Someone (not me) in Germany is selling a number of cards from a HP21MX
machine. Some boards have date codes from 1974 so I guess it is an M-series.
Not sure what cards there are in this lot, but it is for sure the CPU
boards itself, some memory boards and what looks like some serial boards.
http://www.ebay.de/itm/16-Neuwertige-HP-Speicher-Platinen-und-andere-/23153…