Model F keyboard
Capacitive buckling-spring keyboard, predecessor to the Model M.
The Model F is a series of computer keyboards primarily manufactured from 1981 to 1985, with limited production continuing until 1994, by IBM and later Lexmark. Its mechanical design uses a buckling spring mechanism over a capacitive printed circuit board (PCB), a technology similar to the later Model M, which replaced the PCB with a membrane. The Model F debuted with the IBM System/23 Datamaster all-in-one computer and is most famous for its inclusion with the 1981 IBM Personal Computer, followed by a revised version for the IBM Personal Computer/AT that introduced the AT protocol and layout changes. The capacitive design is generally regarded as better than the Model M’s membrane approach, featuring a lighter actuation force of about 600 mN, a sharper feel, louder feedback, a mean time between failures exceeding 100 million keypresses, and full n-key rollover. These benefits were traded off in the Model M to reduce production costs. Variations of the Model F included many IBM keyboards with different keycaps, layouts, and connections. From April 1986 IBM shipped the PC AT and PC XT with the Model M keyboard. Enthusiasts who prize the Model M also value Model Fs, restoring them for modern use, though fewer remain in active service due to lower production numbers and a layout considered somewhat awkward and limited by today’s standards. Since 2016, a project has worked to manufacture and sell keyboards that faithfully recreate the Model F mechanism independently of IBM. The New Model F comes in two variants, both resembling the 4704 but with default layouts adjusted toward the Model M—notably using an inverted-T arrow-key cluster instead of the original cross layout. This project has gained over 25,000 subscribers and began shipping in December 2019. The Model F’s key-switch design proved more durable than IBM’s earlier beam-spring mechanism, which was prone to debris-related failure and more complex to build and maintain. The spring assembly consists of a top metal plate with cut holes for plastic spring barrels, a bottom metal sheet that holds the assembly together, and a foam spacer compressing the contact sheet.
- Production years
- 1981–1985 (main), until 1994 (reduced volume)
- Manufacturers
- IBM, later Lexmark
- Actuation force
- about 600 mN
- Mtbf
- over 100 million keypresses
- Rollover
- full n-key rollover
- First appearance
- IBM System/23 Datamaster
- Notable use
- IBM Personal Computer (1981), IBM Personal Computer/AT
Lore & Background
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 more complex to manufacture. The spring assembly consisted of a top metal plate with cut holes for plastic spring barrels, a bottom sheet of metal holding the assembly together, and a contact sheet with a foam spacer. Earlier Model F keyboards cannot have their space bars removed without disassembling the internal assembly, causing a slightly different feel response; some enthusiasts modify the stabilizer tension on these early models. The top metal plates are prone to corrosion and the internal foam can rot from age, often requiring cleaning and coating. All Model F internal assemblies are held together with metal tabs, unlike the Model M which uses melted plastic rivets. A characteristic feature is a plastic top shell painted with cream paint to create a rough texture; the plastic is brittle and prone to hairline cracks, and the paint can wear off from excessive use.
Reader's Guide
The Model F is significant as the direct predecessor to the more widely known Model M, and its capacitive design is widely considered superior in feel, durability, and functionality. It offered a lighter actuation force of about 600 mN, a crisper feel, louder feedback, a higher MTBF of over 100 million keypresses, and full n-key rollover—advantages sacrificed in the Model M to lower manufacturing costs. After the Model M's introduction in April 1986, Model F production was ramped down and eventually limited to replacement units for existing installations. The enthusiast community around the Model M 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 considered 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, independently of IBM; the New Model F has two variants resembling the 4704 with default layouts tweaked toward the Model M, attracting over 25,000 subscribers and beginning shipping in December 2019.
Did You Know?
- The Model F was produced mainly from 1981–1985 and in reduced volume until 1994 by IBM and later Lexmark.
- Its capacitive design is widely considered superior to the membrane design of the Model M, with a lighter actuation force of about 600 mN.
- Since 2016, a project has been manufacturing a faithful re-creation called the New Model F, which began shipping in December 2019.
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