Intel Motherboard | AMD Motherboard

S/PDIF stands for Sony/Philips Digital Interface Format, the two companies being the primary designers of the S/PDIF format. S/PDIF is a collection of hardware and low-level protocol specifications for carrying digital audio signals between devices and stereo components. It is more recently part of a larger collection of standards IEC 60958 (often referred to as AES/EBU), where it is known as IEC 958 type II. S/PDIF is essentially a minor modification of the original AES/EBU standard for consumer use, providing small differences in the protocol and requiring less expensive hardware. A common use for the S/PDIF interface is to carry compressed digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a home theater receiver that supports Dolby Digital or DTS surround sound.
There are no differences in the signals transmitted over optical or coaxial S/PDIF connectors—both carry exactly the same information. Selection of one over the other rests mainly on the availability of appropriate connectors on the chosen equipment and the preference and convenience of the user. Connections longer than 6 meters or so, or those requiring tight bends, should use coaxial cable, since the high light signal attenuation of TOSLINK cables limits its effective range. On the other hand, TOSLINK cables are not susceptible to ground loops and RF interference like coaxial cables. One deciding factor for many is cost—any standard 75 ohm A/V cable can be used for coaxial connectivity, while TOSLINK requires a proprietary cable which is often sold at a high mark-up.

Read more about S/PDIF here.