If a computer uses the 16550a 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 computers that do not enable this buffer experience loss of characters at 9600 baud, and most cannot communicate at speeds higher than 9600 baud.)
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 spec-ify whether the buffer for a given port should be enabled or disabled. If the value of the setting is 1, the driver enables the FIFO buffer; otherwise, it disables the buffer. If no setting is specified, the driver will enable the buffer by default.
The virtual-communications device (VCD) does not virtualize the 16550a for non-Windows applications.