Tim, The drives are Diablo 30 drives, and the disks (there are several), are marked PDP-11 system disk, and PDP-11 Backup disk. The previous owner told me when I picked them up, that they should boot. Last night, I tried playing around with it again, and tried to access the disk status register (round about 17400(8) from memory, but I'm at work just now and it was late last night, so my terrible memory can't be sure...). It seemed to contain 000000 (from typing @17400/). :( Which doesn't, as far as I can tell from the assorted docs, look to promising for the state drive. An other potential problem is that I believe a clock pulse was generated by a CAMAC crate attatched to it. I've got the crate, but cannot attatch it at present because it needs a 110V supply, and I don't have my 110V transformer just now. My house is a 240V only zone at the moment, or at least as long as these machines stop tripping the surge detector!. I need to install a more forgiving fuse box. Thanks for your help. Grant