光ディスク
An Ultra Density Optical disc or UDO is a 133.35 mm (5.25") ISO cartridge optical disc which can store up to 30 GB of data. The second generation UDO2 media was introduced in April 2007 and has a capacity of up to 80 GB. Utilising a design based on a Magneto-optical disc, but using Phase Change technology combined with a blue violet laser, a UDO/UDO2 disc can store substantially more data than a magneto-optical disc or MO, because of the shorter wavelength (405 nm) of the blue-violet laser employed. MOs use a 650 nm-wavelength red laser. Because its beam width is shorter when burning to a disc than a red-laser for MO, a blue-violet laser allows more information to be stored digitally in the same amount of space.