Exactly what kind of SPDIF-out connector is it?

I recently purchased a Dimension 4600C with Windows Media Center.

The computer has what it describes as a SPDIF-out connector to send 5.1 digital audio to a modern receiver unit or other digital audio device.

I'm learning that "SPDIF" is a generic description for a number of kinds of digital audio connectors. Exactly what kind of connector is this on the 4600C? Is it an optical, i.e. "Toslink" connector, or a digital coaxial connector? How many lines? Four?

Nowhere can I find any documentation that answers this. Forgive my ignorance, but I can't tell just by looking at it. I think it's a 4-line optical connector, but I'm too unfamiliar with this new connector to be sure....