Model F keyboard

The Model F was a series of computer keyboards produced from 1981–1994 by IBM and later Lexmark.[1] Its mechanical-key design consisted of a buckling spring over a capacitive PCB, similar to the later Model M keyboard that used a membrane in place of the PCB.

The Model F first appeared with the IBM System/23 Datamaster all-in-one computer. It is best known as part of the IBM Personal Computer in 1981 with some keycap label differences, and its subsequent release with the IBM Personal Computer/AT, where it was reconfigured with the AT protocol and some layout revisions.[2][3]

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 mN, a crisper feel and louder feedback, and is more robust. It also has a higher MTBF of over 100 million keypresses, and full n-key rollover.

Variations

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

NamePNDescriptionImage
Model F 'XT' 1801449 Released in 1981 with the original IBM PC. Uses an XT connector.
Model F 'AT' 6450200 (US version) [4] Released in 1984 with the IBM PC AT. Uses an AT connector.
Model F '122-key terminal keyboard' 611034x Terminal keyboard released for the IBM PC 3270. Uses an IBM proprietary terminal connector.
Model F '104-key terminal keyboard' 1387033 Terminal keyboard released for the IBM 5085 and IBM 3290.[5]
Model F '4704 62-key' 6019284 62-key keyboard released for the IBM 4704[6]
Model F '4704 107-key' 6020218 107-key keyboard released for the IBM 4704
Model F '4704 50-key' 6019273 50-key keypad released for the IBM 4704
Model F 'Displaywriter' ? Keyboard released for the IBM Displaywriter System,[7] these Model F keyboards featured fully white keys.

Modern re-creation

As of 2016–2020, a project is underway to manufacture for sale keyboards with a faithful re-creation of the model F mechanism, completely independently of IBM.[8][9][10]

Design
Model F capacitive pads from an opened assembly
Corrosion occurring on a Model F 122 terminal keyboard along with dust

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.[11] 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.[12]

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 rivets requiring more rivets to be melted on or modified with bolts.[13]

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
A comparison between a Model F spring (left) and a Model M spring (right); the Model M uses a spring with fewer windings and smaller plate for the plastic membrane underneath.

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

Model FModel M
External chassis Painted plastic (zinc metal in the 4704 series) and steel metal
back panel (plastic in the F AT and zinc metal in the 4704 series)		 Molded (unpainted) plastic, plastic back panel
Internal stabilizer Only in early models
Buckling spring implementation Capacitive plate Plastic membrane
Key rollover Unlimited 2-key rollover[14]
Assembly method Reusable metal tabs Single-use rivets
Spring barrels Individually inserted in a metal plane Single plastic mold with predefined barrels

See also

References
  1. http://deskthority.net/wiki/IBM_Model_F
  2. http://deskthority.net/wiki/IBM_Model_F#IBM_System.2F23_Datamaster_Keyboard
  3. Bradley, David J. (September 1990). "The Creation of the IBM PC". BYTE. pp. 414–420. Retrieved 2 April 2016.
  4. https://deskthority.net/wiki/IBM_Model_F#IBM_Personal_Computer_AT_keyboard
  5. http://deskthority.net/wiki/IBM_Model_F#IBM_104-key_Model_F_Keyboards
  6. http://kishy.ca/?p=894
  7. http://deskthority.net/wiki/IBM_Model_F#IBM_Displaywriter_Model_F_Keyboard
  8. Limer, Eric (5 July 2017). "The Best Keyboard Ever Is Back". Popular Mechanics.
  9. Killian, Zak (6 July 2017). "Model F keyboard gets a modern reboot". The Tech Report.
  10. Strandberg, Joe. "Brand New Model F Keyboards". Retrieved 2017-07-08.
  11. http://deskthority.net/wiki/Beam_Spring#Maintenance_issues
  12. http://deskthority.net/workshop-f7/model-f-improvement-dis-assembly-tips-and-space-bar-mod-t6982.html
  13. http://wiki.geekhack.org/index.php?title=Modifications:IBM_Model_M:Nut_and_Bolt_Mod
  14. https://www.reddit.com/r/MechanicalKeyboards/wiki/nkro
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