Optical Drive Audio In Connector (4-Pin Cd); Digital Audio Connector (4-1 Pin Spdif_Out) - Asus M4A78-HTPC User Manual

8.

Optical drive audio in connector (4-pin CD)

This connector allows you to receive stereo audio input from sound sources such as a
CD-ROM, TV tuner, or MPEG card.
9.

Digital audio connector (4-1 pin SPDIF_OUT)

This connector is for an additional Sony/Philips Digital Interface (S/PDIF) ports.
The S/PDIF module is purchased separately.
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