What is SACD?

What does SACD stand for? And how does it differ from CD?
SACD is Super Audio Compact Disc. It uses a disc similar to the DVD in that it can be multi layered and multi sided. It can store up to 17 Gigabytes of information as compared to a CD which stores only 640 Megabytes. It also uses a completely different encoding scheme refered to as DSD. This scheme differs from traditional PCM (used on CDs and DVDs) in that it uses only one bit at very high sampling rates (something like 2.4 MegaHertz as opposed to the 44.1 KiloHertz of CD). Sony was one of the initiators of this technology and has an area on their web site dedicated to the explaination of the technology. It is:

Abstract, good response. I would like to point out that SACD is intended to be a better CD and not replace DVD. Most SACDs do not have video and the majority are stereo (like CDs). The hybrid SACDs can be played in both CD players and SACD players, and a greater number of discs and players in the future will have multichannel capability. DVDs can't be played in CD players.

Right now, many audiophiles believe that SACD is the highest quality recordings available to the public.