Patent ID: 7388817
Filing Date: 2008-06-17
Classification: G11B

Abstract:
1. A method of measuring a head gap length of a composite head, for use in a disk storage device with the composite head, the composite head including a read head used to read data from a disk, and a write head separate from the read head in a circumferential direction of the disk and used to write data to the disk, a disk format being applied to the disk, the disk format being constructed such that servo regions which record servo data are dispersively arranged at regular intervals in the circumferential direction of the disk, a region between a pair of adjacent ones of the servo regions being assigned as a data region in which a plurality of data sectors are arranged, the method comprising: writing, in accordance with a write gate signal generated by a write gate generator, to the disk, sector data containing preamble data, a sync mark and user data, using the write head of the composite head, the write gate signal indicating a period in which sector data is written to the disk; reading, in accordance with a read gate signal generated by a read gate generator, the sector data from the disk, using the read head of the composite head, the read gate signal indicating a period in which the sector data is read from the disk; detecting the sync mark in the sector data read by the read head, using a read circuit; delaying, in a particular mode for measurement of the head gap length of the composite head, timing of generation of the write gate signal by the write gate generator relative to reference timing by a period corresponding to an allowable maximum head gap length, the reference timing being determined from a time corresponding to an end of one of the servo regions, the one servo region being located just before the data region of the disk into which the sector data is written; measuring, in the particular mode, a data length of the preamble data as a read preamble data length, the read preamble data length corresponding to a period ranging from a time at which the read gate signal is asserted, to a time at which the read circuit detects the sync mark; determining, in the particular mode, the head gap length of the composite head based on the measured read preamble data length, a write preamble data length, a write path delay and a read path delay, the write preamble data length being a data length of the preamble data contained in the sector data to be written to the disk, the write path delay being a data length corresponding to a signal delay time in the write circuit, the read path delay being a data length corresponding to a signal delay time in the read circuit; storing, into a nonvolatile storage, head gap information indicating the determined head gap length; shortening, before writing sector data to the disk in a normal mode, the data length of the preamble data to be contained in the sector data by a data length corresponding to the head gap length indicated by the head gap length information stored in the nonvolatile storage; and delaying, in the normal mode, timing of generation of the write gate signal by the write gate generator by a period corresponding to the head gap length indicated by the head gap length information stored in the nonvolatile storage.