Model M keyboard

History

The Model M was designed to be more cost effective than the Model F keyboards it replaced. Production of Model M's began in 1985; they were often bundled with new IBM computers. They were produced at IBM plants in Lexington; Greenock, Scotland and Guadalajara, Mexico. The most common Model M variant is the part number 1391401, the US English layout keyboard of the IBM PS/2. Until around 1993, most Model M's included a sturdy, coiled, detachable cable, with either an AT (pre-1987) or PS/2 connector, in 5- and 10-foot lengths (1.5 and 3 metres). From about 1994 onwards, flat non-detachable cables were used to reduce manufacturing costs; however, IBM retained its 101-key layout, never implementing the Microsoft Windows keys common on other keyboards from that time. Unicomp later designed a 104-key Model M with Windows 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. Lexmark continued manufacturing the Model M in the United States, United Kingdom and Mexico, with IBM being Lexmark's major customer. Many of these keyboards had IBM assembly part numbers such as 52G9658, 52G9700, 82G2383 and 42H1292. Due to pricing pressures, many Model M's in this period were manufactured with a new lower-cost design including lighter plastic, an integrated cable, and a single color for key legends.

On March 27, 1996, Lexmark's contract to make keyboards for IBM expired, and Lexmark transitioned its keyboard business to IBM and other vendors. Some of its manufacturing assets were sold to a group of Lexmark employees, who formed Unicomp. Unicomp still manufactures its version of the Model M (similar to part number 42H1292 but first renamed 42H1292U and subsequently the "Customizer"), as well as other configurations including updated 104- and 105-key layouts; a Unix layout (where the Ctrl and Caps Lock keys and Esc and tilde keys are transposed); models with integrated pointing sticks or trackballs; and POS-specific models such as those with built-in magstripe readers. When Lexmark discontinued keyboard production in March 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. These companies stopped producing Model M's 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.

Variations

The Model M's numerous variations (referred to as "part numbers") incorporated alternative features and/or colors. 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 standard and Space Saving Model M's in an alternative 'gray/pebble' colour for use with their Industrial computers; this darker color was designed to conceal discoloration from handling in production environments. Other variable features include a grounded spacebar and, on some later models, drainage holes to deter damage from spilled drinks.

Design

The variant most commonly referred to as "Model M" is Part No. 1391401, on which many other variants were based. This Enhanced Keyboard model included IBM's patented buckling spring design and swappable keycaps.

The Model M's design has been widely praised as durable and reliable, and has remained basically the same since the 1980s, while virtually all other computing hardware, from PCs to monitors to mice, has changed dramatically. The M's sturdy design, including its heavy steel backplate and strong plastic frame, has allowed even the most abused examples to survive for years.

The Model M's buckling spring key design gives it a unique feel and sound. Unlike more common and cheaper dome switch and membrane designs, buckling springs give users unmistakable tactile and auditory feedback. Because of its more defined touch, some users report they can type faster and more accurately on the Model M than on other keyboards.

The Model M is also less susceptible to dirt and wear. Dirt can interfere with the proper operation of most other keyboard technologies; however, the buckling spring switch's design is such that any dirt that falls between the keys is unlikely to enter the switch mechanism, which is covered by the key. Even if dirt were to enter a mechanism, a large amount would be necessary to prevent it from operating.

Until the late 4th-generation variants, most Model M's have a 1.25" slotted, circular speaker grille in their bottom surfaces. Relatively few contain an actual speaker, however, which was useful only for sounding beep codes on older terminal systems. The most common p/n's with speakers are 1394540 and 51G872, made for RS/6000 UNIX workstations.

There are some drawbacks to the Model M design:

Identification

All Model M keyboards made by IBM and Lexmark have an ID label on the underside indicating the assembly part number, individual serial number, and manufacturing date. The general period in which a Model M was made can also often be distinguished by the type of logo "badge" above its keys. The first model M's (part numbers 1390120 or 1390131) have a square aluminum logo badge in the top right corner. Part number 1391401, and most variants based on it, has a gray IBM logo in a recessed oval at the board's upper left. Later IBM-made Model M's, and variants subsequently made by Lexmark in the early 1990s (part numbers 1370477, 52G9658, 52G9700, 59G7980, 92G7453, 82G2383, 42H1292, etc.) have a similar oval badge area with a blue logo.

Features by part number

Logo position legend:

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Note: Manufacture dates are approximate.