How do you know that you've got an 11/84 "capable" 11/84? There were many revisions: A M8190 without any suffixes is a 15 MHz (11/73) CPU with an unusable socket for the FPJ11 floating point processor. A M8190-AB is a 15 MHz (11/73) CPU with "warm floating point", but *will* accept the FPJ11 as an option. A M8190-AC is still a 15 MHz (11/73) CPU, with a FPJ11 factory installed. A M8190-AD is a 18 MHz (11/83 or 11/84) CPU with "warm floating point", taking the FPJ11 as an option. A M8190-AE is a 18 MHz (11/83 or 11/84) CPU with the FPJ11 factory installed. Even the above suffixes don't actually pinpoint the exact revision of the CPU with respect to FPJ11 bugs, but they serve as a starting point. To further complicate matters, within digital the CPU is identified differently based on whether it has PMI memory installed or not. (And, of course, it matters whether the PMI comes before or after the CPU in the backplane!) So, for example, you may find a 18 MHz CPU with non-PMI memory called a 11/73, but with PMI memory it's called a 11/83. An 11/84 is a 18MHz KDJ11-B with PMI memory and a KTJ11-B Unibus adapter tacked on. I'm pretty sure the M8190 ROM's are the same whether it's to be used as a 11/84 or an 11/83, and that the Unibus boot ROM functionality is added in the KTJ11-B, which somehow coordinates these issues with the CPU. (It's explained in the KTJ11-B processor handbook, but I never read through it all without falling asleep.) To a large extent, all this confusion is caused by the desire for folks to say "this machine is a 11/x3" where x is 7 or 8. If you really insist on the official classifications, you have to read three of the Micronotes: uNote 25: FPJ11, KDJ11-A compatibility uNote 30: PMI on KDJ11-B and MSV11-J uNote 39: KDJ11-A and -B differences. The above micronotes - and many more - available from: http://sunsite.unc.edu/pub/academic/computer-science/history/pdp-11/hardwar… If, indeed, you have the 11/84 capable version, you'll also need the KDJ11-B and the 11/84 backplane, along with PMI memory, to have a real 11/84 CPU. I've got several in use as "11/73B"'s. -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology Voice: 301-767-5917 7328 Bradley Blvd Fax: 301-767-5927 Bethesda, MD, USA 20817