Correct (and your knowledge and memory is good)! Motivated by this clue, I looked in: Emerson W. Pugh, "Memories That Shaped an Industry" MIT Press, Cambridge, 1984 where the description of the invention of 3-wire core can be found on pg. 231; it was invented by a group of engineers, based on a similar idea used in Stretch. There is indeed a patent, No. 3,381,282, with six names on it. IBM must have licensed it, but there is nothing on that. I can highly recommend that book; it's in the same league as the later two books on early IBM computers from MIT Press on which he was a co-author. Noel PS: There was recent discussion here of the 8000 series; there are some details on that on pp. 189-191.