On Jan 2, 2013, at 4:33 PM, Jordi Guillaumes i Pons wrote: Hello, The upcoming SIMH version (4.0) comes with a virtual DMC11. It has been merged to the head branch in the git repository, so I have been playing with it a little bit. The simh team has done an aswesome work again, so kudos for Bob, Mark and all the others... It seems the DMCx are supported in pdp10, pdp11 and the VAXen. The basic instructions to make it work are in the DOC files. Just to make the story short: - DMC11s work in pairs, just like the real devices. - One of the DMCs has to be put in PRIMARY mode, the other one in SECONDARY. The default is SECONDARY. Why those two modes? Real DMCs are symmetrical, I would have expected a simulation to do that too. paul