This is basically the 1974 version of a DIMM. It measures 16″ by 11.5″ and holds 16 kilobytes. It’s technically 18 bits wide but only 16 were used in the PDP-11. The raised part in the middle is where the cores are actually stored. Each bit is a little ring with 3 wires running through the middle. By running current through the wires you could magnetize or demagnetize each ring. One interesting tidbit is that reading is destructive! When you read a bit you are actually demagnetizing the ring and the memory controller had to then do a write cycle to restore the bit.