If a computer uses the 16550 Universal Asynchronous Receiver Transmitter (UART) for its communication ports, the communications driver will enable the onboard 16-byte First In, First Out (FIFO) buffer allowing Windows to perform reliable serial communications at speeds of 9600 baud and higher. (Many systems that do not enable this buffer experience loss of characters at 9600 baud, and most cannot communicate at speeds higher than this.)
Before enabling the FIFO buffer, the communications driver checks the SYSTEM.INI file to determine whether the user wants the buffers enabled. The COMxFIFO settings in the [386Enh] section of the SYSTEM.INI file specify whether the buffer for a given port should be enabled or disabled. If a setting should be enabled, the driver enables the FIFO buffer; otherwise, it disables the buffer. If no setting is specified, the driver will enable the buffer by default