Magneto-optical drive

A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. Both 130 mm and 90 mm form factors exist. The technology was introduced at the end of the 1980s. Although optical, they appear as hard disk drives to the operating system and do not require a special filesystem (they can be formatted as FAT, HPFS, NTFS, etc.).

Ultra Density Optical (UDO) is an optical disc format designed for high-density storage of high-definition video and dataAn Ultra Density Optical disc or UDO is a 133.35 mm (5.25") ISO cartridge optical disc which can store up to 60 GB of data.Utilising a design based on a Magneto-optical disc, but using Phase Change technology combined with a blue violet laser, a UDO 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.

Current generations of UDO store up to 60 GB, and a 120 GB version of UDO is in development and is expected to arrive in 2007 and after, though up to 500 GB has been speculated as a possibility for UDO.[1] According to Plasmon, desktop UDO drives are priced at around US $3200. A 30GB UDO Write Once is US $60

Rewritable

The UDO Rewritable format uses a specially formulated Phase Change recording surface that allows recorded data to be deleted and modified. In practice, UDO Rewritable media operates like a standard magnetic disc. Files can be written, erased and rewritten, dynamically reallocating disc capacity. Rewritable media is typically used in archive applications where the stability and longevity of optical media is important, but the archive records change on a relatively frequent or discretionary basis. Rewritable media is typically used in archive environments where data needs to be deleted or media capacity re-used.


True write once

The UDO True Write Once format uses a different phase change recording surface than the Rewritable media. Unlike Rewritable media, the write once recording surface cannot be erased or altered, making Write Once the most stable in terms of data integrity, because the physical record is kept authentic. This level of data integrity is not usually matched by other magnetic disc or tape technologies using normal write once emulation. Write Once has been used successfully in high data integrity environments such as banks and financial institutions with similar magneto-optical discs. Its advantages are media longevity which reduces the cost and frequency of migration, and data authenticity. Common uses of True Write Once media include medical, financial, industrial and applications that have long or indefinite record retention periods with a need for unquestioned record authenticity.


The table below summarizes the differences between conventional Magneto-Optical specifications and those of the enhanced Ultra Density Optical disc
.Disc 5.25-inch UDO Rewriteable 5.25-inch UDO Write Once 5.25-inch MO system (9.1 GB)
Disc diameter 130 mm 130 mm 130 mm
Disc thickness 2.4 mm 2.4 mm 2.4 mm
Cartridge size Same as ISO 130 mm (135 x 153 x 11 mm) Same as ISO 130 mm (135 x 153 x 11 mm) ISO 130 mm (135 x 153 x 11 mm)
Number of physical tracks 96,964 96,964 49,728
Sector size 8 kB 8 kB 4 kB
Number of sectors 2,504,407 2,504,407 1,118,880
Data area 29.0-61.0 mm 29.0-61.0 mm 29.7-62.5 mm
Laser wavelength Violet (405 nm) Violet (405 nm) 660 nm
Objective lens (NA) 0.85 0.85 0.575
Recording layer Phase change Phase change Magneto-optical
Recording format Land & groove Land & groove Land & groove
Recording side Both sides Both sides Both sides
Track pitch 0.33 µm 0.33 µm 0.65 µm
Minimum bit length 0.13 µm 0.13 µm 0.3 µm
Recording density 15.0 Gb/in² 15.0 Gb/in² 3.3 Gb/in²
Transfer rate 4-8 MB/s 4-8 MB/s 3-6 MB/s
Error correction LDC LDC LDC
Modulation RLL (1,7) RLL (1,7) RLL (1,7)