ISO 7816-4

This international standard defines both a communication scheme and a command set. The communication scheme is made of APDUs. The command set assumes that the card is structured the same way as a computer disk drive: directories and files could be selected (SELECT instruction) and accessed for reading or writing (READ BINARY, UPDATE BINARY instructions). More than 40 instructions are defined by the standard, but most cards implement only a small subset, and often add their own (vendor-specific) instructions.