×

Model M Space Saving Keyboard

Also applies to Lexmark Spacesaver Keyboard and Unicomp 85 Key Space Saver

Contents

Background

IBM Space Saving Keyboard
IBM Space Saving Keyboard

The IBM Space Saving Keyboard was the small form-factor counterpart to IBM's flagship Enhanced Keyboard marketed between 1986 and 1999. Commonly referred to as the "SSK", the Space Saving Keyboard is probably the most famous tenkeyless keyboard of all time and most modern tenkeyless keyboards can trace their heritage to it. Like its larger brethren, the SSK is known for sporting clicky buckling spring key-switches and high-quality dye-sublimated PBT keycaps.

The SSK is a member of the large Model M family of keyboards and is likely its most well-known non-101/102 key variant. Whilst not a flagship keyboard, it's still well regarded and closely tied with the IBM Personal System/2 family of computers. That said, it also found itself with a high number of variations beyond the typical PC-style design and layout for terminals, airline reservation systems, financial systems and even automotive maintenance systems. At least 30 SSK part numbers have been documented.

Specifications

Marketing names
IBM Space Saving Keyboard, Lexmark Spacesaver Keyboard, Unicomp 85 Key Space Saver
OEM(s)
IBM, Lexmark
Designation
M
Family
Keycaps
Dye-sublimated PBT
Case dimensions
40.6cm x 19cm x 5.8cm (15.98" x 7.48" x 2.28")
Case material
PVC
Case colour(s)
off-white (pearl white) or industrial grey
Case screws
5.5mm (7/32") hexagonal
Weight
1.9kg[3] (~4.2 lbs)
Layout
84 (ANSI) or 85 (ISO) key tenkeyless
Connectivity
PS/2 or terminal
Successor
IBM Space Saver Keyboard (indirect), Unicomp Mini Model M (spiritual)

History

The SSK was amongst the earliest Model M variants introduced, preceded by just Model M-based typewriters, the Enhanced Keyboard and the Types I and II 122-key terminal keyboards. The first SSK announced was the 84-key space-saving "shorter keyboard" for the IBM 3162 ASCII Display Station in September 1986. Its part number was 1391518 and its planned availability was October 1986 for 3162 models 310 and 320 and Q1 1987 for 3162 models 410 and 420[1]. Very few records of this early SSK exist, but it's believed it had a 240-degree pin arranged DIN plug and would be the only production SSK made to first-generation Model M specifications. The first SSK of which photos are available is the IBM 3151 ASCII Display Station Space Saving Keyboard (P/N 1392980), launched in June 1987 and was available for 3151 models 110 and 160[2].

Despite the existence of these terminal models, SSKs are almost entirely associated with the IBM Personal System/2 series of PCs. Some specific PS/2 models had SSKs bundled with them or at least had an SSK option made available, giving the SSK its largest and most famous utilisation. Starting with the PS/2 Model 25 models 001 and 004 in August 1987[3] then at least followed by the Model 40 SX in June 1991[4], Model 35 SX in October 1991[5], Model 57 SLC in August 1992[6] and Model 95 XP 486 in September 1992[7]. A version of the PS/2 SSK (P/N 1392464) was also used for the PS/2 Model 30-based IBM 6901 Personal Typing System introduced in July 1987[8], just before standard PS/2 SSKs were introduced. Despite all of this, the SSK never saw the same adoption as the Enhanced Keyboard had. It's believed that the importance of a dedicated numeric keypad during this period kept the full-size keyboard a more desirable option than the tenkeyless keyboard.

In 1990, IBM introduced the SSK for industrial computers starting with the IBM 7785 Service Bay System, a 386-powered cart-mounted computer based on the IBM Personal System/2 Model 80 for the automotive industry. It originally shipped with keyboard P/N 1395691[9]. In September 1992, IBMs 7537, 7546, and 7568 GEARBOX 800 also received industrial SSK keyboards as options[10]. The most famous industrial SSKs are P/Ns 1395682 and 41G3200 made for Mopar and Ford respectively. During the 1990s, IBM of course spun off its US-based keyboard manufacturing operations via the divesture of IBM Information Products Corporation forming Lexmark International, and with it saw IBM employ the SSK for increasingly more non-PS/2 or non-PS/2-based systems. According to PC Magazine in February 1992, the SSK was being used for IBM Personal System/1 lower-end computers[11]. By September 1992, the SSK was 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 (a Type IV 122-key Model M for terminal emulation)[12]. When the IBM PC 300 and 700 series were announced in October 1994, the SSK was made available as an option with box P/N 1396050 (containing a P/N 1392934 keyboard)[13][14]. After this though, the SSK along with Model Ms in general would be sidelined as IBM and the industry moved towards lower-cost keyboards.

Whilst many people believe the SSK died with IBM, that's in fact not exactly true. By 2002, successors to Lexmark's keyboard manufacturing operations, Unicomp, began selling P/N UNI04C6 as either the IBM or Unicomp 85 Key Space Saver. This very late SSK is also unique in that it has an ISO-based US English layout. Otherwise, it's a standard PS/2 SSK. Observed birth certificates of these keyboards can say it's a "Modification of IBM P/N 1394054", implying they're assembled from former IBM keyboards and parts rather than actual production. Unicomp stopped selling these when stock dried up sometime in the latter half of the 2000s. Since then, keyboard enthusiasts have continuously demanded a revival of the tenkeyless Model M from Unicomp. In the early 2010s, Unicomp confirmed they were working on such a replacement, which finally launched in 2021 in the form of the Unicomp Mini Model M.

Pricing

All inflation adjustments were made with US Inflation Calculator.

Date
Model
Original price
2021 price
1986-09-02
IBM 3162 terminal, P/N 1391518
$180[1]
~$369
1987-06-16
IBM 3151 terminal, P/N 1392980
$104[2]
~$248
1992-02-25
IBM PS/1
$156[11]
~$301
2002-10-14
Unicomp PS/2, P/N UNI04C6
$59[15]
~$89

Design

More information: Model M keyboards

Key-switches

More information: IBM buckling spring#Membrane

Animation of a buckling spring<a class='source-link' href='/wiki?id=modelmssk#Sources'><sup>[16]</sup></a>
Animation of a buckling spring[16]

Just like most Enhanced Keyboards, the SSK employs buckling spring over membrane switches. 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 membranes[17]. The mechanism rocks the membranes before its fully buckled (bottomed out), allowing for part-way actuation. Unlike the Enhanced Keyboard, the SSK appears to have not received a Quiet Touch rubber dome counterpart.

Outer case

The SSK is designed to heavily resemble the Enhanced Keyboard, so it uses the same colour palette and the same distinctive wedge shape case. This case shape facilitates a curved internal assembly that partially swoops up above the F-keys, granting space commonly used to hold items such as pens or pencils. Besides the lack of a numeric keypad and LED lock-lights, the main dimensional difference between the SSK and the Enhanced Keyboard is a shrinking of the aforementioned space above the F-keys. SSK cases are believed to be universally made with PVC, which means they typically don't yellow with UV exposure.

Internal assembly

The aforementioned curved assembly is comprised of three layers just like an Enhanced Keyboard; the barrel plate, the membranes and the backplate. The barrel plate sits top facing and is used to guide the individual switch components at their correct position above the membranes' 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 keyboards and terminal versions of both. The membranes are a part of the key-switch system used as the circuitry to be actuated by the buckling springs and facilitate a 16x8 matrix. The backplate provides rigidity. 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.

Internal assembly<a class='source-link' href='/wiki?id=modelmssk#Sources'><sup>[18]</sup></a>
Internal assembly[18]

Keycaps

SSK keycaps were of IBM's famed PBT dye-sublimated variety. Versus the most common keycap material, ABS[19], PBT is more durable, does not degrade/yellow with age, UV or heat exposure, and will keep its texture for longer without shining[20]. 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. Like Enhanced Keyboards, SSK keycaps were 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

Unlike Enhanced Keyboards, SSK controller PCB designs remained relatively similar throughout their production. IBM and later Lexmark stuck with 16+8 flex cable supporting controllers that early Enhanced Keyboards used, using TE Connectivity's 2.54mm pitched Triomate sockets for the membranes. SSKs also kept using modular shielded data link (SDL) based cables after it fell out of favour with Enhanced Keyboard production.

Speaker grille

SSKs possess the same speaker grille most Enhanced Keyboards have, however, SSKs with a speaker fitted have yet to be observed. On Enhanced Keyboards, the speaker was only fitted on keyboards destined to be used with RT PC and RS/6000 family computers and was used for providing a system audible queue. The lack of RT PC or RS/6000 SSKs explains why no SSK has been observed with one.

Flip-out feet

Branding

Since no first-generation SSKs made in 1986 (ie, from before Enhanced Keyboards received oval-shaped badges) have been observed in modern times, only oval-shaped IBM-branded SSKs are known albeit the oval itself is physically smaller than the ones Enhanced Keyboards sported. In line with their larger brethren, SSKs originally used an oval with grey text (1987-1992) and then an oval with blue text (1992-). A black oval was introduced in 1990 for the industrial version of the SSK.

Self-branded Lexmark SSKs featured a rectangle logo in the top-left corner. Whilst Unicomp marketed SSKs as late as 2007, the stock they sold either had IBM branding or no branding at all.

Layout

More information: IBM Model M Enhanced Keyboard#Layout

The SSK layout is a subset of the Enhanced layout, being basically the same except lacking a dedicated numeric keypad. The Enhanced layout is essentially the standard keyboard layout that most keyboards today still conform to with the addition of GUI keys and invariably altered modifier unit sizes.

Since numeric keypads were generally viewed favourably in the 1980s, IBM implemented a layer-based numeric keypad that overlays some of the alphanumeric keys. The numeric keypad can be activated by turning on the num lock, then the navigation commands on it can be used by shift-pressing the keys. Since its usual dedicated placement is gone, the num lock key is doubled up with the scroll lock key instead and is activated by shift-pressing the key. One consideration with this system is that due to the lack of lock-lights, a rogue num lock may cause frustration when entering passwords, especially if a preview option isn't available.

Connectivity

More information: Keyboard Connections topic

For the most part, the connectivity of SSKs aligns with that of the Enhanced Keyboard. PC compatible and industrial computer SSKs typically use a 6-pin modular AMP shielded data link (SDL) port and a high quality detachable coiled cable. This allowed the keyboard to be uncoupled from its cable as needed. Whilst SSKs were generally not intended for use with IBM PC/AT systems, SDL to 5-pin DIN cables Model Ms for those systems used could be coupled and used with SDL-based SSKs as well if desired.

Terminal variants have fixed cables with either 5-pin DIN connectors with a 240-degree PIN arrangement (IBM 3162 SSK) or modular 8P5C "RJ-45" jacks (IBM 3151 SSK). Terminal SSKs also generate IBM set 3 scancodes, contrasting the set 2 (aka, "AT") scancodes PC and industrial SSKs used.

Variations

DIN terminal Space Saving Keyboard (1986)

P/N 1391518

The first SSK was the so-called "shorter keyboard" option for the IBM 3162 ASCII Display Station, P/N 1391518. The keyboard was made available in October 1986, making it likely the only SSK made to first-generation specifications however no photos of this keyboard have been found. Despite the lack of photos, it can be assumed it connected via a 240-degree pin arranged DIN plug and spoke IBM scancode set 3 since Enhanced Keyboards for the 3162 (as well as the 3162 terminal itself) have been observed and they indeed have that plug.

8P5C terminal Space Saving Keyboard (1987)

P/N 1392980

The modular 8P5C connecting terminal SSKs are the earliest that can be properly described. Once again, only a sole part number (1392980) is known and it was intended for the IBM 3151 ASCII Display Station models 110 and 160. The keyboard was made available alongside the 3151 in June 1987, two months sooner than the first IBM Personal System/2 computer that came with an SSK. What's unusual about the 3151 SSK is that despite it being a terminal keyboard, it retains a modular cable via an SDL jack unlike any terminal version of the Enhanced Keyboard. P/N 1392980s seem to support scancode set 2 as well since examples sold with SDL to PS/2 cables have been observed[22].

Personal Typing System Keyboard (1987)

P/N 1392464

The IBM 6901 Personal Typing System (PTS) was a derivative of the IBM Personal System/2 Model 30 released in July 1987 intended specifically to be a word processing system similar to IBM's past Displaywriter systems. The PTS included many bundled features generally including a Wheelwriter-based printer (some models had Quietwriter-based printers) and IBM Displaywrite software that gives this Personal Typing System Keyboard (PTSK) its common nickname "Displaywrite keyboard". The PTSK sports numerous unique legends on its keycaps intended for its word processing purpose, many of which heavily resemble IBM Wheelwriter typewriter legends. The PTSK is also fairly unique in that it's an SSK with stepped modifier keys. Otherwise, the PTSK is essentially just a PS/2 SSK.

PS/2 Space Saving Keyboard (1987)

eg, P/Ns 1370475, 1391472, 1392934, 1393278

Just like the Enhanced Keyboard, PS/2 SSKs are the most common and well known. They were first available with the IBM Personal System/2 Model 25 models 001 and 004 from August 1987. They generally followed the Enhanced Keyboard in terms of updates, including the change from black text to blue text in the IBM oval badge and the addition of drainage channels for fluid spills. However, SSKs generally retained modular cables via SDL when most Enhanced Keyboards received fixed cables by the mid-1990s.

Airline reservation system PS/2 Space Saving Keyboard (1988)

P/N 1393691

The airline reservation system SSK is a PS/2 based variant and is another counterpart to a well known Enhanced Keyboard variant. Like the P/N 1393464 Enhanced Keyboard, it's typically referred to as a "Sabre" model due to IBM's historical ties with Sabre and the fact Sabre was a large customer of IBM PS/2 based systems. However, Sabre wasn't necessarily the only company to utilise these. 1393691 is the sole known part number and historical details and documentation are scarce. It also seems to be much less common than its Enhanced Keyboard counterpart, possibly due to the same reasoning that the loss of a dedicated numeric keypad would be viewed as significant during even the late 1980s.

Financial services PS/2 Space Saving Keyboard (1989)

P/N 1395217

The financial services SSK is another PS/2 based variant seemingly geared towards stockbrokers or financial services professionals. Interestingly, these lack a numeric keypad layer. The keyboard also sports a blue-legend Ctrl key, a dedicated Enter key in place of the right Ctrl (the typical Enter key is marked as a dedicated Return key instead), "Prev" and "Next" legends on the page up and page down keys respectively, "Quote" and "Select" keys in place of Scroll Lock and Pause respectively, IBM 3270-esque "PAx" keys on F1 through F3, "Reset", "Clear" and "Help" legends on F10 through F12 respectively, a back-tab legend on the pipe/forward slash key, and various green sublegends across the alphanumeric keys. 1395217 is the sole known part number and historical details and documentation are scarce.

Industrial Space Saving Keyboard (1990)

eg, P/Ns 1395691, 1395682, 41G3200

The Industrial SSKs are a cosmetic variation of the standard PS/2, characteristically sporting grey-coloured casing designed to hide the dirt and damage expected to be inflicted upon the device within an industrial environment. Industrial SSKs were heavily associated with the automotive industry, with P/N 1395682 and P/N 41G3200 specifically known to be used with Mopar and Ford owned systems respectively. The "Mopar" version is also iconic for its blue-coloured keys on F1, F2, the navigation cluster and arrow keys.

Lexmark Spacesaver Keyboard (1992)

P/N 1397961

The Lexmark Spacesaver Keyboard is Lexmark's own-branded counterpart to the IBM PS/2 SSK. Besides having the unique rectangular Lexmark branding, it's otherwise an ordinary SSK.

Unicomp 85 Key Space Saver (2002)

P/N UNI04C6

These were the very final SSKs released although they are not newly manufactured keyboards. Most P/N UNI04C6s will say "Modification of IBM P/N 1394054" on their birth certificates to highlight the fact they're made from modified older stock and/or using leftover parts from the IBM and Lexmark era. They're PS/2 SSKs notable for having a US English ISO layout with overlay numeric keypad legends that are a lighter shade of blue than IBM or Lexmark era SSKs. Unicomp stopped selling these when stock dried up.

Successor

Indirect successors

Technically speaking, the two successive successors to the Space Saving Keyboard in IBM's eyes had been introduced whilst the SSK proper was still in production. In 1992, IBM and Lexmark developed the Models M4 (non-TrackPoint) and M4-1 (TrackPoint) Space Saver buckling rubber sleeve keyboards for the IBM Personal System/2 E and various ThinkPads (intended for their docking solutions), made available as an option for various IBM systems via the Select-A-Keyboard scheme. Model M4s were referred to as 84/85 key "IBM Quiet Touch Keyboards" as well. The Model M4s are best described as indirect successors since they were IBM's primary tenkeyless keyboards for most of the 1990s, but they did not outright replace the SSK on all fronts. The Space Saver Keyboard was then followed by the NMB-made IBM Space Saver II (model RT3200) introduced in 1999. The name of the RT3200 clearly defines it as the successor of the Model M4s, but Space Saver IIs found themselves with relatively less adoption beyond server console usage. The RT3200 also abandons any Model M family technology, instead using rubber dome key-switches.

Spiritual successor

Ever since the discontinuation of the SSK, Unicomp had continuously faced calls to reproduce or redevelop a tenkeyless Model M. For almost the entire 2010s, it was known Unicomp was low-key developing such a keyboard but details on progress were scarce. Prior to 2019, the only glimpse of such a new Unicomp keyboard was their 2014 April Fool's Day concept illustration that portrayed a radical departure from a typical Model M design[28]. However, the first photo of a real Unicomp SSK successor appeared on 16th September 2019 that showed a generally more classic design featuring the typical SSK shape and layout but with added GUI keys[29]. On 20th December 2019, it was officially announced as the Unicomp Tenkeyless and slated for an end of 2020 Q1 availability[30]. However, due to the effects of the subsequent COVID-19 pandemic, the launch was pushed back several times. The keyboard finally went on sale on 24th February 2021 and started shipping on 20th March 2021, now called the Unicomp Mini Model M[31]. In addition to the inclusion of GUI keys, the keyboard also sports LED lock-lights, a detachable double-ended USB Type-A cable, and an upgraded membrane and matrix design.

Sources

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

  1. 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 [accessed 2022-03-04].
  2. IBM - IBM 3151 ASCII Display Station Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  3. IBM - IBM 8525, Personal System/2 Model 25 Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  4. IBM - IBM Personal System/2 Model 40 SX (8540-040, 043, 045) Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  5. IBM - IBM Personal System/2 Model 35 LS (8535-14X) Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  6. IBM - IBM PS/2 Model 57 SLC Brief Description of Announcement, Charges, and Availability [accessed 2022-03-04].
  7. IBM - IBM Personal System/2 Model 95 XP 486 (9595-0LF, 0MF and 0MT) Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  8. Wikipedia - List of IBM PS/2 models [accessed 2022-03-16].
  9. Ardent Tool - IBM 7785 Hardware Maintenance Reference/Service [accessed 2022-03-27].
  10. IBM - IBM Industrial Computer Feature Enhancements and Additions Announcement Letter [accessed 2022-03-04].
  11. PC Mag - 1992-02-25 [accessed 2022-02-27].
  12. IBM - IBM PS/2 76 486, 77 486, 77 486DX2; Ultimedia M77 486 and Ultimedia M77 486DX2; and PS/2 486-33/66 Microprocessor Upgrade Option Brief Description of Announcement, Charges, and Availability [accessed 2022-02-27].
  13. IBM - IBM PC 300 Series Pentium Systems Announcement Letter [accessed 2022-02-27].
  14. IBM - IBM PC 700 Series -- Pentium/ISA Systems Announcement Letter [accessed 2022-02-27].
  15. Unicomp - IBM, Lexmark and Unicomp Keyboard Specials [accessed 2022-02-27].
  16. Shaddim - File:Bucklingspring-animation-300ms.gif [accessed 2021-09-09]. License: CC-BY-2.0.
  17. IBM - Rocking switch actuator for a low force membrane contact switch [accessed 2021-06-17].
  18. Blake Patterson - File:Blake Patterson IBM Model M Keyboard space saver open back.jpg [accessed 2021-09-09]. License: CC-BY-2.0 (cropped & perspective corrected).
  19. WASD Keyboards - Mechanical Keyboard Guide [accessed 2021-09-09].
  20. Switch And Click - ABS vs PBT Keycaps: What’s the Difference? [accessed 2021-09-09].
  21. Joe/Ellipse @ modelfkeyboards.com - Converted RJ-45 Terminal IBM Model M SSK 1392980 [accessed 2022-03-16]. License: permission requested and explicitly given via direct correspondence.
  22. ClickyKeyboards.com - IBM model M 84-key (space saving SSK) 1392980 10-09-91 [accessed 2022-04-04].
  23. P. Zwettler - IBM Model M SSK 1392464 DisplayWrite [accessed 2022-02-27]. License: All Rites Reversed.
  24. P. Zwettler - IBM Model M SSK 1395217 [accessed 2022-02-27]. License: All Rites Reversed.
  25. P. Zwettler - IBM Model M industrial SSK 1395682 [accessed 2022-02-27]. License: All Rites Reversed.
  26. elecplus - A Comparison of SSKs [accessed 2022-04-10]. License: permission requested and explicitly given via direct correspondence.
  27. Tsuyoshi Ide @ ide-research.net - UNI04C6 [accessed 2022-03-26]. License: permission requested and explicitly given via direct correspondence.
  28. Unicomp - 2014-04-01 Facebook Post [accessed 2022-03-05].
  29. Unicomp - 2019-09-19 Facebook Post [accessed 2022-03-05].
  30. Unicomp - 2019-12-20 Facebook Post [accessed 2022-03-05].
  31. Unicomp - 2021-02-24 Facebook Post [accessed 2022-03-05].