BD-J (or BD Java) is the name given to the Java-based software that will be included on BD-ROM discs and all Blu-Ray Disc players. This will help provide the Blu-ray menus and many other features. On DVDs, menu's are made up of segments of MPEG video, or still frames. BD-J and the interactivity layer used by HD DVD, iHD, are far more advanced and will offer greater features than DVD. The Blu-ray group is using a specification from Europe called JEM.
The rivals of Blu-ray Disc have attacked the groups use of JEM for interactivity features because the specification has a very high number of instructions that will apparently make it very tough for manufacturers to ensure that all devices will function properly. HP urged the Blu-ray Disc Association to rethink the use of Java and consider using the DHTML based iHD instead. This would make it cheaper for PC manufacturers as iHD is an integral part of Microsoft's upcoming Windows Vista operating system.