Essential Guide to Computer Data Storage: From Floppy to DVD, The

Direct Overwrite (DOW)

Direct overwrite is an extremely important technology for the MO drives since it allows to roughly double the speed of the rewrite operation. A more traditional rewrite operation includes two steps (and two disk rotations):

• Irradiation and heating of the selected bit for overwriting to exceed the Curie temperature, forcing its coercivity to drop to zero, and then reversal in magnetic field for erasure.
• Second irradiation with magnetic field applied to write a new information into the bit.

The above process requires two passes over the same bit. The DOW technology allowed to erase and rewrite the new data in one pass.

There are two techniques used for DOW: the magnetic field modulation DOW, called (MFM-DOW), and the light ...