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.

The Model M keyboard is a designation for a group of computer keyboards manufactured by IBM starting in 1984, and later Lexmark, Unicomp and MaxiSwitch. The many different variations of the keyboard have their own distinct characteristics, with the vast majority having a buckling-spring key design and many having fully swappable keycaps. Model M keyboards have been praised by computer enthusiasts and heavy typists because of the tactile and auditory feedback resulting from a keystroke.

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. Unicomp, which now owns the rights to the product's design, continues to manufacture and sell Model M-style keyboards.[citation needed] Recently, the keyboards have made a comeback among writers and computer technicians.[5] Unicomp has had difficulty making them profitable because they rarely break, many of the original IBM units are still in service showing no signs of wear and most retailers will not stock such an expensive keyboard.[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 to improve their competitiveness.[10] Lighter weight plastic, integrated keyboard cable, and uniform print color on the keys were some of the changes made.

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 keyboard 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]


There are numerous variations of the Model M that incorporated alternative features and also colours. One of the most popular Model M variants is the "Space Saving Keyboard" option which integrates the numpad into the main section of the keyboard; this allows an already large keyboard to become considerably smaller. A PS/2 port to USB adapter is necessary for computers without PS/2 ports and the AT Model Ms additionally require an AT to PS/2 adapter, or an SDL to PS/2 cable can be used in place of the AT one to reduce the amount of adapters used. Some PS/2 to USB adapters are unreliable because early Model M can draw more power than they expect.[12] Unicomp manufactures USB models as well as PS/2 ones obviating this issue. IBM released the regular Model M and Space Saving Keyboard Model M in an alternative 'grey / pebble' colour for use with their industrial computers: differences included a grounded space bar 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[13] 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 various models of the keyboard had small differences, while keeping the style of the key mechanism that makes the boards unique. The 1391472 model, for example, does not have a separate number pad, rather it incorporates a number pad into the body of the main keys as many laptop keyboards do. Likewise, the early 1390120 series did not feature LED indicators for the locking keys.

The Buckling spring design gives the keyboard a unique feel and sound. Unlike the common (and cheaper) dome switch design, the Model M’s buckling spring design gives users obvious tactile (a distinctive resistance as the keys are depressed) and aural (a characteristic, loud "click-clack") feedback. Many users report[who?] that they can type faster and more accurately on the Model M than other keyboards.[14][verification needed]

In addition, the Model M keyboard is 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 cracks usually fails to enter the spring mechanism. Failure of the mechanism to operate properly would require a large amount of accumulation, which is unlikely to occur.[citation needed]

There are some drawbacks to the Model M design. Because the keyboards are so heavy (over 3 lbs, heavier than some modern laptops) it is not as portable as many modern keyboards. The keys are noisy enough to be inappropriate in a location (such as a public library or office) where noise is an issue. Also, liquids spilled on the keyboard do not drain out, and remain in the keyboard with potential to cause a short circuit. The 42H1292 design, the 1993 59G780, and post-1993 1370477s and 1391401s, made mostly by Lexmark and Unicomp, include drainage channels designed to avoid this problem.


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. ^
  13. ^ US patent 4118611, Richard Hunter Harris, "Buckling Spring Torsional Snap Actuator", issued 1978-10-03  — an IBM patent for buckling spring keys.
  14. ^ "My Clickety IBM Keyboard – RIP". ASP. May 4, 2005. Retrieved January 2011. 

External links[edit]