Battleship? Battlecruiser? Those are the two terms we have typically come to use when differentiating between 122-key Model Ms. However, as some may know, there are quite a few nuances that get overlooked when using such a 'binary' classification, which in my opinion, groups the similar-looking but measurably different keyboards together too broadly. When it came time to design my database, I settled on a four-type classification system to group the major Model "M122" variants in a way that I hope will provide a still-simple yet more accurate means to identify specific M122s. This page describes the four types in good detail and with some helpful photos and illustrates how the earlier ones that resemble the older 122-key Model Fs differ from them.
Note: Please keep in mind that exceptions to what is described may exist - IBM and family made a lot of variation amongst its products over the years, and keeping track of them can be difficult. This page is best used as a quick reference for the majority of 122-key Model Ms. Also of note is that these 'types' are not a replacement or alternative to the 'generations' some may refer to. Generations group and describe production quality differences such as the keyboard assembly's backplate thickness (something obscured from an external visual standpoint), whereas these types group and describe feature compliment irrespective to production quality changes. Where possible, I've mapped the type to the most likely generations they encompass.
All 122-key Model Ms can trace their origins to the 122-key Model F. Being also a buckling spring keyboard, the so-called F122 heavily resembles the first two types of 122-key Model M. This includes what's a virtual identical top case piece, same IBM branding, and the same style of flip-out riser-style feet, thick coiled cables with metal-jacketed 240-degree DIN connectors at the end, and use of stepped modifier keycaps as the Type I 122-key Model M. 122-key Model Fs can also have either "Cmdxx" or "PFxx" nomenclature 24-key function block keys just like the Type I and II 122-key Model Ms. The only sure way to tell a 122-key Model F and Type I Model M keyboard a part is the bottom case piece:
The 122-key Model F was first employed as the IBM 5271 Converged Keyboard Assembly for IBM 3270 PC in late 1983. It later saw use with IBM 3179, 3180 and 3205 terminals.
The first 122-key Model Ms were perhaps the most conservatively designed Model Ms ever released. Type I is virtually identical to the aforementioned 122-key Model Fs that came before them from a top, front, rear and side perspective. The Type I has two-setting riser-style feet, thick coiled cables with metal-jacketed 240-degree DIN connectors at the end and either "Cmdxx" (or "Mdtxx" for Spanish keyboards) or "PFxx" nomenclature 24-key function block keys, all design traits retained from the 122-key Model F design. Type Is are also the most likely 122-key Model M to have a bank of DIP switches at the bottom too. Finally, Type I was almost exclusively produced to first-generation Model M specifications and thus should have a rainbow-looking heat-treated steel backplate.
The Type I seems to have been originally introduced for the IBM 3205 Color Display Console as the "membrane" keyboard option for the system (a Model F "capacitance" option was also available), however, the keyboard was used with the IBM 3179, 3192 and 3193 Model 1 display stations and some later versions of the 5271/5273 keyboards for IBM 3270 PC family.
Type II 122-key Model Ms are an evolution over Type I, once again looking like a 122-key Model F but now featuring a few more visual distinctions. For starters, gone are the side-accessible riser-style feet - Type II have typical Model M-style flip-out feet that are accessible from the bottom. However, the feet the Type II has (and the other following types have) are longer than those found on other Model Ms such as the Enhanced and Space Saving Keyboards. The typical Type II also lacks any stepped keycaps where a PC keyboard's modifiers would reside and the DIP switch bank underneath is unpopulated, but examples with one or both of these are known to exist. The final difference is that the connector's design is different - whilst it's still a 240-degree DIN plug, the metal jacket is replaced with a plastic jacket and the plug also has a 90-degree angle. Type II was largely produced to first and second-generation Model M specifications and thus could have either a heat-treated or a grey steel backplate.
Type II is generally associated with the IBM 3196 and 3197 Display Stations, however, they were also employed with the IBM 3191 Display Station and 3206 Console Display Terminal.
Type III 122-key Model Ms are radically different compared to its predecessors. They are instantly and easily identifiable since they feature a completely different case design that's distinctly Model M as opposed to being a mere internal rework of a 122-key Model F. The Type III features the distinct Model M wedge shape, slimmer bezels for the case's side edges to the key, smaller surface area around the 24-key function block, exclusively features the said 24-key block with "Fxx" numbering scheme as standard, and adds a three-way cable router to the underside. The connector is also different, being a modular 8P5C design (ie, the same physical jack as RJ-45/ethernet). In line with pretty much all Model Ms from 1987 and onwards, the silver square IBM logo was swapped for oval-style logos; originally with grey IBM text, later with blue text. Whilst no Type IIIs had lock-lights, some Type IIIs could have a visible location for lock-lights in the form of a blanking plate on the top-right corner. Early UK-produced Type IIIs typically lacked any trace of lock-lights, however, US-produced ones seemed to always have the blanking plate present (likely since they shared tooling with the Type IV mentioned below). Type IIIs were generally made to second and third-generation Model M specifications, meaning they could only have grey steel backplates and will feel noticeably lighter than Type I and II. Very late IBM UK or Unicomp produced examples could be made to fourth generation specs.
Type IIIs are best associated with the IBM InfoWindow family of terminals.
The Type IV 122-key Model M is simply a PC-compatible version of Type III. They feature all the design cues Type III has over the first two types, but Type IVs typically have lock-light LEDs due to their PC compatibility and IBM or Lexmark produced examples also had a modular SDL connector on the back that could accept either 180-degree DIN (AT-style) or mini-DIN (PS/2) cables. Another remarkable feature is the presence of dual dye-sublimated legends, which feature the terminal orientated and universal legends as the primary black-coloured legends with a subset of PC-centric legends as secondary blue-coloured legends.
IBM called these keyboards PS/2 Host Connected Keyboards and were used for terminal emulation on PS/2 or similar/later systems.
Unicomp continues to produce keyboards based on the Type IV design, for companies that require such keyboards for IBM 3270 or 5250 terminals or terminal emulation on modern systems, or for consumers wishing a 122-key fully PC compatible keyboard. They are not much different compared to Type IV proper (hence my lack of distinct classification), but there are some differences worth mentioning. Unicomp produces their 122-key keyboards in three distinct versions that they used as branding names:
The 122 Terminal keyboards are best described as an updated Type III design that lack lock-lights and may feature full-size DIN plug or modular 8P5C jacks, whereas the other two are proper Type IV continuations complete with lock-lights. Both 122 Emulator and PC 122 no longer sport detachable cables, however, the PC 122 is available in a USB flavour. Unicomp also allows rudimentary firmware customisation from the factory, and in the past, Unicomp has also offered attachments like a magnetic stripe card reader for those wanting a 122-key keyboard on their POS terminals. This means there's a lot of diversity to Unicomp's 122s, and technically means there's a possibility that two given Unicomp 122s may behave differently to each other. The final detail worth mentioning is that Unicomp is well known for producing keyboards for other companies, as such, you can find many Unicomp 122s with other companies branding - Affirmative, BOS, Data Decision and I-O are amongst the most well-known companies that sell/sold their own branded Unicomp 122s.