Cherry M4/M5/M6/M7: a single series?
I received some Cherry M94A-18NI switches from Nuum at Deskthority. According to the Cherry Keyboards and Switches Catalogue 1982, these should be M93A-19NN. Nuum’s box was labelled “86 05 14 04 1 08 12”, suggesting a production date of 1986-05-14. The implication here is that revisions to the manufacturing process and design required new part numbers to be assigned.
From this, I have a theory: M4, M5, M6 and M7 represent nothing more than product revisions to the original gold crosspoint series.
In Cherry’s Switches & Keyboards Catalog C-73, these switches had no name: they were referred to as ‘Cherry low profile key switches with gold “crosspoint” contacts’, or simply “Cherry Key Modules”. Part numbers took the forms M61-0nnn and M62-0nnn; M01-0005 was an adapter part for lit switches. In 1973, Cherry had no other comparable offerings, so there was no need to distinguish these switches from any other. (Even the description “low profile” was re-used for later modules, disqualifying that from being used as a description; M7 became “Standard Mounting Height” in comparison to M9 and M8.)
The C-74 catalogue offered nothing different. After this, things become strange. Cherry Keyboards catalogue KB79-2R, printed in May 1982, gives part numbers from M41-01nn up to M71-01nn, with no insight into why part numbers begin with each of M41, M51, M61, M62 and M71. Each of these prefixes appears to be on equal footing. There is even a tactile version, M51-0229. M4 and M5 are listed in this catalogue despite being completely absent in previous catalogues, which does correspond to M51-0131 having a newer style and seemingly newer-style internals; it calls into question whether these part numbers were actually assigned in numerical order, or whether Cherry started counting backwards from M6 down to M4. However, it is worth noting that the the design drawing for M51-0129/0131 goes back to 1973.
Cherry Keyboards and Switches Catalogue 1982 supplemented the “Standard Mounting Height” Serie M7 with the “Low Profile” Serie M9, and “Super Low Profile” M8. The part numbers are rather strange. M7 now has part numbers from M71-0nnn to M78-0nnn (every prefix except M72, which does not appear), while M8 uses M81A-nnnn and M9 uses M93A-nnnn. Why M9 has a higher series number and higher prefixes, is a mystery.
Cherry issued a last-time buy notification for the M8 series in October 2013, and Deskthority obtained a batch of switches with part number M84-0100. There is a different reason for the change from M81 to M84 however: the second digit indicates the grade of switch (contact material and voltage and current limits).
There is not enough data yet to provide proof that M4 through M7 are all the same series, but it would explain why the part numbers seemed to change randomly. The introduction of newer switch designs required Cherry to name the series as M7, and lock a section of each part number to the series name. As such, this move on Cherry’s part might be seen as a justification for referring to the whole series as “M7” in spite of lower part number prefixes, as this was the first time that Cherry ever assigned it a series name of its own.
A note on age
The C-73 and C-74 catalogues both state:
Another CHERRY design first. Gold “Crosspoint” Contact Switch (two Gold prisms at right angles to each other) has provided highly reliable keyboard switching for several years in thousands of the most sophisticated electronic desk top calculators and computer terminals.
Catalogue KB79-2R is cited as being printed in May 1982, but its version of the story is as follows:
This is another Cherry design first: A Gold “Crosspoint” Contact Switch — two gold prisms at right angles to each other. This design has provided highly reliable keyboard switching for nearly 10 years in tens of thousands of the most sophisticated, most demanding applications.
1982 subtract 9 would be 1973, which is not “several years” before catalogue C-73. It is more likely that KB79-2R was originally written in 1979, giving an introduction date of this switch series as 1969 or 1970.
For source material, see: