optical disk, any of a variety of information storage disks that are played or read using a laser. Optical disks include compact discs (CDs and CD-ROMs), laser discs (see videodisc), and digital versatile discs (or digital video discs; DVDs and DVD-ROMs). WORM [Write Once/Read Many] disks can be used to record data, but once data is recorded it cannot be altered except by obliterating the old version and storing the new version on a previously unused portion of the disk. Magneto-optical disks, such as the rewritable optical disk and the recordable disk used with the Mini Disc player, have a special layer, as of barium ferrite, that can be magnetically polarized by a recording head when heated with a laser. Data or sound may be recorded to and erased from any portion of a magneto-optical disk multiple times.

The Stacked Volumetric Optical Disk (or SVOD) is an optical disk format developed by Hitachi/Maxell, which uses an array of wafer-thin optical disks to allow data storage of around 1TB.

Each "wafer" (a thin polycarbonate disk) holds around 9.4GB of information, and the wafers are stacked in layers of 100 or so, giving overall data storage increase of 100x or more.

SVOD will likely be a candidate, along with HVDs, to be the next-generation optical disk standard.

External links

• Hitachi Maxell develops wafer-thin storage disc details and interview from IDG News Service (Oct 4, 2006)
• Maxell details in Japanese language (Apr 19, 2006)
• NikkeiBP some details in English (Apr 20, 2006)