Model F keyboard
The Model F was a series of computer keyboards produced from 1981–1994 by IBM and later Lexmark. Its mechanical-key design consisted of a buckling spring over a capacitive PCB, similarly to the later Model M 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 5170, where it was reconfigured with the AT protocol and some layout revisions.
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 60g, 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.
The sound of an IBM Model F from 1984.
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Many IBM keyboards were based on Model F technology, featuring different keycaps, layouts and connections:
|Model F 'XT'||1801449||Released in 1981 with the IBM PC 5150. Uses an XT connector.|
|Model F 'AT'||6450200 (US version) ||Released in 1983 with the IBM PC 5170. 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.|
|Model F '4704 62-key'||6019284||62-key keyboard released for the IBM 4704|
|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, these Model F keyboards featured fully white keys.|
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 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.
It is possible to use a programmable micro-controller to connect to a Model F controller and convert it to a USB-capable device for unlimited rollover, along with modifying the layout to ANSI. These exist both as external converter boxes, and complete replacements of the internal electronics.
Comparison with Model M
Although the Model F and Model M are both based on buckling-spring technology, there are considerable differences between them:
|Model F||Model 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|
|Assembly method||Reusable metal tabs||Single-use rivets|
|Spring barrels||Individually inserted in a metal plane||Single plastic mold with predefined barrels|
- Bradley, David J. (September 1990). "The Creation of the IBM PC". BYTE. pp. 414–420. Retrieved 2 April 2016.
- Limer, Eric (5 July 2017). "The Best Keyboard Ever Is Back". Popular Mechanics.
- Killian, Zak (6 July 2017). "Model F keyboard gets a modern reboot". The Tech Report.
- Strandberg, Joe. "Brand New Model F Keyboards". Retrieved 2017-07-08.
- "XT/AT/PS2/Terminal to USB Converter with NKRO". geekhack keyboard enthusiasts. 22 April 2011. Retrieved 2017-07-08.
- "xwhatsit's Grand Unified IBM Capsense USB controller thread". geekhack keyboard enthusiasts. 11 May 2014. Retrieved 2017-07-08.