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Cherry M11

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Overview

Cherry M11 is a customer-specific series created for HP as a drop-in replacement for Datanetics DC-60 series, with the dimensions matching those of DC-61-06. The most telling characteristic is that, unlike all other contemporary hard contact Cherry switches, M11 is single-pole only, with the internal arrangement adjusted to move the terminals to the centreline. In effect, M11 is an M8 or M9 switch rearranged to match the dimensions and keystem of DC-60. Switch travel is also reduced to 3.175 mm, to match DC-60’s travel of 3.18 mm.

DC-60 itself was introduced in 1973, primarily for Monroe, as a low-cost switch for high-end calculators. The M11-0101 drawing itself is dated November 1979, placing it well after DC-60 was introduced. M11 is however based on the tallest type (DC-61-05/DC-61-06), whose introduction seems to be between 1975 and 1981.

M11 is only known from HP keyboards, and has two discovered variants:

This customer part number on the M11-0101 drawing is one that HP had assigned to a model of DC-60 switch, which is the model that M11-0101 was expected to substitute. The HP 9825 service manual—which depicts a Datanetics DC-60 switch in the section of keyswitch removal—lists these three switch types in the parts list on page 6-7:

HP part Description
3101-2390 All Small and Normal Size Keys
3101-0468 Store, Continue, Execute (Double Size Keys)
3101-0469 Spacebar

The Cherry B21E-A601 keyboard for the HP 9835 (which uses M11 switches) bears customer part number 3101-0436-1 REV.G, which is clearly related. Sadly this later keyboard is missing from the HP 9835 service manual, which only covers the older chiclet type prior to the Cherry keyboard being adopted.

The 9825 service manual depicts one of the switches, which is clearly DC-60, and indicates that all three look the same, differing only in spring strength and lubricant used. The 9825 keyboard shown at Deskthority is an exact match for that in the service manual, and it is stamped “DNC” for Datanetics Corporation. It is the space bar switch part number from this keyboard that was passed to Cherry when M11-0101 was commissioned. (That is also the forum topic where, in 2014, Findecanor originally made the connection between M11 and DC-60, before DC-60 had been identified, hence no-one recognising the manufacturer stamp on the PCB.)

UncleFan supplied the following photo from Brother Dragon (yab8433408) showing an HP keyboard with what appear to be the MX-mount DC-60 switches, alongside an M11-0101 for space:

Confusingly, these cream switches are (in the examples previously found for sale separately) the medium profile type, which makes them distinctly shorter than M11. At present, nothing more is known about the keyboard shown above.

For a long time, the name of the series was a mystery. The part numbers follow the old system used by M4–M7, which would suggest a series name of M1, although initially the name M11 was chosen instead. Günter Murmann (formerly Cherry’s VP of Engineering in Germany) confirms that this is M11 series, not M1.

Documentation

See also