The PlayStation Portable (PSP) is making the reduced size optical media popular, and until now Sony has kept the format closed and stricly for them selves. But now it seems that the winds of change are blowing, and the format might see wider use, and different applications. Sony has proposed to keep the PSP implementation of UMD closed, but to release the format for audio and video applications.
UMDs are 60-millimeter optical discs in protective cases that have a data storage capacity of 1.8GB. They were developed by Sony for use in the PSP, but plans already reach beyond gaming. Specifications for versions of UMD holding games, movies and music have all been drawn up. However, at present the only commercial UMD content on the market is the handful of games available for the PSP.
... Sony will give companies access to the movie and music variants of the technology so that they might produce multimedia players that support UMDSource: Computerworld.com