Jerome Fine replies: Your suggestion might not be possible. I once had the box and boards for an 11/94. I really can't remember, but there might not have been any slots for the memory. In any case, I am extremely curious. What goal(s) will you achieve? Do you want to run software faster? Is your only goal to have the fastest PDP-11 that DEC ever produced? Note that a number of other companies produced much faster PDP-11 CPU boards. Note that I very much appreciate that from a hardware point of view your goal is extremely gratifying - probably even more than my software goals. I am just curious what your goals are. One of my goals when I run using PDP-11 software is to run as fast as possible. At present I run at about 15 times a PDP-11/93. Very shortly, I hope to be upgrading my hardware and be able to run at 100 times a PDP-11/93 along with the availability of having an extra GigaByte of spare memory for data that may also allow a co-processor to perform CPU intensive calculations. About 20 years ago, I was using a PDP-11/23+ on a system with 4 MB of memory which included a co-processor that used the same memory as the PDP-11/23+. Any finally, although my experience is with an 11/93 on the Qbus, I found that there is very little difference between an 11/93 and an 11/83 as far as CPU speed is concerned. That would also be likely to apply to the difference between an 11/94 and an 11/84. Basically, I suggest that the only difference in speed is due to the clock rate of 20 MHz on the 11/93 board and the 18 MHz clock rate (or crystal if you prefer) on the 11/83 board. Otherwise, the PMI memory on the 11/83 is probably about as fast as the on board memory on the 11/93. As for the actual CPU, almost all M8190 quad CPU boards or KDJ11-Bx (maybe all) allow the use of PMI memory which is the primary reason the 11/83 is faster than the 11/73. The other reason is the 18 MHz clock rate on the 11/83 as opposed to the 15 MHz clock rate on the 11/73. So if anyone has a M8190 CPU with non-PMI memory and can find some PMI memory, then as long as there are ABCD slots available for all of the memory and CPU boards, the system will run much faster with PMI memory. Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.