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A Magneto-optical disc and the numerous rectangles on its surface. 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 (5.25 in) and 90 mm (3.5 in) form factors exist.  The technology was introduced commercially in 1985 . 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.). Magneto optical drives are common in some countries such as Japan but have fallen into disuse in other countries like the United States.
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1 Technical aspects 2 Vendors 3 Floptical drives 4 Recent progress 5 See also 6 External links 7 References
 Technical aspects
A 130 mm 2.6GB Magneto optical disc.
A 90 mm 640MB Magneto-optical disc.
A 230 MB Fujitsu 90 mm magneto-optical disc. Initially the drives were 130 mm and had the size of full-height 130 mm hard-drives (like in IBM PC XT). 130 mm media looks similar to a CD-ROM enclosed in an old-style caddy, while 90 mm media is about the size of a regular 1.44MB floppy disk, but twice the thickness. The cases provide dust resistance, and the drives themselves have slots constructed in such a way that they always appear to be closed. The disc consists of a ferromagnetic material sealed beneath a plastic coating. There is never any physical contact during reading or recording. During reading, alaser projects a beam on the disk and according to the magnetic state of the surface, the reflected light varies due to the Magneto-optic Kerr effect. During recording, the laser power is increased so it can heat the material up to the Curie point in a single spot. This allows an electromagnet positioned on the opposite side of the disc to change the local magnetic polarization, and the polarization is retained when temperature drops. Each write cycle requires both a pass for the laser to erase the surface, and another pass for the magnet to write the information, and as a result it takes twice as long to write data as it does to read it. In 1996, a Direct Overwrite technology was introduced for 90 mm discs, to avoid the initial erase pass when writing. This requires special media.
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The NeXT computer was the first to offer this technology, but Canon eventually provi ed it to other customers. Sony Mini iscs are magneto-optical, and Sony produces many other formats of magnetooptical media. Pinnaclemicro was a major manufacturer of magneto optical drives. 3.5" drives were 128MB and 230MB. 5.25" drives produced were 650MB and 1.3GB (Sierra), 2.6GB (Vertex) and 4.6GB (Apex). The Vertex and Apex were non-ISO standard drives and used a proprietary media. Pinnaclemicro has ceased production of these products. Maxoptix is a major manufacturer of 130 mm or 5.25 magneto optical drives. Current model is T7-9100 drive which has a maximum capacity of 9.1GB and is downward read and write compatible with 5.2GB, 4.8GB, 4.1GB, 2.6GB, and 2.3GB MO disks, and read compatible with 1.3GB, 1.2GB, 650MB, and 600MB magneto-optical disks. Popular older models of 5.25 Maxoptix MO drives are the T6 Star, T6-5200 and T5-2600 MO drives. See  for more details.
Fujitsu was a major manufacturer of 90 mm magneto-optical drives, exceeding 2 GB in capacity, but they have discontinued production and sale of this product category. PDO Konica Minolta is now the only manufacturer of 90 mm 3.5" magneto-optical drives. They have a 3.5" 1.3GB USB external pocket drive available for sale in the United States and Europe. Source this drive in the United States at , and in Europe at .
[edi Flopti l dri es
Magneto-optical drives should not be confused with Floptical drives, which likewise combine ferromagnetic and optical technologies, albeit in a different manner. Flopticals are 21 megabyte 90 mm magnetic diskettes using optical tracks to increase the tracking precision of the magnetic head; from the usual 135 tracks per inch to 15,000 tracks per inch. No laser or heating was involved; a simple infrared LED was used to follow the optical tracks, while a magnetic head touched the recording surface. The drives could also read and write traditional 90 mm diskettes, although not the 2.88 megabyte variety. Flopticals were manufactured by Insite Peripherals, a company founded by Jim Burke.
 Recent progress
At the Consumer Electronics Show in January 2004, Sony revealed a 1 gigabyte capacity MiniDisc known as "Hi-MD." This sixfold increase in capacity is performed using a magneto-optical trick. To record a standard MiniDisc the writer uses an infrared laser to heat a spot of ferromagnetic material on the disc to above its Curie point, then it is magnetised by a recording head as it cools. In contrast a high capacity MiniDisc uses tracks that are one sixth of those used in standard MiniDiscs. By employing three magnetic layers, when a high capacity MiniDisc is read, the track expands to readable si e. Specifically the three layers are, from read-face to print-face: a displacement layer, a switching layer, and a memory layer. When it isn't being read, the magnetic field in the memory layer is the same as those in the displacement and switching layers. When a laser shines on the track, the switching layer, which has a lower Curie point than the other layers, demagnetises. It decouples from the displacement layer, whose "magnetic fence" around the track weakens, temporarily causing the track to swell to a readable si e. Hi-MD recorders can also double the capacity of regular minidiscs with special formatting that renders the disc unreadable (or writable) by non-HiMD minidisc recorders. As with all removable storage media, the advent of cheap CD/DVD drives and flash memory has made them largely redundant. Magneto-optical disks in particular were expensive when new, and while highly reliable, the slow writing time also was a negative factor. The magneto-optical (MO) drive is a popular way to back up files on a personal computer. As the term implies, an MO device employs both magnetic and optical technologies to obtain ultra-high data density. A typical MO cartridge is slightly larger than a conventional 3.5-inch magnetic diskette, and looks similar. But while the older type of magnetic diskette can store 1.44 megabytes (MB) of data, an MO diskette can store many times that amount, ranging from 100 MB up to several gigabytes (GB).
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An MO system achieves its high data density by using a laser and a magnetic read/write head in combination. Both the laser and the magnet are used to write data onto the diskette. The laser heats up the diskette surface so it can be easily magneti ed, and also to allow the region of magneti ation to be precisely located and confined. A less intense laser is used to read data from the diskette. Data can be erased and/or overwritten an unlimited number of times, as with a conventional3.5-inch diskette. Examples of magneto-optical drives are the Fujitsu DynaMO, a 230 MB drive used in the PowerPC Apple Powerbook, a note book computer, and the Pinnacle Micro Vertex, a 2.6 GB drive. The chief assets of MO drives include convenience, modest cost, reliability, and (for some models)widespread availability approaching industry standardi ation.The chief limitation of MO drives is that they are slower than hard disk drives, although they are usually faster than conventional 3.5-inch diskette drives.