Disk Properties

Significant improvements over past music storage formats can be explored by looking at the minidisc cassette. The diagram on the left shows an explodeded view of the cassette. The disc itself is fairly similar to a compact

disc, the major improvement being the housing that protects it from the same damage susceptible to the unshielded CD.

The most interesting part of the minidisc, however, is its recordable layer sandwiched in the plastics of the disc. This layer is a Terbium-Iron-Cobalt-Chromium composite and was chosen for several reasons. Primarily, the composites magnetic coercivity at room temperature is very high. Magnetic coercivity is the measure of a materials resistance to magnetic induction. For example, a VHS tape has a magnetic coercivity of 760

Diagram From:www.minidisc.org/ieee_paper.html
Oersteds (fairly low), while a minidisc has a value of 5600 Oersteds. So it is much more difficult to magnetically erase a minidisc than a VHS tape. This recording layer also has a Curie point that can easily be achieved by the low power laser used in the minidisc system. To learn more about the Curie point, please visit the laser optics section of this site. Depicted below are the Tb-Fe-Co-Cr composites and pre recorded and recorded formats.

This cross-section depicts the various layers of the minidisc. The layer 2nd from the bottom is the Terbium-Iron-Cobalt-Chromium recording layer.

Diagram From: members.rol.ch/ruby/sprinterx.html

 

This is a pre-recorded stamped disc layer. The pits are the means for storing data in this system. Since this layer won't be used for magnetic recording, it is made from a much simpler steel. Picture From: www.minidisc.org/ieee_paper.html
This is a recordable layer of Tb-Fe-Co-Cr that can be recorded on up to a million times. Magnetized data is stored inbetween the grooves. Picture From: www.minidisc.org/ieee_paper.html