Jerome Fine replies: While I have heard of a PDP-11/23 PLUS, I don't think that "PLUS" was ever applied to the PDP-11/73 boards. "PLUS" could mean either the ability to address all 4 MBytes of memory with the dual M8186 boards (I understand that the original M8186 boards were able to address only 256 KBytes) or that the quad M8189 board was being used. As for the PDP-11/73 boards, I had heard that some did have the 18 Mhz crystal, but that might also have been done privately. Megan Gentry just mentioned that she changed the crystal on her PDP-11/83 board to 20 MHz and it ran correctly. This answer was with respect to the boot ROMs. I have both a KDJ11-BB (M8190-AB) and a KDJ11-BF (M8190-AE). Aside from the 15 MHz vs the 18 MHz crystal, the fact that the latter also had the FPU chip was standard with the KDJ11-BF. But the rev number of the J11 chip on the KDJ11-AB is 04 and the EPROMs are version 395E5 / 396E5 which can also be the EPROMs for the KDJ11-BF. However, I understand that the J11 rev number when an 18 MHz crystal is being used must be at least 08 and maybe 09. So the dialogue for the PDP-11/73 and the PDP-11/83 can be identical - it just depends on which version of the EPROMs is being used. I agree, however, that the early EPROMs would not have been used with a KDJ11-AE board, but the EPROMs on an early KDJ11-AB could easily have been updated along with the J11 rev number. All this discussion seems to point out that the PDP-11/73, PDP-11/83 and PDP-11/93 boards were not identical nor did they use the same J11 CPU chip all the time, although the last 09 rev CPU chip that was used with the PDP-11/93 would probably work with all of the others, just NOT the other way around with the early 04 rev CPU chips. The really sad part of the whole PDP-11 situation was that DEC upper management decided early in the 1980s to attempt to kill the PDP-11 as far as can be understood IF DEC had decided to split into two completely separate and independent companies in 1985 - PDP-11 & VAX, we might still be seeing both being built along with the Alpha. The competition from a strong PDP-11 (even though the target market was different by 1990) might have been sufficient to keep both the PDP-11 and the VAX alive since both companies might have actually started to advertise to build market share. And with the advent of the Alpha and another separate company, that market might also have needed advertising. While a 16 bit (64 KByte) address space is extremely limiting, for programs overlays can normally (I agree NOT always) substitute. For DATA, FORTRAN was able to solve that problem with VIRTUAL. For the target market of the PDP-11 where they are still being used, such a CPU is still satisfactory. And with Ersatz-11 showing that a much faster CPU (50 times the speed of the 11/93) keeps an existing system competitive, it would have been reasonable to assume that if the Alpha could manage to switch to a PCI bus, then likewise it seems very possible to me that the PDP-11 could have done so as well. even a 32 bit bus could have kept the PDP-11 somewhat competitive if there seemed to be sufficient interest. ALL GONE!!!!!!!! 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.