The Model F was a series of

computer keyboards A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Replacing early punched cards and paper tape technology, i ...

produced mainly from 1981–1985 and in reduced volume until 1994 by IBM and later

Lexmark Lexmark International, Inc. is a privately held American company that manufactures laser printers and imaging products. The company is headquartered in Lexington, Kentucky. Since 2016 it has been jointly owned by a consortium of three multination ...

. Its mechanical-key design consisted of a buckling spring over a capacitive PCB, similar to the later

Model M keyboard Model M designates a group of computer keyboards designed and manufactured by IBM starting in 1985, and later by Lexmark International, Maxi Switch, and Unicomp. The keyboard's many variations have their own distinct characteristics, with ...

that used a membrane in place of the PCB. The Model F first appeared with the

IBM System/23 Datamaster The System/23 Datamaster (Model 5322 desktop model and Model 5324 floor model) was announced by IBM in July 1981. The Datamaster was the least expensive IBM computer until the far less expensive and far more popular IBM PC was announced in the fo ...

all-in-one computer. It is best known as part of the

IBM Personal Computer The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

in 1981 with some keycap label differences, and its subsequent release with the

IBM Personal Computer/AT The IBM Personal Computer/AT (model 5170, abbreviated as IBM AT or PC/AT) was released in 1984 as the fourth model in the IBM Personal Computer line, following the IBM PC/XT and its IBM Portable PC variant. It was designed around the Intel 80 ...

, where it was reconfigured with the AT protocol and some layout revisions. After the introduction of the

, production was ramped down and eventually limited to replacement units for existing installations. The capacitive design is widely considered superior to that of the later membrane design used on the Model M. It has a lighter actuation force of about 600 m N, a crisper feel, and louder feedback. It also has a higher

MTBF Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a syst ...

of over 100 million keypresses, and full n-key rollover. These advantages were sacrificed in the Model M in order to lower manufacturing costs.

Variations

Many IBM keyboards were based on Model F technology, featuring different keycaps, layouts and connections:

Enthusiasts and modern re-creation

The enthusiast community around the

also prizes Model Fs and restores them for use with modern systems, though fewer are still in use due to lower production volume and a layout that is somewhat awkward and limited by modern standards. Since 2016 a project has been underway to manufacture for sale keyboards with a faithful re-creation of the model F mechanism, completely independently of IBM. The New Model F has two variants which both resemble the 4704, but with default layouts tweaked in the direction of a Model M (notably using an inverted-T arrow-key cluster rather than the old-fashioned cross layout of the original Model Fs). This project has attracted over 25,000 subscribers and began shipping in December 2019.

Design

The Model F's key-switch design was more durable than IBM's previous beam-spring mechanism, which was prone to failure from debris and was more complex to manufacture and service. The spring assembly consisted of a top metal plate with cut holes where the plastic spring barrels reside; a bottom sheet of metal then holds the assembly together and compresses the contact sheet with a foam spacer. Earlier Model F keyboards cannot have their space bars removed without disassembling the internal assembly; this also causes a slightly different feel response from the space bar specifically: some enthusiasts modify the tension of the stabilizer on these early Model F keyboards to provide a more satisfactory response. The top metal plates in Model F keyboards are prone to corrosion and the internal foam can also rot from age, which often requires cleaning and a coating to prevent further corrosion. All Model F internal assemblies are held together with metal tabs, unlike the Model M which uses melted plastic rivets requiring more rivets to be melted on or modified with bolts. A characteristic feature of the Model F is a plastic top shell painted with a cream paint to create a rough texture. The later Model M keyboards used injection plastic rather than paint to achieve this texture. The plastic used in the Model F is quite brittle and prone to hairline cracks, and the paint can wear off from excessive use.

Comparison with Model M

Although the Model F and Model M are both based on buckling-spring technology, there are considerable differences between them:

References

External links