Asus Motherboard P5B-E - Manual (Page 58)

2-34 Chapter 2: Hardware information
P5B-E
®
PIN 1
COM1
P5B-E COM port connector
13. Serial port connector (10-1 pin COM1)
This connector is for a serial (COM) port. Connect the serial port module
cable to this connector, then install the module to a slot opening at the back
of the system chassis.
The serial port module is purchased separately.