Model M keyboard

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Model M
IBM Model M.png
The first IBM Model M. This particular unit manufactured in 1986.
Part number Various
Branding IBM, Lexmark, Unicomp, others
Manufacturer IBM, Lexmark, Maxi Switch, Unicomp
Product family IBM Model M
Layouts 101/102/104 ANSI, 102/103/105 ISO
Keyswitches Buckling-spring, Dome-switch keyboard
Interface PS/2, AT, Terminal
Weight 2.0–2.5 kg
Introduced 1985
The characteristic sound produced by the buckling-spring mechanisms of a Model M keyboard.

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Unicomp Model M with removed z key. Exposing the buckling spring.

Model M is a designation for a group of computer keyboards manufactured by IBM starting in 1984, and later Lexmark, Unicomp and MaxiSwitch. The many variations of the keyboard have their own distinct characteristics, with the vast majority having a buckling-spring key design and swappable keycaps. Model M keyboards have been praised by computer enthusiasts and frequent typists due to their durability and consistency, and the tactile and auditory feedback they provide while typing.

The Model M is also regarded as a timeless and durable piece of hardware.[1][2][3][4] Although the computers and computer peripherals produced concurrently with the Model M are considered obsolete, many Model M keyboards are still in use, due to their physical durability and the continued validity of their ANSI 101-key layouts. Recently, these keyboards have made a comeback among writers and computer technicians.[5] The Kentucky-based company Unicomp continues to manufacture and sell Model M-style keyboards.[5]


Keycap in a French Model M

The Model M was designed to be a more cost effective keyboard than the Model F keyboards it replaced. Production for the original Model M began in 1985, and the keyboards were often bundled with new IBM computers in the 1980s. These keyboards were produced by IBM in their plants in Lexington, Greenock and Guadalajara. The most common Model M variant is the part number 1391401, which was the US English layout keyboard of the IBM PS/2. Until 1987, the keyboards featured a detachable AT cable; after that, they were bundled with a detachable PS/2 cable. Cables came in both 5- and 10-foot lengths (1.5 and 3 metres). From about 1994 onwards, the majority of Model Ms were manufactured with non-detachable cables to cut down manufacturing costs; however, they retained the 101-key layout, never implementing the Microsoft Windows keys. Unicomp later designed a 104-key Model M including those keys.

On March 27, 1991, IBM divested a number of its hardware manufacturing operations, including keyboard manufacturing, to the investment firm Clayton & Dubilier, Inc. in a leveraged buyout to form Lexmark International Group, Inc.[6][7][8] Lexmark continued manufacturing the Model M keyboard in the United States, United Kingdom, and Mexico with IBM being Lexmark's major customer.[9] Many of the keyboards had IBM assembly part numbers 52G9658, 52G9700, 82G2383, 42H1292, and others. Because of pricing pressures, many of these Model M keyboards were manufactured with a new lower-cost design[10] including lighter-weight plastic, integrated cable, and uniform print color on the keys.

On March 27, 1996, Lexmark's contract to produce keyboards for IBM expired, and Lexmark transitioned its keyboard business to IBM and other vendors.[11] Some of the manufacturing assets were sold to a group of Lexmark employees, who formed Unicomp. The Model M keyboard, similar to part number 42H1292 but first renamed 42H1292U and subsequently the "Customizer", is still in production. A variety of configurations are available from Unicomp, including updated 104- and 105-key layouts; a Linux layout (where the Ctrl and Caps Lock keys and Esc and tilde keys are swapped); models with integrated TrackPoint pointing sticks or integrated trackballs; and POS-specific models, such as those with built-in magstripe readers. When Lexmark discontinued production in March of 1996, IBM continued production in Greenock, Scotland and subcontracted production of the Model M13 keyboard (IBM Enhanced Keyboard with TrackPoint II) to Maxi Switch in Mexico. Production of Model M keyboards by these companies ended in 1999 and 1998 respectively. Although current Unicomp models may still be purchased, original production models retain their value well among collectors and computer enthusiasts.[citation needed]


Numerous variations of the Model M incorporated alternative features and also colours. One of the most popular variants is the "Space Saving Keyboard" which integrates the number pad into the keyboard's main section, substantially reducing its width. IBM released the regular Model M and Space Saving Keyboard Model M in an alternative 'gray/pebble' colour for use with their Industrial computers. Other differences included a grounded spacebar and (sometimes on later models) drainage holes to accommodate harsh environments.


Buckling spring key on key press and release. U.S. Patent 4,118,611, issued to IBM in 1978
Graph of key force over key travel for a buckling spring key. Visible in graph position 1C the fast force drop when the spring buckles. U.S. Patent 4,118,611, issued to IBM in 1978

The model people commonly refer to when they mention "Model M" is Part No. 1391401, which was by far the most common. This enhanced keyboard model included the patented buckling spring design[12] and swappable keycaps, as well as the heavy and sturdy design of the Model Ms in general. This keyboard is widely praised as being well-built. Evidence of this can be seen in the fact that keyboard design has changed little in the past twenty years, while the designs of everything from PCs to monitors to mice have changed dramatically.[original research?] The sturdy design (including heavy steel backplates and a strong plastic frame) of the keyboard allows even the most abused to survive for years. The keyboard's variations (referred to by Part Number, printed on each keyboard's back label) have small differences, while keeping the robust and distinctive key mechanism that makes the boards unique. For example, the 1391472 variant does not have a separate number pad, but it incorporates it into the main key area, as many laptop keyboards do; and the early 1390120 has no LED "lock lights" to indicate the status of the Num Lock, Scroll Lock, and Caps Lock keys.

The Model M's buckling spring key design gives it a unique feel and sound. Unlike more common and cheaper dome switch design, the Model M’s buckling springs give users unmistakable tactile and auditory feedback. Some users report that they can type faster and more accurately on the Model M than on other keyboards.[13][14]

The Model M is also less susceptible to dirt and wear and tear. While dirt will interfere with proper operation of a dome switch keyboard, the design of a buckling spring keyboard is such that any dirt that falls between the keys is unlikely to enter the switch mechanisms, which are covered by the keys. Even if dirt were to enter a mechanism, a large amount would be necessary to prevent it from operating.[citation needed]

Most Model M's, up until the late 4th-generation variants, have a 1.25" slotted, circular speaker grille molded into their bottom surfaces. Relatively few contain an actual speaker, however, as it was useful only for sounding beep codes on older terminal systems. (The most common Model M variant with a speaker is the 1394540, made for RS/6000 UNIX workstations.)

There are some drawbacks to the Model M design:

  • Because they are so large and heavy (over 3 lbs, heavier than some modern laptops) they are not as portable as more modern keyboards.
  • Their buckling-spring keys are noisy enough to be inappropriate in quiet locations such as libraries and offices.
  • Liquids spilled on most Model M's do not drain out, and remain in the keyboard with potential to cause a short circuit. The later 42H1292 and 59G780 designs, as well as post-1993 1370477s and 1391401s, made mostly by Lexmark and Unicomp, include drainage channels designed to avoid this problem.
  • Unicomp currently produces Model M's with USB connectors that can be used directly with modern PCs. However, earlier Model M's have either AT or PS/2 connectors, requiring adapters for use with PCs lacking those capabilities (PS/2-to-USB adapters exist for computers without PS/2 ports; and additional AT-to-PS/2 adapters, or SDL-to-PS/2 cables, for computers without AT ports). Some PS/2-to-USB adapters are unreliable with early Model M's that require more power than the adapters can provide.[15]


The square aluminium badge on a 1390131 series keyboard compared to other variants.

All Model M keyboards manufactured by either IBM or Lexmark feature an ID label on the underside indicating the assembly part number, individual serial number, and date the keyboard was manufactured. There are other more obvious ways to distinguish between the range, namely the type of badge featured on the top of the keyboard. The first model Ms (part numbers 1390120 or 1390131) featured a square aluminum IBM badge in the top right corner. Part number 1391401 featured an oval, white IBM logo with grey lettering in the top left of the board. The later IBM manufactured keyboards and subsequent Lexmark keyboards of the early 1990s (IBM assembly part numbers 1370477, 52G9658, 52G9700, 59G7980, 92G7453, 82G2383, 42H1292, and others) featured a similar oval badge to part number 1391401, but instead with a grey background and blue lettering.

Features by part number[edit]

Note: The manufacture dates are approximate. Click "Show" to display the uncollapsed table.


See also[edit]


  1. ^ King of click: the story of the greatest keyboard ever made
  2. ^ "The Best Keyboard You've Ever Typed On". Life hacker. Retrieved 2013-12-01. 
  3. ^ "Inside the World's Greatest Keyboard". PC World. Retrieved 2013-12-01. 
  4. ^ "The world's best keyboard, and why it's so great". UK: PC advisor. Retrieved 2013-12-01. 
  5. ^ a b Kaste, Martin (January 30, 2009), Old-School Keyboard Makes Comeback of Sorts, National Public Radio .
  6. ^ "Customs Ruling HQ 544887". U.S. Customs and Border Protection. October 2, 1992. 
  7. ^ "IBM Archives: 1990s". IBM. 
  8. ^ Lewis, Peter H. (December 22, 1991). "The Executive Computer; Can IBM Learn From a Unit It Freed?". The New York Times. 
  9. ^ Levine, Bernard (1991). "Keyboard vendors punched on prices". Electronic News. 
  10. ^ "Lexmark International Reports Best Year Ever Since Independent of IBM". Business Wire. December 12, 1994. 
  11. ^ "Lexmark International Group 1996 annual report, SEC Form 10-K". Advameg. March 24, 1997. 
  12. ^ US patent 4118611, Richard Hunter Harris, "Buckling Spring Torsional Snap Actuator", issued 1978-10-03  — an IBM patent for buckling spring keys.
  13. ^ Doug Reilly (May 4, 2005), "My Clickety IBM Keyboard – RIP", blogs (Microsoft), archived from the original on 2006-02-17 
  14. ^ Cramer, Ryan, "The IBM Model-M Keyboard", Timeless Tools, RCD 
  15. ^

External links[edit]