1. Field of the Invention
The present invention relates to a discrete track magnetic recording medium having one surface or both surfaces of a disk-shaped substrate thereof formed with an annular data-recording area having a plurality of tracks separated from each other by concentric separating grooves or a spiral separating groove.
2. Description of the Related Art
Today, as a recording medium on which high density recording can be performed, there has been developed a discrete track magnetic recording medium (e.g. a magnetic recording medium disclosed in Japanese Laid-Open Patent Publication No.H04-310621. This magnetic recording medium has a disk-shaped substrate formed with a data-recording area having a plurality of data-recording tracks (hereinafter simply referred to as “tracks”) magnetically separated from each other by a plurality of concentric grooves. This kind of discrete track magnetic recording medium (hereinafter also referred to as the “discrete track medium”) is mounted e.g. on an HDD (Hard Disk Drive), and various record data are magnetically recorded thereon via a magnetic head for use in recording or reproduction (hereinafter also referred to as the “magnetic head”). In this case, in the discrete track medium, grooves are provided between tracks to thereby prevent undesired increase in effective recording track width, due to the leakage field from the magnetic head. Further, the discrete track medium has the advantage of reduced occurrences of recording of record data on adjacent tracks and reproduction of record data recorded on adjacent tracks (cross-talk). This makes it possible to reduce the pitch at which tracks are to be formed (hereinafter referred to as the “track pitch”), whereby record data can be recorded with high density.
On the other hand, in an HDD having this kind of discrete track medium (e.g. a discrete track medium 51 shown in FIG. 7) mounted thereon, during recording or reproducing of record data, a motor causes the discrete track medium 51 to be rotated at high speed. Further, as shown in FIG. 8, a servo control mechanism, for example, moves (performs servo control of) a magnetic head 71 along the radius of the discrete track medium 51 such that the central portion of the magnetic head 71 is placed on any one of tracks 62 in a data-recording area 53 formed on a disk-shaped substrate 52. In this case, an air current is generated between the magnetic head 71 and the discrete track medium 51 (data-recording area 53) by the high-speed rotation of the discrete track medium 51, which causes the magnetic head 71 to fly by a lift generated by the air current. As a result, it is possible to move (rotate) the discrete track medium 51 and the magnetic head 71 such that they are prevented from contacting each other.
However, from the study of the proposed discrete track medium 51, the present inventors found out the following points for improvement: In the discrete track medium 51 of the above-mentioned kind, as shown in FIG. 7, an outer area 54 and an inner area 55, neither of which has any grooves 61 (see FIG. 8) formed therein, exist outward and inward of the data-recording area 53 on the disk-shaped substrate 52, and hence inconveniences are caused by the areas 54 and 55. More specifically, as shown in FIG. 9, when data is recorded on or reproduced from a track 62A at the outermost location in the data-recording area 53, it is required to place the central portion of the magnetic head 71 on the track 62A, so that an outer portion of the magnetic head 71, outward of the central portion of the same, protrudes into a region above the outer area 54.
In this case, as shown in FIG. 9, the volume of a space defined between the outer portion of the magnetic head 71 and the outer area 54 is smaller than the volume of a space defined between the inner portion of the magnetic head 71 and the data-recording area 53, by an amount corresponding to grooves 61 that are not formed in the outer area 54. Now, the aforementioned lift applied to the magnetic head 71 tends to become larger, as the amount of air between the magnetic head 71 and the discrete track medium 51 is smaller, that is, the volume of a space defined therebetween is smaller. Therefore, as shown in FIG. 9, in a state where the magnetic head 71 is parallel to the surface of the discrete track medium 51, a lift F5 applied to the outer portion of the magnetic head 71 becomes larger than a lift F6 applied to the inner portion of the magnetic head 71. As a result, as shown in FIG. 10, the magnetic head 71 is inclined until the volume of the space defined between the outer portion of the magnetic head 71 and the outer area 54 becomes equal to the volume of the space defined between the inner portion of the magnetic head 71 and the data-recording area 53 (i.e. until the lift F5 becomes equal to the lift F6). Therefore, as shown in FIG. 10, the discrete track medium 51 suffers from the problem that the magnetic head 71 can contact the surface of the discrete track medium 51 (data-recording area 53) due to the thus caused inclination of the magnetic head 71.