Dual D.C. Sense Amplifier 4551B system building block
Digital Equipment Corporation (DEC)
Printed on the solder side of the module at the insertion end
Stamped into the face of the aluminum frame
Stamped into the side of the aluminum frame
The module consists of a board with various active and passive components surrounded by an aluminum frame and a 22 pin male connector. On the solder side there is a lettered grid running down the side, which reads A-Z.