook laptop brand and several laptops they manufactured for other companies. However, by the late 1990s, these had been succeeded by scissor-switch keyboards produced by various other OEMs. Whilst some of these may look identical, the official M6 designation was dropped.

M7 50-Key POS MSR Keyboard (1993)

More information: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards#M7

The Model M7 is a 50-key point-of-sale systems keypad with an integrated magnetic stripe reader. It was the successor of the non-Model M family IBM 468x series keypads of similar function for the IBM 469x family and later many other retail systems from IBM and Toshiba. It's earliest host system was the IBM 4694 POS Terminal Model 001 announced in June 1993[44]. For the most part, the layout and function of the M7 are customisable and the keypad has many transparent keytops to facilitate printed or written legends on paper. However, almost all M7s have a dedicated numeric keypad in the middle key bank and a Ctrl key in the top-left. These use IBM buckling rubber sleeve key-switches.

M7-1 50-Key POS Keyboard (1993)

More information: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards#M7-1

The Model M7-1 is a 50-key point-of-sale systems keypad without an integrated magnetic stripe reader, the defining difference between this M7-1 and the M7. It too was the successor of the non-Model M family IBM 468x series keypads of similar function for the IBM 469x family and later many other retail systems from IBM and Toshiba. It's earliest host system was also the IBM 4694 POS Terminal Model 001 announced in June 1993[44]. For the most part, the layout and function of the M7-1 are customisable and the keypad has many transparent keytops to facilitate printed or written legends on paper. However, almost all M7-1s have a dedicated numeric keypad in the middle key bank and a Ctrl key in the top-left. These also use IBM buckling rubber sleeve key-switches.

M8 50-Key POS LCD Keyboard (1993)

More information: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards#M8

The Model M8 is a 50 key point-of-sale systems keypad that is very much like the M7 but sports a tilt-adjustable LCD panel and always has an integrated magnetic stripe reader. It's earliest host system was also the IBM 4694 POS Terminal Model 001 announced in June 1993[44]. Like the M7, for the most part, the layout and function are customisable and the keypad has many transparent keytops to facilitate printed or written legends on paper. However, almost all have a dedicated numeric keypad in the middle key bank and a Ctrl key in the bottom-right. These also use IBM buckling rubber sleeve key-switches.

M9 ANPOS Keyboard (1993)

More information: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards#M9

The Model M9 is a 116-key (US English) or 117-key (rest of world) alphanumeric point-of-sale (ANPOS) systems keyboard. It's earliest host system was also the IBM 4694 POS Terminal Model 001 announced in June 1993[44]. The keyboard has two distinct types of keys - the 60%-size alphanumeric standard keys and the transparent keytop keys the Models M7, M8 and M11 use. Like its siblings, a dedicated numeric keypad is found within the transparent-topped keys and gives enough spacing between the alphas and itself to allow for a full Enhanced layout configuration if desired. Of note is that US English layout M9 comes with an ANSI-style left shift and ISO-style enter keys as part of its layout. M9s are only available with an integrated magnetic stripe reader and also use IBM buckling rubber sleeve key-switches.

M11 POS Modifiable Layout Keyboard (1993)

More information: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards#M11

The Model M11 is a 133-key point-of-sale systems matrix keyboard or "key array". It's earliest host system was also the IBM 4694 POS Terminal Model 001 announced in June 1993[44]. It's an ortholinear spin on the Model M9 design. Other than the dedicated numeric keypad and Ctrl key, this device can be entirely used for functional/macro use however, ortholinear alphanumeric layouts have also been spotted. M11s are only available with an integrated magnetic stripe reader and also use IBM buckling rubber sleeve key-switches.

M13 pointing stick keyboard (1993)

The Model M13 was a variant of the Enhanced Keyboard with an (at-first) integrated TrackPoint II strain gauge-based pointing stick. They first appeared in Lexmark advertising sometime between May and November 1993[48][49] with major production observed from the following year. The M13 in a similar fashion to the SSK is one of the most well-known Model M variants and the black version is well sought after. M13s could also come with a PS/2 passthrough port for mice on the back and have noticeably stronger case texturing compared to almost every other Model M. Unicomp continued producing the M13 until around 2009, branding the keyboard as the Unicomp On-The-Stick and using their unique force-sensing resistor based pointing stick. An industrial version of the M13 also exists.

M15 Select-Ease Keyboard (1994)

The Model M15 was a highly adjustable ergonomic tenkeyless-like keyboard based on the Model M1/M2 design and was branded as either the IBM Adjustable Keyboard, OPTIONS by IBM Adjustable Keyboard, or Lexmark Select-Ease Keyboard. Being the only ergonomic keyboard as per today's standards that IBM ever marketed, the Model M15 features a high degree of customisability; including split, tilt, swivel and tenting capabilities. For convenience, the arrow keys are duplicated on both halves of the keyboard and the split spacebar has an Erase-Eaze feature. A companion numeric keypad (also designated Model M15) could also be had and connected to the host keyboard via a proprietary connection. It is a candidate for the last IBM-sanctioned buckling springs keyboard design.

5576-C01 (1994)

The 5576-C01 was a Japanese-only Model M offshoot produced solely for the IBM PS/55E all-in-one computer. These use modified buckling spring switches that are said to feel slightly different to other Model Ms. These also feature a highly unique rotating vertical stand that allows you to park the keyboards upwards on its back wall. These use TrackPoint II like its larger Lexmark or Maxi Switch produced Model M13 siblings. They could also come in proprietary combined signal PS/2-like cable or a more standard Y-split keyboard and mouse PS/2 cable. It is a candidate for the last IBM-sanctioned buckling springs keyboard design.

Unicomp EnduraPro (2000)

The EnduraPro is Unicomp's spiritual successor to the Model M13 and was their first self-introduced Model M variant. The EnduraPro is an adaptation of the IBM 5576-C01 tooling and thus both closely resemble each other. However, the vertical stand feature has been removed and the TrackPoint II pointing stick has been swapped out for Unicomp's own force-sensing resistor based implementation. Unicomp's typical layout options are also available. After two decades of production with the same tooling, the moulds used to produce them are prone to producing defects.

"M-e" 4820 32-Key POS Keypad (2000)

The monitor-mounted IBM SurePoint 4820 Keypad was the first of the Model M "extended family" (M-e) POS input devices, an undesignated extension of the Model M Retail POS keyboard family (Models M7 through M11) introduced by September 2000. This 32-key keypad was the smallest member of the "M-e" family typically mounted on the right side of various IBM SurePoint POS touchscreen monitors. In its default layout, 31 of the 32 keys are individually discrete, typically featuring a numeric keypad with a zero key taking up two key positions (hence 31) and a Ctrl key on the lower 4x4 key bank. Examples with or without an integrated magnetic stripe reader are known. Like the RPOS family this keypad extends from, it uses IBM bucking rubber sleeves key-switches.

"M-e" PS/2 ANPOS Keyboard (2001)

The IBM PS/2 ANPOS Keyboard with Integrated Pointing Device was an M-e enhancement of the Model M9 RANPOS Keyboard design, thus occasionally referred to as the M9-e in fan circles. For the most part, the M9 and M9-e are virtually identical save the integrated force-sensing capacitor based Synaptics TouchStyk pointing stick referred to as simply "POS pointer" in marketing. As such, it too has two distinct types of keys, an integrated magnetic stripe reader, and was available in 116-key (US English) and 117-key (rest of world) layouts. It also uses IBM bucking rubber sleeves key-switches.

"M-e" CANPOS Keyboard (2002)

Unicomp SpaceSaver/Ultra Classic (2007)

The Ultra Classic (also known as the SpaceSaver M for the Mac version and previously called SpaceSaver itself) was Unicomp's sole save-saving no-frills alternative to the Unicomp Classic before the introduction of the New M and Mini M. It is a sibling to the Unicomp EnduraPro as it is made with the tooling formerly used to produce IBM 5576-C01 keyboards. Unlike the EnduraPro, these do not have an integrated pointing stick. However, like the EnduraPro, the moulds used to produce them are old and are producing defects.

"M-e" Modular ANPOS Keyboard (2008)

More information: Model M-e Modular 67-Key POS, MANPOS & MCANPOS Keyboards#MANPOS

The Modular ANPOS Keyboard (MANPOS, aka ANPOS II) is the direct successor to the original M-e based PS/2 ANPOS Keyboard. Being an Modular POS series device, the MSR and key lock are now attachments instead of fixed components and the design now gains a touchpad compared to a PS/2 ANPOS Keyboard or any pointing device compared to an M9. In terms of layout modification, the changes are tame - only 3 programmable keys have moved to make way for the pointing module, thus is likewise available in 116-key (US English) and 117-key (rest of world) layouts. The status indicators panel is also much smaller now. Like its predecessor, it uses IBM buckling rubber sleeves key-switches. Since 2012, these have been produced and branded by Toshiba TEC.

"M-e" Modular CANPOS Keyboard (2008)

More information: Model M-e Modular 67-Key POS, MANPOS & MCANPOS Keyboards#MCANPOS

The Modular Compact ANPOS Keyboard (MCANPOS, aka CANPOS II) is the direct successor to the original M-e based CANPOS Keyboard. Like CANPOS, MCANPOS fits a full-size keyboard and many programmable keys in a chassis that is a similar width to a tenkeyless keyboard. Additionally, all alphanumeric keys are slightly thinner compared to their M9 ANPOS, M-e PS/2 ANPOS and M-e MANPOS counterparts. MCANPOS made many of CANPOS's features modular but it also added the possibility of a key lock and a touchpad that the original CANPOS could never have. No extra keys were added despite some programmable key layout alterations, meaning both CANPOS and MCANPOS have 133 (US English) or 134 (rest of world) keys. Extra status indicators were also added; CANPOS only had three keyboard lock-lights, MCANPOS adds a "Wait", "Offline", "Message Pending" and a user-definable light. Like its predecessor, it uses IBM buckling rubber sleeves key-switches. Since 2012, these have been produced and branded by Toshiba TEC.

"M-e" Modular 67-Key POS Keyboard (2008)

More information: Model M-e Modular 67-Key POS, MANPOS & MCANPOS Keyboards#M67POS

The Modular 67-Key POS Keyboard is the direct successor to the Model M7 and M7-1 50-key POS Keyboards and thus occasionally referred to as the M7-e in fan circles. As its name implies, the M7-e adds 17 keys over its predecessor, however, these new keys are arranged around the same basic layout as the original 50-key M7 to allow for some familiarity for IBM's customers upon upgrading and preserve application-level compatibility. Also included from the M7 design is a dedicated Ctrl key that cannot be reprogrammed and same numeric keypad with a double-width 0 key by default, giving the design 65 total programmable keys out of the box. Being an Modular POS series device, the MSR and key lock are now modular attachments instead of fixed components. Like its predecessor, it uses IBM buckling rubber sleeves key-switches. Since 2012, these have been produced and branded by Toshiba TEC.

"M-e" Modular 67-Key POS LCD Keyboard (2011)

More information: Model M-e Modular 67-Key POS, MANPOS & MCANPOS Keyboards#M67POSLCD

The Modular 67-Key POS LCD Keyboard is the direct successor to the Model M8 50-key POS LCD Keyboard and thus occasionally referred to as the M8-e in fan circles. As its name implies, the M8-e adds 17 keys over its predecessor, however, these new keys are arranged around the same basic layout as the original 50-key M8 to allow for some familiarity for IBM's customers upon upgrading and to preserve application-level compatibility. Also included from the M8 design is a dedicated Ctrl key that cannot be reprogrammed and same numeric keypad with a double-width 0 key by default, giving the design 65 total programmable keys out of the box. Being an Modular POS series device, the MSR and key lock are now modular attachments instead of fixed components. Like its predecessor, it uses IBM buckling rubber sleeves key-switches. Since 2012, these have been produced and branded by Toshiba TEC.

Unicomp New Model M (2020)

The New M was the first true new buckling spring Model M variant introduced in 20 years, made with new tooling and thus not prone to the dimples and blemishes Unicomp's older products suffer with. It's essentially the successor to the Unicomp Ultra Classic, taking up a market position of being a bezel-reduced Model M compared to the IBM Enhanced Keyboard/Unicomp Classic. Stylistically, the New M is much closer than its predecessor to typical Model M design features. It is presently only available in black.

Unicomp Mini Model M (2021)

The Mini M is the successor to the SSK and is presently the latest Model M variant. Compared to the original SSK, the Mini M sports an upgraded membrane matrix capable of many 6-10 key combinations, lock-light LEDs, a modular and pressure-locking Type-A USB interface, and is available (and only) in black. The left/right bezel footprint is also slightly diminished compared to the SSK. Like the New Model M, this keyboard is built with Unicomp's latest tooling and thus not prone to the dimples and blemishes Unicomp's older products suffer with.

Further reading & resources

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