Q: What are hybrid discs?
A: Manufacturers are experimenting with combining multiple physical formats in a single multilayer disc (BD Hybrid). Theoretically, a BD Hybrid disc could contain one or two BD layers (BD-ROM/R/RE) as well as one CD (CD-ROM/DA/R/RW) and/or one or two DVD layers (DVD-ROM/±R/±RW/RAM). Such combinations are possible because each format shares many physical characteristics (radius, thickness, spiral and rotational directions, etc.) but with, however, important differences (data layers residing at different depths, written and read using different wavelength lasers, etc.). Realistically speaking, it's unclear if hybrid discs can be cost effectively mass-produced (manufacturing challenges, multiple format patent royalties, etc.) and even if there is sufficient market need or interest to warrant their development and introduction.