Read Write Hold and Deslect 4520 C system building block
Digital Equipment Corporation (DEC)
||Printed on the solder side near the insertion end (the 4 is missing)
||Stamped into the face of the aluminum frame
overall: 1/2 in x 4 1/2 in x 7 in
One one side the board is half covered in various components. "READ WRITE HOLD AND DESELECT _520 C" is printed on the solder side at the insertion end above the grid lettered A-Z.