Yeah, but not much has to be working for that to happen! :-) Yes, you can - but having a slot with no NPG jumper, and either i) no board in in it at all, or ii) a non-DMA-speaking board in it, will prevent any DMA device _further down the bus_ from working. No. It needs a MUD slot (UNIBUS in connectors A-B, essentially; more here: http://gunkies.org/wiki/Modified_UNIBUS_Device although other places have info about this too). (I'm not exactly sure how the A/B connectors on DD11-B slots 2 and 3 are wired, it's something wierd, look at the DD11-B prints for more.) The NPG jumper is IRRELEVANT to everything except DMA devices (in that slot, and downstream). Well, technically speaking, that's not entirely accurate - clearly, from the below typing "r" doesn't crash the machine. I gather you meant 'typing "{anything}<CR>" crashes the machine'. Hmm. That sounds like the bootstrap isn't running properly. Oh, I remember an issue I had with the boostrap when first trying to bring up Unix in Ersatz-11 - does your -11/40 have the EIS board? Is the EIS working? If not, the bootstrap won't run - it uses the MUL instruction. (MUL is not in the base set on an -11/40, it's an option.) If that's not it, we'll have to debug the bootstrap... Should't be too hard, test versions can be loaded directly into memory with GUI-11, we don't have to write them to disk. You've got a (hopefully good) disk to have the bootstrap ponder over... Noel