As stated this is a 128k word mos memory board for the 8/a processor. On its own it would only present as a 32k board. To make it work as a 128k you also need to have a M8416 board which drives the additional address lines. And not all 8/a chassis had support for this. All 4 of my backplanes have a label indicating KT8A support. I am guessing that originally the additional address lines were not connected across the backplane on the 6th connector. My card does have some bad bits and one of these days I will get around to replacing some chips. This is probably why I was able to get it not paired with the fancy MMU card. I have an M8417 but have been unable to find an M8416 at a price I was willing to pay. Apparently there are still a few 8/a's with these cards in service in Genrad testers and that makes the cards still valuable. There is info on it in the PDP 8/a PDF's on bitsavers. I think there was a TSS8 variant that used it as a fast swap but I don't know of anything else Best Wishes! On Fri, Aug 24, 2018 at 5:38 AM, allison via cctalk <cctalk at classiccmp.org> wrote: -- Doug Ingraham PDP-8 SN 1175 Assorted 8/a chassis DECSet 8000 (It is a blue PDP 8/e okay?)