Model M3 L40 SX Keyboard Assembly & Numeric Keypad

Also partially applies to SAIC Galaxy 1100 Keyboard Assembly

The IBM 8543 Personal Computer/2 Model L40 SX was an early notebook-style 386SX laptop announced in March 1991 and is amongst the more famous of the IBM ThinkPad's predecessors. Whilst the L40 SX itself was not notably successful and its development was famously rushed, its keyboard received widespread praise in the press. The IBM Personal System/2 L40 SX Keyboard Assembly and IBM Numeric Keypad for IBM Personal System/2 L40 SX are members of the Model M keyboard family, designated "Model M3". Developed at IBM Lexington, the M3 represented a major turning point in the Model M's history, introducing the IBM buckling sleeve tactile keyswitch and was the genesis of a new, diverged Model M lineage using it. The L40 SX and the M3 only lasted fifteen months on the market, but its legacy reaches far. It was directly derived to become the IBM Space Saver Keyboard and Numeric Keypad family (Models M4 and M4-1), and evolved into the original IBM ThinkPad Keyboard family (Models M6 and M6-1) that went on to build the ThinkPad's reputation for having high-quality and durable keyboards. It was also borrowed for the SAIC Galaxy 1100 portable HP-UX workstation.

Contents

Summary

History

Development for the IBM Personal System/2 Model L40 SX (type 8543) began in February 1990 under the purview of IBM United States Boca Raton, Florida, the location of IBM Entry Systems Division. Harvard University expressed interest in an IBM notebook and planned to be a major customer for L40 SX^[11][11]
Laptop Retrospective - Think Design Stories: IBM PS/2 L40 SX Story (ft. Tom Hardy) [accessed 2025-02-16].. From the onset, the effort was to stray from IBM's typical two-year lead time for developing a personal computer from start to finish as IBM had assessed that it was already late with introducing an Intel 80386SX based notebook computer^[9][9]
Computerworld - 1 April 1991 [accessed 2025-02-16].. IBM Information Products Division (predecessor to Lexmark International) under CEO Tony Hancock was responsible for the laptop's cover set and keyboard design, which was completed by IBM United States Lexington, Kentucky (plant code 11). The completed designs were then given to Leap Technologies of Otsego, Michigan to produce moulds for, skipping possible mock-up and prototype stages^[9][9]
Computerworld - 1 April 1991 [accessed 2025-02-16].. These efficiencies reduced the IBM Model M3 keyboard assembly and IBM buckling sleeve keyswitch development time to just 5 months. Assembly and final production would fall to IBM United States Raleigh, North Carolina (plant code 23) and IBM United Kingdom Greenock, Scotland (plant code 55).

Most of the L40 SX's design was done outside IBM's typical design review processes, and it was only critiqued late into its development. IBM designers Tom Hardy and Richard Sapper were particularly critical of its design. For example, it sported a side-mounted floppy drive when the laptop's lid originally hung over the base unit's sides and could break a partially inserted/ejected floppy diskette, requiring notches to be cut out to avoid this issue. The L40 SX's design team also wanted to make it black, but this suggestion was denied because IBM was planning to launch the ThinkPad as IBM's main black portable computer the following year. Former IBM Vice President of Marketing Leo Suarez claimed in the book "ThinkPad: A Different Shade of Blue" that the L40 SX not being black was due to IBM executives believing it would be "out of character for the personal computer market", but Hardy refuted this in writing in the same book^[11][11]
Laptop Retrospective - Think Design Stories: IBM PS/2 L40 SX Story (ft. Tom Hardy) [accessed 2025-02-16].. Despite this, IBM would later introduce the PS/2 CL57 SX, PS/2 Note, PS/55note and PS/note series with black cover sets in the interim between L40 SX and ThinkPad. Ornamental design patent applications for the L40 SX numeric keypad and laptop cover set were filed on 5^th November 1990^[12][12]
IBM - Auxiliary keypad [accessed 2025-02-16]. License/note: provided by Google Patents. and 25^th January 1991^[13][13]
Lenovo - Portable computer housing [accessed 2025-02-16]. License/note: provided by Google Patents. respectively.

The L40 SX model A44 (EMEA model series) was announced first on 13^th March 1991^[2][2]
IBM - The IBM PS/2 Model L40 SX system (8543-A44) and Features (#ZG91-0105) [accessed 2025-02-16].. This was followed by model 044 (USA) announcement and release on 26^th March 1991, 13 months after its development began and with a launch price of $5,995 USD^[3][3]
IBM - The IBM PS/2 Model L40 SX System and Features (#191-030) [accessed 2025-02-16].. It received a mixed overall reception from the press, but was widely praised for its keyboard. In April 1991, Computerworld noted that its price tag "may hinder acceptance in the less IBM-loyal mass market" and that there were several competitors that were smaller, lighter and two-thirds the price whilst still using an Intel 80386SX CPU. However, they noted that analysts and users praised its keyboard, with one saying "it's got the best keyboard of any [laptop] by far". In May 1991, PC Mag called it a "potentially fine laptop" with its primary strengths being its keyboard, possible features and options, but disliking its LCD quality and inferior memory benchmark results compared to a contemporary Compaq competitor^[14][14]
PC Mag - May 14, 1991 [accessed 2025-02-16].. Later in August 1991, PC Mag ran a new article about the L40 SX, noting that it was much larger than other notebooks of the time and should be considered more of a desktop replacement rather than a true laptop, and that the primary attraction was its "spacious" and "amazing" keyboard^[10][10]
PC Mag - August 1991 [accessed 2025-02-16]. License/note: photos used under fair dealing..

L40 SX model 044 was withdrawn from marketing on 9th July 1992^[4][4]
IBM - Withdrawal: IBM PS/2 Model L40SX (8543-044) (#192-161) [accessed 2025-02-16].. Production of the L40 SX numeric keypad continued into at least March 1993^[5][5]
ASK Keyboard Archive Photos - P/N 1396199 (1993, IBM-US) [accessed 2025-02-18]. License/note: saved from volatile eBay listing & used under fair dealing.. In May 1993, IBM voluntarily recalled the L40 SX worldwide after receiving 15 complaints of a short circuit, repairing any units returned for free^[15][15]
InfoWorld - May 31, 1993 [accessed 2025-02-16]..

Design

Keyswitches

More information: IBM buckling sleeve

The Model M3 keyboard assembly and numeric keypad were the first hosts for IBM buckling sleeve keyswitches. Provisionally known in full as IBM Quiet Touch buckling rubber sleeves, they were IBM's primary portable computer keyswitch technology between 1991 and 1996 and found their way onto most IBM and later Toshiba Global Commerce Solutions point-of-sale keyboards from 1993 to present day. Unlike generic rubber dome keyswitches, the rubber component in IBM buckling sleeves plays no part in pressing down on the keyboard's membrane assembly. Instead, the design offloads this duty to rods on the keycaps or barrel-mounted sliders (depending on specific model/variant) that descend through the keyboard's keyswitch barrels. This effectively eliminates the mushy feeling of bottoming out on rubber dome keyboards since the actuation interface is more solid, whilst still keeping the design tactile and relatively quiet. IBM buckling sleeves are very snappy and quite tactile, with what is perhaps best described as a medium stiffness feel relative to other keyswitch designs.

Model M3 was not only is the genesis of the IBM buckling sleeve itself, they started a lineage known as M3/M4/M4-1 type IBM buckling sleeves. As the name implies, the subsequent Model M4 and M4-1 keyboards and numeric keypads use the same design. The design is also known as being "rod actuated" as a fixed plunger on each keycap is what descends through the keyswitch barrels to actuate the membrane assembly underneath, giving a firm and solid bottom-out feel.

Cover set

The M3 keyboard alone does not have a cover set, it is a sub-assembly that sits inside a given L40 SX notebook. Typical for laptops of this era, it has no surrounding palm rest and the keyboard becomes the entire front half surface when fitted. The L40 SX's cover material is a polycarbonate and acrylonitrile butadiene styrene (PC + ABS) plastic blend.

Being a complete device, the M3 keypad does has a cover set and is also made of PC + ABS plastic. The top cover piece is hinged and lifts to reveal the keys but can also be removed if desired. The bottom cover piece (P/N 1396159) holds everything else. The overall style and the folding top cover has resulted in comparisons with cigar boxes being drawn.

The M3 keyboard has three brass-socketed screws holding it to the L40 SX. The M3 keypad has four screws hiding under each rubber feet. For both designs, the plastic surrounding screws/screw sockets has been known to break with age. It's possible to glue them back into place if needed.

Assembly

The M3 keyboard and numeric keypad complete sub-assemblies somewhat resemble that of their larger, more familiar brethren. The assemblies comprise four layers; the keyboard frame, the membrane blanket, the membrane assembly and the base plate. However, the keyboards and keypads differ in how the keyboard assembly is held together.

Keyboard assembly hooks & opening

The keyboard assemblies have base plates that sport many hooks that go through the membrane assembly and blanket to grab onto the keyboard frame. Towards the centre, a sloped plastic part is visible that serves as a point of release for when one wants to remove the base plate and frame from each other. The release may have some sticky transparent plastic covering it. As such (and along with Model M4, M4-1, M6 and M6-1 keyboard assemblies), Model M3 keyboard assemblies can be non-destructively opened whereas most larger Model M variants cannot.

If one wishes to open the keyboard assembly, the release can be pushed whilst gentle pressure is used to slide and detach the base plate - if you orientate the keyboard on a flat surface where the edge with the three screws is closest to you, the base plate should slide to the right.

Keypad assembly rivets

The keypad assemblies are held together by six plastic rivets designed to provide the tension needed for the keyswitches to operate properly. Unfortunately, these rivets are the single largest flaw in the typical Model M design as they can weaken and break with age. Whilst the procedure has not been performed and documented on an M3 numeric keypad yet, such an issue may be permanently solved with a bolt or screw mod much like the mods performed on larger Model M variants.

Keycaps

Model M3 have dye-sublimated PBT keycaps with a pearl and pebble colour scheme. Versus the most common keycap material, ABS^[19][19]
WASD Keyboards - Mechanical Keyboard Guide [accessed 2022-07-01]., PBT is more durable, does not degrade/yellow with age, UV or heat exposure, and will keep its texture for longer without shining^[20][20]
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, silk-screening, laser etching or laser etching with infill.

Each keycap has two clips on opposite edges of the keycap to retain it in place and prevent it from significantly rotating in its place. Any keycap larger than 1 unit additionally receives a metal wire stabiliser. The M3 keycap mount was inherited by Models M4 and M4-1 and thus are compatible with each other's keycaps, but no subsequent IBM buckling sleeve implementation used this mount.

Controller card

Keyboard

The M3 keyboard controller is integrated onto the L40 SX's motherboard. It is an PLCC-package Intel 8042AH 8-bit microcontroller that could be labelled either "U73" or "U75" on the motherboard PCB^[21][21]
Ardent Tool - 8543 Planar [accessed 2025-02-20].. The keyboard's membrane assembly is socketed via connectors "J18" (8-pin) and "J19" (19-pin), which are TE Connectivity 2.54mm pitch Triomate family sockets.

Keypad

The M3 keypad has its own discrete controller card sporting a PLCC-package Intel 80C51BH 8-bit microcontroller (P/N 1397173). The card may have part numbers 1397174 (front white label) and 1396188 (rear copper fill) on it. The keypad's membrane assembly is socketed via connectors "J3" (5-pin) and "J4" (4-pin), which are also TE Connectivity 2.54mm pitch Triomate family sockets. Much like other contemporary Model Ms such as IBM Selectric Touch Keyboards (Models M1 and M2), the M3 keypad's surface-mount capacitors are a potential failure point. If the keypad does not work after a long period of disuse, the capacitors may need to be replaced.

Branding

The M3 keyboard itself has no branding, but the L40 SX notebook has two silver on pebble (grey) oval badges with "IBM PS/2 Model L40 SX" written on them on top of the lid and besides the screen. The M3 keypad's removable top cover piece has its own silver on pebble oval badge with just "IBM" written on it.

Rear labels

M3 keyboards made by IBM United States may have two rear labels. The one that should always be present is the one with a barcode, the main part number and a month-year date code. The secondary one will have a precise month-day-year date code and fields pertaining to a quality control process, with all values handwritten. Only one style of IBM U.S. M3 keypad rear label has been observed, and it is notably the only one that explicitly states "Model M3".

M3 keyboards and keypads made by IBM United Kingdom share one style of rear label, containing typed general data and handwritten quality control signatures, a year-month-day date code, and most notably a FRU number when IBM U.S. M3 rear labels almost always lacks one.

Layout

Marketing surrounding the L40 SX makes reference to the notebook having a keyboard that is as close to a desktop-sized keyboard as possible, including retaining 19mm key spacing, but some compromises were still needed to ensure the notebook was not too wide. The M3 keyboard introduced a unique semi-compacted tenkeyless layout, and the optional numeric keypad and its standard 17-key PC-style layout allowed for a full 101/102-key experience if desired. The keyboard layout's typewriter section was generally preserved relative to the Enhanced layout, though 0.5 units was removed from all of its right-most keys. For ISO layout keyboards, the key bottom-left to the Enter key was slightly reduced in size to maintain as much thickness to said Enter key as possible. All keys outside this section take on a more square-like appearance and are approximately 0.9 units in size. The navigation block is now 2x3 instead of 3x2 and the arrow keys are moved closer to the typewriter section, resulting in the right shift key, right Ctrl and right Alt/Alt Gr keys being smaller and the latter two moved closer together.

The left Ctrl and Alt keys were also reduced to 1 unit and spaced further apart. It is unknown why this is the case for L40 SX, but it may be theorised this was intended for a planned but cut integrated pointing device as later Model M6-based Lexmark AR10 and GS20 keyboard assemblies put mouse keys in this area. The M3 keyboard layout was inherited by Models M4 and M4-1 keyboards and Type 1 Model M6 keyboard assemblies. Type 2 Models M6 and M6-1 such as the aforementioned AR10 and GS20 would also remain based on M3, though rearranging the layout to resemble something closer to the classic ThinkPad layout. The M3 layout has also been suggested as possible inspiration for the modern 71-key layout^[23][23]
No Thoccs Aloud - Review Series: The 71-Keys Rabbit Hole [accessed 2025-02-22]..

Accessories

Keyboard templates

A possible publication that was available for the L40 SX was the Keyboard 3-Template Set (P/N 84F9782, document no. S84F-9782), costing $168.00 USD at launch^[3][3]
IBM - The IBM PS/2 Model L40 SX System and Features (#191-030) [accessed 2025-02-16].. These templates sat above the keyboard and provided spaces for the user to annotate key combinations or any program-specific functions they wish to remember. A scan of this template can be found on Michael B. Brutman's website.

Connectivity

Keyboard

The M3 keyboard does not have any 'intelligent' connectivity itself as its controller is integrated onto the L40 SX's motherboard.

Keypad

At its rear, the M3 keypad has a modular 8P7C port for a removable keypad-to-laptop cable and a 6-pin Mini-DIN port to pass through a PS/2 mouse. The removable cable is grey, lacks coiling and is relatively short. The PS/2-like plug at the end of the cable is unique to IBM portables, designed to carry both keypad and mouse signals through a single plug.

The laptop's PS/2 port was designed in such a way that it could natively accept any PS/2 mouse, so its pinout was designed accordingly. Likely, it was envisioned that users were far more likely to hook up a mouse rather than an external keyboard. The keypad's DATA and CLOCK lines are connected through the two pins usually redundant on single-purpose PS/2 plugs and sockets. The keypad still uses IBM Mode 2 protocol and set 2 scancodes though, so it can be made to work through a regular PS/2 port via a custom removable cable or a custom passive adapter, or one can use the modular port to attach a custom active PS/2 to USB converter.

Configuration

Windows 3.0 setup on L40 SX

If one tries to install Windows 3.0 on an L40 SX without the numeric keypad attached, the SETUP program will detect the keyboard as "All AT type Keyboards (84 - 86 keys)", which may prevent some functions working. To correctly configure the keyboard, one will have to manually select the "Enhanced 101 or 102 key US and Non US keyboards" option or (if available) connect the L40 SX numeric keypad before powering on the L40 SX and running the SETUP program.

During the Windows installation, one will also need to alter CONFIG.SYS to ensure the keyboard is not locked out by the HIMEM.SYS driver. This change can be made once the SETUP program finishes copying files to the system.

Enable keyboard clicking on L40 SX

The L40 SX can be made to produce a clicking sound through its speaker on each key press. This makes M3 in fact one of the few post Model B and Model F era IBM keyboards that have or at least can emulate a clicker assembly. To enable this, the PS2.EXE utility from the L40 SX reference diskette is needed. A copy can be obtained from the Ardent Tool. The following relevant commands can be used with this tool:

SAIC Galaxy 1100

The only other known portable computer to use an M3 keyboard assembly is the SAIC Galaxy 1100. The 1100 was introduced in 1994^[6][6]
OpenPA - SAIC Galaxy 1100 [accessed 2025-02-21]. and was a portable HP-UX workstation designed for military and intelligence usage^[26][26]
Old Vintage Computing Research - SAIC Galaxy 1100: a pre-CDE VUE of the PA-RISC with a security clearance [accessed 2025-02-20]. License/note: CC BY-NC-ND 4.0.. It used a 60MHz or 80MHz PA-RISC-based HP PA-7100LC processor, could have between 32 and 128MB RAM, had an active-matrix 1024x768 colour display, and was built to several military standards. It was in production as late as November 1996^[7][7]
SAIC - Galaxy 1100 [accessed 2025-02-21]. License/note: retrieved via Wayback Machine (1996-11-15 capture)..

The 1100 keyboard assembly only differs by its ThinkPad-style overlay numeric keypad (though its legends are red, whereas ThinkPads used typically blue, grey or white legends) and the lack of holes towards the bottom lip for the L40 SX's screen latches. Considering the latter, the assembly design is of the revised version for M4, but this is still considered M3 since it is still mounted in a portable computer instead of being a discrete keyboard. The 1100 was introduced after IBM United States had stopped producing buckling-sleeve Model Ms in general and IBM United Kingdom was only making Model M6/M6-1 as part of their buckling-sleeve Model M quota by 1994, thus Lexmark is the most likely OEM candidate as they were producing M4s during most of the 1100's lifetime. However, the 1100 was still in production after Lexmark exited the keyboard market in April 1996, so it's unclear if SAIC stockpiled pre-made keyboards or if Key Tronic or Unicomp (who produced M3/M4 style keyboards after Lexmark) made them.

"Model M3" IBM 3153 keyboard

There is another IBM keyboard that has been spotted with an "M3" designation, P/N 25H2142 IBM 3153 InfoWindow II Color ASCII Display Station Keyboard. This keyboard is based on the buckling-spring IBM Selectric Touch Keyboard (Models M1 and M2) design rather than the buckling-sleeve M3s from L40 SX. It is presently believed this is either an oversight or a misprint as this keyboard appeared by March 1995^[27][27]
IBM - IBM InfoWindow II 3153 ASCII Display Station Announcement Letter (#195-099) [accessed 2025-02-22]., 4 years after L40 SX was introduced, and does not appear to be unique to existing M2s.

Gallery

L40 SX

L40 SX interactive demonstration

Part number list

32 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.

Directory entries

3 keyboards have been found in the ASK Keyboard Directory.

Further reading & resources

Internal

External

Sources

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

ASK-M. Admiral Shark's Keyboards original measurement. Assume ± 1mm (length) or ± 10g (mass) accuracy.

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