Thanks for the suggestions so far. I tried a few things with the following to report: I verified the copy of RT-11 on RX-01 floppy. It boots fine on the LSI-11 system it was built on, tried "BOOT RT11SJ" as well as with the "/FOREIGN" option and it ran fine on that system (which has an M7946 controller). The drive is configured for RX-01 mode only (since these are the only controllers I have in both Q-Bus and Unibus flavour). Now, put that same drive on the 11/34 CPU with an M7846 card. Checked the CPU carefully: NPG jumpers are all intact on the backplane (CA1-CA2) and all unused slot D's have a grant continuity card. Just to ensure it works I reconfigured the console for 9600 baud (originally 300) and ran a simple "echo" program loaded at 001000 which runs fine (so it can store programs in memory and the execute them). The system has loads of memory - three cards with 16K, 48KW, and 96kW on them - so I did a quick check at locations 100000 and 700000 and memory is certainly there. Tried typing-in the RX-01 bootstrap and running it: same as before, stops with "005134" on the display. Added an M9301 card to avoid having to type-in the bootstrap each time (also, slot 3AB of my system was empty ... no terminator, nothing .... should have a terminator in that slot regardless and I should have added this card long ago). Now, I can just start the 11/34, and start the bootstrap ROM (with console emulator) at 773000. I get the four registers displayed as expected and the "$" prompt. Typed "DX0" to boot from the floppy. The heads engage and I can hear the heads stepping: Step, short pause, and three more steps, and then it halts again: "005134" on the display (when that address is examined, the contents are "000400"). Any further thought on how do diagnose this one would be appreciated! Jerome: this is my personal "baby" which I have owned even before I went to engineering school. Now just part of a personal collection of interesting technology. I _had_ three RK-05 drives on the system at one point but those drives were stored very improperly and were completely destroyed (the system worked about 20 years ago with those drives and oddly, never had an M9301 installed - that slot was always empty). Now, I am just salvaging what was left working ... in my case I was very lucky that the CPU seems unscathed by the ravages of time! The RX-01 controller was picked-up a few years ago in the hopes I could make a basic system again with an RX-01 drive. Cheers ... Mark Professor Mark Csele, P.Eng. Niagara College, Canada 300 Woodlawn Rd., L-23 Welland, ON, L3C 7L3 (905) 735-2211 x.7629 E-Mail: mcsele at niagarac.on.ca URL: http://technology.niagarac.on.ca/people/mcsele Author of "Fundamentals of Light Sources and Lasers", Wiley, 2004