3F8/IRQ4 (COM1): Sets the serial port to the I/O address and IRQ normally used by COM1. This is usually the default for the first serial port.
2F8/IRQ3 (COM2): Sets the serial port to the I/O address and IRQ normally used by COM2. This is usually the default for the second serial port.
3E8/IRQ4 (COM3): Sets the serial port to the I/O address and IRQ normally used by COM3.
2E8/IRQ3 (COM4): Sets the serial port to the I/O address and IRQ normally used by COM4.