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Optical Drives: How They Work (Page 4/6)

Posted: May 13, 2000
Written by: Tuan "Solace" Nguyen

MO's Continued...

Below is a diagram of how a MO disc is recorded.

MO write function

When the temperature of that area is cooled down to room temperature, the magnetic elements can no longer change polarity. Because the written magnetic polarity is locked, the disk is not susceptible to magnetic fields as regular magnetic media are.

To read data from the disk, a laser is used at a low power which does not heat the disk. Depending on the recorded magnetic polarity, the polarity of the laser light reflected from the disk is rotated a few degrees either way (1 or 0). This rotation of the laser is called the "Kerr" effect. The driveís photo sensor detects this, and determines whether a 0 or 1 was read.

MO read function

Recording a MO disc does not utilize the changing dark and light reflections found in CD, CD-R and CD-RW. Instead, the recording changes the polarity (the direction in either way, representing a 1 or 0) of the reflected light. Polarizing filters are used to detect the difference and read out the north-south and south-north spots on the disc.

You may be asking "what about MiniDiscs??" Well, MDís are just MO discs. Currently, Sony has a 3.5" MO disc that can store about 1.3GB. Iím not sure if it's available yet. But be on the lookout for the news.

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