The best known pin/socket I/O connector is the D Subminiature or D-Sub invented by ITT Cannon in 1952. It is still used for RS-232 serial communications for connecting analog VGA monitors and parallel port devices designed to meet IEEE 1284-A. The 'D' in the name refers to the shape of the stamped metal face that prevents the plug and socket connectors from being attached the wrong way round. It is offered in a few popular sizes with metal shells for protection from EMI/RFI.