Jerome Fine replies: Has anyone helped in this request? I believe that the following is true: BA23: First 3 slots are ABCD Next 5 slots are ABAB or Q22 In short, you can place only one board in the first 3 slots. If the board is a dual, you loose the other half. The last five slots are able to use either a quad or 2 duals. The bus grant loop is serpentine. 1A, 2A, 3A, 4A, 4C, 5C, 5A, 6A, 6C, 7C, 7A, 8A, 8C. 1 -> 2 -> 3 -> 4 -> -> 5 <- <- 6 -> -> 7 <- <- 8 -> -> The BA123 is identical EXCEPT that slots 1,2 3,4 are all ABCD. If you want the loop diagram for the Ba123, please respond. Which operating system do you use on the PDP-11? If it is RT-11, I would like to keep in touch. I notice that you have not responded to my e-mail of Monday. If there is no further response, I will just assume that you are not very interested in RT-11. For anyone else (Allison??) who is interested in RT-11 software, a response would be appreciated. I think I understand that the hardware is the most important aspect to most of the individuals on this list. I am one of the exceptions in that the software is the most important with the hardware being a close second until a few months ago when it became possible to run PDP-11 programs on a PC, in particular RT-11 programs and the operating system plus all modules. One day I even booted a TU-58 from 1978 with a tape cartridge holding files from a 1978 version of the RT-11 operation system (V3.0B). While the TU-58 was connected to a COM port on the PC which was running an emulator program which allowed the PC to look like a PDP-11 to the TU-58, it was still quite a thrill to be able to boot the 20 year old TU-58 with 20 year old software. Is there anyone else also interested in RT-11 software? Sincerely yours, Jerome Fine RT-11/TSX-PLUS User/Addict Year 2000 Solutions for Legacy RT-11 Applications (Sources not always required)