Model F keyboard

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The Model F keyboard was a series of keyboards produced in 1981 through 1994 by IBM and later Lexmark.[1] The Model F design consisted of a buckling spring with a capacitive plate design (similar to the Model M design with the exception that a rubber membrane is not used and the controller's ability to detect all keys simultaneously).[2] The keyboard is most well known for being released with the IBM Personal Computer in 1981 and later on the IBM 5170 featuring the AT protocol and some revisions to the layout, however the Model F made its debut on the IBM System/23 Datamaster.[3]

Model F keyboards are considered to be slightly more tactile than a Model M with the omission of the rubber membrane: but considerably noisier as a result of the spring plate hitting against the contact directly.

Variations[edit]

Many different keyboards were designed around the Model F technology featuring different key caps, layouts and connections.

Name PN Description Image
Model F 'XT'  ? Released in 1981 with the IBM PC 5150. Uses an XT connector. 83-key PC/XT keyboard
Model F 'AT'  ? Released in 1983 with the IBM PC 5170. Uses an AT connector. 84-key PC/AT keyboard
Model F '122-key terminal keyboard' 611034x Terminal keyboard released for the IBM PC 3270. Uses an IBM proprietary terminal connector. 84-key PC/AT keyboard
Model F '104-key terminal keyboard' 1387033 Terminal keyboard released for the IBM 5085 and IBM 3290.[4]
Model F '4704 62-key' 6019284 62-key keyboard released for the IBM 4704[5]
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,[6] these Model F keyboards featured fully white keys.

Design[edit]

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

The Model F design was more durable than IBM's previous beam spring mechanism which was prone to failure from debris and more complex to manufacture and service.[7] 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.[8]

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.[9]

A characteristic design of the Model F keyboards is that they use a a plastic top shell that's been painted with a cream paint to create a rough texture. The later Model M keyboards would use injection plastic and not paint to achieve the grainy texture. The plastic used is quite brittle and often prone to hairline cracks and the paint can wear off from excessive use.

Controller Modifications[edit]

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.[10]

Model F in contrast to the Model M[edit]

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

The Model F has a considerable amount of differences to the Model M despite both being based on the buckling spring technology.

Model F Model M
External Chassis Painted plastic Molded plastic without paint
Internally mounted stabilizer Only in earlier models No
Buckling spring implementation Capacitive plate Rubber membrane
Rollover Unlimited 2-key rollover[11]
Internal assembly reserviceable with metal tabs held together with one-use rivets
Spring barrels Individually inserted in a metal plane A single plastic mold with predefined barrels

See also[edit]

References[edit]