A system and method of reliable and efficient data transfer over serial port are disclosed. In one embodiment, a method of communicating data to a headless system over a communications medium includes transmitting data over the communications medium, ceasing transmitting data over communications medium in response to detecting a change in a status of a pin (e.g., a pin of a Modem Status Register, a Clear to Send, a 5th bit of the Modem Status Register, etc.) on the communications medium, and repeating the transmitting data over the communications medium in response to receiving a request to resend the data. The method may include transmitting a size of the data (e.g., a 2 byte value) over the serial port.