(MO) A plastic or glass disk coated with a compound (often TbFeCo) with special optical, magnetic and thermal properties. The disk is read by bouncing a low-intensity laser
off the disk. Originally the laser was infrared, but frequencies up to blue may be possible giving higher storage density
. The polarisation of the reflected light depends on the polarity of the stored magnetic field.
To write, a higher intensity laser heats the coating up to its Curie point, allowing its magnetisation to be altered in a way that is retained when it has cooled.
Although optical, they appear as hard drives to the operating system
and do not require a special filesystem
(they can be formatted as FAT
The initial 5.25" MO drives, introduced at the end of the 1980s, were the size of a full-height 5.25" hard drive
(like in IBM PC XT
) and the disks looked like a CD-ROM
enclosed in an old-style cartridge
In 2006, a 3.5" drive has the size of 1.44 megabyte diskette drive
with disks about the size of a regular 1.44MB floppy disc
but twice the thickness.
Storage FAQ (http://cis.ohio-state.edu/hypertext/faq/usenet/arch-storage/part1/faq.html).