PDP-11/23 PLUS commercial instruction set (CIS)

Jerome Fine replies: I have never heard of any other "microms" for the 11/23 or the 11/24, but that does not mean that there are none. However, none of the manuals I have on the 11/23 dual (M8186) or the 11/23 quad (M8189) modules have ever mentioned any. So I would say it is doubtful. If there are any, I suspect they would be a private development and that seems even more doubtful considering the expense. On one point I am requesting some clarification. I have in my hands both an M8186 and an M8189. There are five pair of sockets for five microms. Right now, the CPU, MMU and FP microms are present. In the past, I have found that the order does not seem to be important, but I have not run an 11/23 (either one) lately and can't remember for sure. In any case, that leaves just two empty pair of sockets (20 pins each) which I presume would be filled by ONE CIS microm which is double width and would use one side of pair number 4 and the opposite side of pair number 5. Is this interpretation correct? I did not quite understand what you stated above since 5+6 does not seem to exist on either 11/23. I guess that if either the MMU or the FP were not present, the CIS microm could be moved down, but I presume that when inserting the CIS microm, the port side should always go into a port set and the starboard side should always go into a starboard set, just as with the CPU, MMU and FP microms. Based on the geometry, it seems impossible to insert a rom into the wrong pair because the spacing makes that impossible although it is obviously possible to reverse the direction of the rom and put it in backwards. Of course, this all assumes that a CIS microm is available! I have heard that the 11/44 has CIS and that the block move instruction is often used instead of a loop. Sincerely yours, Jerome Fine