Hi, in my VAX 11/780 I have the PDP-11/03 alias KC780. And it has the following memory board right now: M7944 MSV11-B Q 4-Kword 16-bit MOS RAM (external refresh) But, since I'm planning to upgrade to an 11/785 I need additional RAM. When it showed up on ePay I buyed a M8044-DA MSV11-DD Q 32-Kword 16-bit MOS RAM but the boot program will not load with this. Why would that be? From the error I got it appeared as if may be there is just some jumpering to do, but I have no clue as to where and what. Looking at the UNIBUS/Q bus field guide beginning from M7944 and then scanning forward to the next MSV11 I find: M7955-AD MSV11-CD Q 16-Kword 16-bit MOS RAM with on-board refresh and then the family of M8044s M8044-AA MSV11-DA Q 4-Kword 16-bit MOS RAM M8044-AA (Also M8044-AB, -AC, -AD) M8044-AA Refs: EK-MSVI1-OP, MP-00566 M8044-BA MSV11-DB Q 8-Kword 16-bit MOS RAM M8044-BA (Also M8044-BB, -BC, -BD) M8044-BA Refs: EK-MSVI1-OP, MP-00566 M8044-CA MSV11-DC Q 16-Kword 16-bit MOS RAM M8044-CA (Also M8044-CB, -CC, -CD, -CE, -CF, -CH, -CL, -CM) M8044-CA Refs: EK-MSVI1-OP, MP-00566 M8044-DA MSV11-DD Q 32-Kword 16-bit MOS RAM M8044-DA (Also M8044-DB, -DC, -DD, -DE, -DF, -DH, -DL, -DM) M8044-DA Refs: EK-MSVI1-OP, MP-00566 Does that mean that I should have the M7955-AD RAM instead? This is confusing. And I'm not even asking for Q22 bus or PMI memory stuff. What's the thing I'm missing? thanks, -Gunther -- Gunther Schadow, M.D., Ph.D. gschadow(a)regenstrief.org Medical Information Scientist Regenstrief Institute for Health Care Adjunct Assistant Professor Indiana University School of Medicine tel:1(317)630-7960 http://aurora.regenstrief.org