The great size change
When Alps superseded SKCC series with SKCL series, the switchplate design was retained intact. Since the switchplate—which gives “complicated Alps” its moniker—is the expensive part of the switch, what was the rationale for the redesign? There is no indication that it was done to reduce costs.
Hi-Tek Series 725 (“Space Invaders”/“Fury Bear”) is so named because the total height is a maximum of 0.725″ off the desk surface. In private conversation, former Hi-Tek Corporation employee and founder’s son D’Milo Hallerberg referred to an unspecified German (DIN) standard, of which compliance was the cause for the redesign of the existing Hi-Tek High Profile switch. The Series 725 switch was designed in 1982, and was introduced in 1983, the same year that Alps SKCL was introduced. (It was my conversation with D’Milo that led me to recognise how all these changes seemed to fit together.)
Cherry MX was also introduced in 1983, and was also a size reduction on the M9 switch on which it appears to have been based. Cherry M9 retained the old-school design of having the mounting plate at the top of the switch. Just as with Alps SKCC and old SMK and Futaba switches, very little of the switch is visible above the plate. In addition, it was common for no part of the keycap stem to ever travel lower than the top of the switch: the keycap would often sit high up on the slider, and when the key was fully depressed, the keycap stem would be resting on the top of the switch.
Alps SKCL, Cherry MX, and 1985’s SMK second generation all positioned the mounting plate much lower down, with around half the switch visible above the plate. Also, each design found a way to allow the keycap stem to be lowered right down inside the switch. Cherry achieved this by putting a platform around the slider stem, as well as clearance notches in the upper shell. Alps inverted the slider so that the keycap stem fits inside, so there is nothing to collide with the top of the switch, and Omron and SMK followed suit (SMK around 1985, it appears). In fact, the Omron B3G-S catalogue page that I received specifically notes (if I have transcribed it correctly), “DIN規格に適した全18.1mmのロープロタイプ”, or “Low-profile type of all 18.1 mm suitable for DIN standard”. Comparing the drawings from B3G and B3G-S, I can see that the PCB-to-plate distance was reduced from 10 mm to 4.5 mm, allowing the keycap to be lowered down over the switch shell.
Hi-Tek Series 725 featured a radically different design, where the switch has no top at all. The slider occupies the space where the switch top should be, serving both as the switch top and the slider. The keycap then fits directly over the top of the slider.
Other keycap families changed around a similar time. Somewhere around 1985, Mitsumi standard mechanical was modified similarly. Futaba “low-profile linear”, a derivative of the short-lived “simplified linear”, appears to have been introduced in 1983: notable usage includes the Acorn Electron, Memotech MTX series and Atari 600/800XL, all introduced in 1983. The chief difference between the simplified linear switch and the low-profile linear is simply a reduction in height; unlike with other switch families, the PCB-to-plate distance remained high (around twice that of SKCL) and the keycap stem could not descend inside the switch. Futaba followed up with a radical redesign, the “Futaba clicky switch”, shortly afterwards; this new series appears to have been introduced by 1985 (we have no accurate dating evidence recorded for the keyboards known to use the old-style clicky switch).
Identity of the standard
Although various mention has been made of this German standard, the standard has never knowingly been mentioned at Deskthority or Geekhack or by any vendor or manufacturer.
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 defintion 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.
This does not specifically provide the origin of the figure 0.725″, although that equates to 18.415 mm, which is only marginally more than the key height figures given by Siemens.
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
Signature Plastics keycaps
As an aside, the “D” in 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.
Updated 2016-02-14 to mention the official DIN-compliance of Omron B3G-S.