The OUT instruction transfers a data byte or data word from the register (AL, AX, or EAX) given as the second operand to the output port numbered by the first operand. Output to any port from 0 to 65535 is performed by placing the port number in the DX register and then using an OUT instruction with the DX register as the first operand. If the instruction contains an eight-bit port ID, that value is zero-extended to 16-bits.