The great size change
In the early 1980s, the Deutsches Institut für Normung (the German Institute for Standardization) introduced workplace ergonomics standards which included requirements for how keyboards should be designed. Compliance with this standardisation led to widespread redesign of keyboards by many manufacturers.
Identity of the standard
A Guide to Human Factors and Ergonomics, Second Edition by Martin Helander (2006), page 262, references “DIN 66234” in relation to the introduction of low-profile keyboards, but not the name of the standard or which part of this standard is relevant. He in turn is referencing “Helander and Rupp, 1984”, the definition of which is not directly available via Google Books:
The German DIN 66234 standard had a pervasive effect. All computer manufacturers complied with the standard and manufactured low-profile keyboards (Helander and Rupp, 1984).
Looking at beuth.de, the relevant standard might be DIN 66234-6 “Display work stations - Design of the work station” (drafted May 1982, published December 1984), or DIN 66234-7 “Display work stations; ergonomical design of the work station; lighting and arrangement” (drafted October 1982, published December 1984). Both of these parts are contemporary with all the changes identified.
Siemens Switches and Pushbuttons Data Book (of unknown date) confirms this:
Keyboard height – important for correct working posture – in accordance with DIN 66234, Part 6 < 30 mm (measured from the desk top to the middle key row). This requirement is easily met since the key height is only 17.5 mm (with 4 mm travel) or 16 mm (with 2.5 mm travel) from the upper edge of the PC board to the upper edge of the keytop.
The same document also cites DIN standards for the standard spacing of keys:
Center spacing – important as regards finger width – in accordance with DIN 2112 and 2127 – 19.05 mm spacing for keytops
The precise requirements cannot be known without access to the relevant standard, but as noted above, it is understood that the distance from the desk surface to the top centre of a keycap on the home row must not exceed 30 mm. Amkey’s 1991 EEM entry simply refers to “30mm ergonomic requirements (DIN standard)”.
D’Milo Hallerberg, the son of Hi-Tek’s late founder and a one-time Hi-Tek employee, revealed in the Hi-Tek Corp. History topic at Deskthority:
The 725 refers to the ergonomic standard (Max .725" off the desk surface) that came out during that period that effectively obsoleted the standard series we'd been making for many years prior.
This appears to be an incorrect recollection, as a Hi-Tek (or NMB) catalogue diagram shows that the height is measured between the top of a home row keycap and the bottom of the PCB. This measurement does not take into account the bottom of keyboard enclosure (including non-slip feet) and tilt angle of the keyboard. 0.725″ is 18.42 mm, allowing the bottom of the PCB to be 11.5 mm above the desk surface.
Omron B3G-S was described in 1986 catalogue as “DIN規格に適した全高18.1mmのロープロタイプ”: “Low-profile type with an overall height of 18.1 mm suitable for DIN standards”. Here, the 18.1 mm is the distance been the standoff on the bottom of the switch and the top of the keycap.
Prior to the widespread redesigns, the keycap almost always remained above the switch at all times. Plate-mounted switches typically had the mounting plate just below the top of the switch. To meet the significant reduction in height, larger switches were required to allow the keycap to be lowered past the top of the switch. This meant that the width and depth of the switch needed to be small enough that the switch could fit inside the keycap, such as by chamfering the top edges (as with Alps) or tapering the switch body (as with Cherry). As the mounting plate would now be in the way, the position of the plate relative to the switch was also changed, with the plate being much further down, closer to the PCB.
This overall reduction in size does have ramifications for what type of switch mechanism would be permitted; for example, the extremely smooth and bouncy feel of ITT ETL18 may not be achievable in a switch reduced to DIN-compliant levels. A community attempt was made to achieve buckling spring with Cherry MX mount, but this would increase the switch height: such a design is not likely to be compliant.
Adaptation for compliance to DIN ergonomic standardisation did not require entirely new switches to be constructed, but the majority of the switch had to be redesigned. Alps had seemingly not long introduced KCC series, and when they created the DIN-compliant KCL series circa 1983 they were able to continue using their “switchplate” contact module design from KCC series. The rest of the switch was a new design. In addition to the redesigned shell, the new plunger allowed the keycap to sit lower down, and for its central post to pass inside the switch when the key is pressed; this is the origin of the famous “Alps mount” that saw widespread adoption in Asia.
Hi-Tek Series 725 required all new parts, although the contact design from the earlier High Profile and Dovetail Series switches was retained, in smaller form and with revisions to the structure. Series 725 was also introduced in 1983. Series 725 featured a radically different design, where the switch has no top at all. The plunger occupies the space where the switch top should be, functioning also as the top of the switch. The keycap then fits directly over the top of the plunger.
Cherry MX, another 1983 introduction, was a ground-up design with DIN compliance as one of a number of uncertain goals. There is no conclusive proof as to whether a click sound was intended or not, but an additional goal was the provision of hysteresis. Cherry already had a highly miniaturised switch in the form of M8, but this is not known to support alternate action (although it should be possible considering that RAFI achieved ultra-small alternate action parts) and MX also allowed Cherry to continue using their existing rotary alternate action mechanism. The shell seems to be derived from M9, but the contact system was new. It also coincided with Cherry’s adoption of lower-cost gold contacts, but those were made available for M8 and M9 switches too. Cherry MX retained a protruding stem for keycap attachment, but the stem was placed onto a platform that is lowered inside the switch. This allows the centre post of the keycap to pass inside the switch.
Omron B3G-S was also a wholly new design. It appears to have been inspired by Alps KCL/KCM and shared its keycap mount, and its contact module was based on Alps but used a contact leaf spring rather than the metal foil of KC-type Alps switches. SMK also produced switches with hollow plungers, although the standard design used SMK’s own mount. Alternative versions were produced that accepted Alps and Cherry MX keycaps.
Other product ranges changed around the same time. Somewhere around 1985, Mitsumi standard mechanical was modified similarly. Futaba appear to brought their smaller ML models to market in 1983: notable usage of these includes the Acorn Electron, Memotech MTX series and Atari 600/800XL, all introduced in 1983. The chief difference between the larger and smaller Futaba ML models is the height: this is one design that could be scaled down, although the smaller version is more fragile and not as robust. Futaba followed up with a radical redesign, the Futaba MA, shortly afterwards; this new series appears to have been introduced by 1985, but there is very little clarity on this.
The “D” in Comptec and Signature Plastics keycap family names stands for “DIN”. From the Pimp My Keyboard FAQ:
In the mid 80’s an attempt was made to standardize keycaps to a ‘DIN Standard’. DIN stands for “Deutsches Institut für Normung”, meaning "German institute for standardization". This resulted in a new high profile family being produced, the DSS family, which was a DIN standard, Spherical touch, Sculptured key family.
Comptec introduced three known DIN-compliant families: DSS, DCS (cylindrical sculptured) and DSA (spherical flat). DSS has since been discontinued, while DSA and DCS remain in production.