Recording medium and signal processing unit for recording medium drive

[0043]FIG. 1 illustrates a magneto-optical disk 11 as an example of a recording medium according to the present invention. The magneto-optical disk 11 is a so-called concurrent ROM-RAM magneto-optical disk. The diameter of the magneto-optical disk 11 is set at 120 mm, for example. It should be noted that such a medium might take the shape of a card or the like in place of the shape of a disk.

[0044]FIG. 2 schematically illustrates a sectional view of the magneto-optical disk 11. The magneto-optical disk 11 includes a substrate 12 in the shape of a disk. The substrate 12 is made of a transparent material. The transparent material may be a resin material such as polycarbonate, amorphous polyolefin, or the like. Injection molding is employed to form the substrate 12. An undercoat film 14, a magnetic recording film 15, an auxiliary magnetic film 16, an overcoat film 17, a reflection film 18 and a protection film 19 are formed on the surface of the substrate 12 in this sequence. The underco