'Simplest' in what sense? They certainly aren't the easiest ones to understand, with all that random control logic! The -11/04 is far easier to understand (for me, at least; YMMV). I'm pretty sure there was never a UNIBUS quad memory card from DEC. New ones (not exactly the same as the originals, but the right size in the X/Y directions, if not identical in the Z, and 110V, with the same kind of power connector) are available on eBait for around $10 each. Look for "120mm 110V fan". Noel