Asus P9X79 LE - Manual (Page 44)

2-26 Chapter 2: Hardware information
Chapter 2
6. 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.
7. Digital audio connector (4-1 pin SPDIF_OUT)
This connector is for an additional Sony/Philips Digital Interface (S/PDIF) port(s).
Connect the S/PDIF Out module cable to this connector, then install the module to a
slot opening at the back of the system chassis.
The S/PDIF module is purchased separately.