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Definition: magneto-optic disk

An earlier removable, rewritable optical disk that also used magnetic technology. Introduced in 1985, magneto-optic (MO) media and drives are no longer manufactured. Refurbished drives and media are available from MaxOptix.com.

Laser-Magnetic Writing
A laser heats the optical bit to the Curie point, and a magnet changes the bit's polarity. The laser is on one side of the platter and the magnet on the other, which requires double-sided media to be manually flipped over to access the other side.

Writing initially sets the bits to zero and then writes the data in a second pass. A single-pass LIMDOW (Light Intensity Modulated Direct OverWrite) method was later added, and many drives supported the more costly LIMDOW media.

Laser Reading
A low-power laser light is reflected from the bits, and depending on their polarity, the difference in the light's rotation is sensed. See UDO, Kerr effect and optical disc.

Two Cartridge Sizes
The 3.5" media were single sided, while the 5.25" disks were double sided. With a 50-year shelf life, up to 9.1GB of storage and capable of a million rewrites, access times in the sub-25 ms range were faster than optical-only CD/DVD media.

A Fujitsu Cartridge in 2002
Excerpted from the December 2002 issue of PC Magazine, 2.3 gigabytes was a large amount of removable storage around the turn of the century. (Image courtesy of Fujitsu and PCMag.com.)