1. Field of the Invention
The present invention relates generally to an information storage apparatus employing an embedded servo scheme for recording servo information and user data into a recording face of a storage medium and to a control method and program for the information storage apparatus, and more particularly, to an information storage apparatus provided with a self-servo writing feature for writing servo information into an unrecorded disk medium by the apparatus itself and to a control method and program for the same.
2. Description of the Related Art
Conventionally, the embedded servo scheme for recording servo information together with user data onto a recording face of a magnetic disk provided to a magnetic disk apparatus records servo frames as servo information for each predetermined angle in the direction along the circumference using a clock at the same frequency regardless of the differences in head, cylinder and sector. Similarly, even in a magnetic disk apparatus that divides a magnetic recording face of a magnetic disk into a plurality of zones in the direction of the radius, servo frames are recorded using a clock at a frequency determined for each zone regardless of the differences in head, cylinder and sector. On the other hand, the recording of servo frames onto the magnetic disk is executed using a dedicated servo track writer equipment during a manufacturing process of the disk apparatus. That is, a disk assembly is mounted on a bed of a servo track writer and the servo frames are written being synchronized with the clock while a high precision distance measurement is being executed from the exterior using a laser beam and a head is being moved for each track as unit one after another. Because the writing of the servo frames by the servo track writer needs dedicated manufacturing equipment and increases the cost of manufacturing, a magnetic disk apparatus has been also proposed that is provided with a self-servo writing function for recording servo frames on an unrecorded magnetic disk by the magnetic disk apparatus itself.
However, in the conventional magnetic disk apparatus that records servo frames at a constant recording density, the servo frames are written at a clock frequency of the same frequency regardless of the difference in head, cylinder and sector. Therefore, from the viewpoint of the recording density, the recording density becomes lower in the outer portion and higher in the inner portion. In addition, because a clock frequency obtained by compromising those two (2) densities is selected in the designing stage, the clock frequency is not always an optimal recording frequency for the inner and outer portions and this is one of the factors that degrades the signal quality and prevent increase of the recording density. Furthermore, from the viewpoint of a head, the optimal recording density, i.e., the balance between a track density TPi (Track per inch) and a linear density Bpi (BiTPer inch) is different for each head due to the dispersion in size and arrangement of writing cores and reading cores. However, a constant recording density, i. e., a track pitch and a recording frequency, that satisfy the lower limit of the performance of a head is determined in the designing stage and even a high performance head can only be used for the recording density at the lower limit of the performance thereof. Therefore, a problem arises that the recording density is degraded by the extent of limitation.