To expand on what Sean said with some basics: Red Book CDs are 2-channel only, sampled at 44.1 kHz and use 16 bit word lengths. Some of the recent variations are multi-channel recordings, sampling rates of 48 kHz, and 96 kHz, and word lengths of up to 24 bits for PCM encoded data. For SACD, multi-channel is also possible, the sample rate is 2.811 MHz (I think) and the word length is 1 bit.