Read Write Hold and Deslect 4520 D 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 4520 D" is printed on the solder side at the insertion end above the grid lettered A-Z.