Model M

Model M
Among the first IBM Model Ms. This particular unit was manufactured in 1986.
Part no.	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

Model M is a designation for a group of computer keyboards manufactured by IBM starting in 1984, and later by Lexmark, Unicomp and MaxiSwitch. The keyboard's many variations 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.

The Model M is also regarded as a timeless and durable piece of hardware. 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 and ISO 102-key layouts. Since their original popularity, new generations of writers and computer technicians have rediscovered their unique functionality and aesthetics. The Kentucky-based company Unicomp continues to manufacture and sell Model M-style keyboards.

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.