Asus P8B-M - Manual (Page 50)

2-32 Chapter 2: Hardware information
7. Serial port connector (10-1 pin COM2)
Thess connectors are for the serial (COM) ports. Connect the serial port
module cable to one of these connectors, then install the module to a slot
opening at the back of the system chassis.
8. BMC header (BMC_FW1)
The BMC connector on the motherboard supports an ASUS ® Server
Management Board 5 Series (ASMB5).