6000 series I assume, specifically I was told these came from a prototype system (?) from the early 1970's, and were then surplused after light use. I don't have confirmation on that. They could be used in a PDP 11/45 (?), IBM 3179, and I know first-hand that they can be adapted for use in a microprocessor system as others of this same model were used in a 8008 system (I think) homebrew project or two that I have seen. Late core-era adaptable memory. If I get more info I will let you know. I still have at least one partial rack available if anyone is interested contact me directly. Bill