Etched on the edge of the component side of the board in solder. This number is also found on the solder side.
Etched on the edge of the component side of the board in solder
In white ink on the solder side of the board at extraction end
overall: 1/2 in x 4 11/16 in x 6 3/4 in
This 80-0021 HEX I/O circuit board is a two sided circuit board with two rows of ribbon cable connectors at the extraction end. There are three rows of integrated circuits, the largest of which are socketted. Near the extraction handle there is a module with six LED's.