More layers than a writable DVD is capable of having yet.

Edit: I should elaborate: A DVD can have up to 4 total layers, 2 on each side. That I know of no commercial 4 layer DVDs have been issued. There may be 3 layer DVDs now, but the typical DVD is either 2 sides 1 layer each, or 2 layers on 1 side. That gives you a total of 9.4gb. A writable DVD gives you one layer, one side, for a total of 4.7gb.

http://www.vcdhelp.com should have a discussion of this in their userguide section.