Model F keyboard
| Company type | Product line |
|---|---|
| Industry | Computer peripherals |
| Founded | 1981 |
| Founder | IBM |
| Defunct | 1994 (limited production ended) |
| Successor | Model M keyboard |
Area served | Worldwide |
| Products | Computer keyboards |
The Model F series consisted of computer keyboards primarily manufactured between 1981 and 1985, with limited production continuing until 1994 by IBM and subsequently Lexmark. Its mechanical architecture utilized a buckling spring mechanism positioned above a capacitive PCB, distinguishing it from the membrane-based design found in the later Model M keyboard.
Introduced alongside the IBM System/23 Datamaster, the Model F is most recognized for its use in the 1981 IBM Personal Computer, featuring some variations in keycaps, and later in the IBM Personal Computer/AT, where it adopted the AT communication protocol and updated layout.[1][2] Following the release of the Model M keyboard, production of the Model F diminished, primarily shifting to manufacturing replacement units.
The capacitive switch design of the Model F is widely regarded as superior to the membrane switches in the Model M,[3] delivering a lighter actuation force (approximately 600 mN), more precise tactile feedback, louder audible response, enhanced longevity (mean time between failures exceeding 100 million keystrokes), and full n-key rollover capability. These performance advantages were compromised in the Model M to achieve cost reductions during manufacturing.
Variations
Multiple IBM keyboards incorporated Model F technology, differing in keycap styles, layouts, and connector types:
| Name | PN | Description | Image |
|---|---|---|---|
| Model F 'XT' | 1801449 | Launched in 1981 with the original IBM PC; equipped with an XT connector. | |
| Model F 'AT' | 6450200 (US version) | Released in 1984 alongside the IBM PC AT; features an AT connector. | |
| Model F '122-key terminal keyboard' | 611034x | Terminal keyboard designed for IBM PC 3270 and other IBM terminals; utilizes a proprietary terminal connector. | |
| Model F '104-key terminal keyboard' | 1387033 | Terminal keyboard compatible with IBM 5085 and IBM 3290 systems. | |
| Model F '3178 blue switch 87-key' | 6019284 | Produced for IBM 3178 terminals; named after the blue toggle switch on its upper half. | |
| Model F '4704 62-key' | 6019284 | A compact 62-key keyboard designed for IBM 4704. | |
| Model F '4704 107-key' | 6020218 | Full-sized 107-key keyboard variant for IBM 4704. | |
| Model F '4704 50-key' | 6019273 | A 50-key keypad tailored for IBM 4704 systems. | |
| Model F 'Displaywriter' | ? | Keyboard created for the IBM Displaywriter System, notable for its all-white keycaps. |
Enthusiasts and modern re-creation
Despite its lower production volume and a layout that is less aligned with contemporary preferences compared to the Model M keyboard, the Model F maintains a dedicated following among enthusiasts who restore these keyboards for current use.
Beginning in 2016, an independent initiative has been producing keyboards that faithfully replicate the original Model F mechanism. The New Model F project offers two models inspired by the 4704 design but incorporates layout modifications trending towards a Model M style, such as replacing the original cross-shaped arrow key cluster with an inverted-T configuration. This effort has attracted over 25,000 supporters and commenced shipments in December 2019.
Design
The key-switch mechanism of the Model F represented an advancement over IBM’s prior beam-spring design, which was vulnerable to failure caused by debris ingress and was challenging to repair. Its spring assembly consists of a top metal plate perforated with holes that house plastic spring barrels, secured by a bottom metal sheet that compresses a contact layer separated by a foam spacer. Early versions of the Model F require complete disassembly to remove the space bar, influencing its tactile characteristics; some users adjust stabilizer tension to enhance responsiveness.
The top metal plates are prone to corrosion over time, and internal foam components may deteriorate with age, often requiring cleaning and application of protective coatings. Unlike the plastic rivets used in Model M assemblies, Model F keyboards employ metal tabs for increased structural integrity.
A distinctive aspect of the Model F is its plastic top shell coated with cream-colored paint to provide texture; subsequent Model M versions transitioned to textured injection-molded plastic. The plastic material used in the Model F is brittle and susceptible to hairline fractures, while frequent usage can cause paint wear on its surface.
Comparison with Model M
Although both the Model F and Model M employ buckling-spring mechanisms, several notable distinctions set them apart:
| Model F | Model M | |
|---|---|---|
| Outer casing | Painted plastic (zinc metal used in 4704 series) combined with a steel back panel (plastic in F AT, zinc in 4704) | Molded, unpainted plastic housing with a plastic back panel |
| Internal stabilizer | Found exclusively in early versions | |
| Buckling spring design | Capacitive sensing plate | Plastic membrane layer |
| Key rollover capability | Unlimited rollover support | Limited to 2-key rollover |
| Construction technique | Metal tabs designed for reuse | One-time use plastic rivets |
| Spring barrel configuration | Each barrel individually placed within a metal plate | Integrated single plastic mold containing fixed barrels |
See also
- Model M keyboard
- IBM PC keyboard
- IBM Displaywriter System
- IBM System/23
- List of mechanical keyboards
External links
- Model F Labs – current manufacturer of the Model F.
- The Compleat Classic Keyboard (Eric S. Raymond) – insights on compatibility with modern hardware.