TDK Develops 320GB Optical Disc

The 12-centimeter disc has 10 recording layers, each of which can store 32 Gigabytes.

In comparison a Blu-ray Disc can hold 25GB on each layer, and a dual-layer disc is the highest capacity generally available at present.

Source:
http://www.pcworld.com/businesscenter/article/173453/tdk_develops_320gb_optical_disc.html