Jerome Fine replies: YES!! You are correct. Many years ago, I finally acquired a M8190-AE and some PMI memory. I don't know how many are interested, but I found the following: Approximate speed increase from M8190-AB (KDJ11-BB) with normal DEC memory (obviously below the CPU) vs M8190-AE (KDJ11-BF) with DEC PMI memory above the CPU was about 33%. An assembly which took about 4.5 minutes was reduced to about 3 minutes. I can't recall the exact numbers or exactly what I tried, but the test with the M8190-AB and the PMI memory above the CPU took about 23% less time than 4.5 minutes. I then tried the M8190-AE and normal DEC memory below the CPU and that took about 10% less time than 4.5 minutes. When the PMI memory was below the M8190-AE, that also took about 10% less than the 4.5 minutes. Based on my observations, I can suggest that the use of PMI memory is the major reason for the speed improvement, NOT the change of the crystal from 15 MHz to 18 MHz when the switch was made from the M8190-AB to the M8190-AE. I am not sure if this conclusion agrees or disagrees with what you stated above. However, it is what I found during my rather limited test. I have heard from others (I think that Megan Gentry once stated that she did this as well, but it might have been with the M8190-AE board) who also were able to effect a substantial speed improvement just using PMI memory above the CPU board. Of course, when DEC first sold PMI memory, it was EXTREMELY expensive compared to normal memory which was VERY expensive compared to memory for a PC. Later, I was able to find PMI memory at a price below that for normal memory since most people at the time thought that PMI memory could ONLY be used with an M8190-AE board. Now all DEC memory seems to be expensive again and PMI memory is also expensive. The first time I do also. But I still get a bigger thrill Enhancing one of the utilities or adding Y10K to RT-11 is also the same sort of challenge from my point of view that you probably receive from fixing an M8190-AE board. I realize that the majority on this classiccmp list enjoy the hardware more than the software, but I hope I am not completely alone! And then there is the program to locate the PRIME numbers from the range of numbers from 1 to 4,000,000,000. I have not worked on that one for a while. I want to see how Ersatz-11 can help by improving access to memory for FORTRAN VIRTUAL statements. I need about 500 Kbytes and the MMU makes things very slow. With direct access to PC memory and a system 100 times as fast as a PDP-11/93, the system should be a lot faster. I may be able to locate all the PRIME numbers from the range of numbers 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.