RCA analog is not digial...hence the analog. Also, RCA is only 2 channels (in general, at least. You can have 5.1 over RCA...it just takes a lot of cables.)
SPDIF is a type of format/interface for digital audio. It does not specify what kind of cable to use. Traditionally, SPDIF is done over a "coax" cable, which simply means that two wires carry the same axis, hence co-axial or coax. Really, though SPDIF signals can be sent over any type of cable that has two leads, but the coax cables are better, as the main lead is shielded be the second. Additionally, SPDIF can be sent over optical cables, which use light to transmit data instead of electricity. Your notebook will probably sport a non-optical SPDIF interface if indeed it does...