Disk drive embedded servo system having a servo field with an

Abstract

An embedded servo system for a disk drive is disclosed. An asymmetrical position sub-field reduces the overhead of the disk position system. The sub-field includes at least two normal frame pairs and only one quadrature frame pair interleaved with one of the normal pairs to form the asymmetrical position sub-field. The prerecorded embedded servo information in each track of the disk includes a multiplicity of different length servo fields, i.e, each track includes at least two types of servo fields where the first type has a first length and the second type has a second length that is different from the first length. The length of a servo field refers to the number of prerecorded bytes in the servo field. The multiplicity of different length servo fields includes a first type having a full track address sub-field and a second type having a modulo track address sub-field in place of the full track address sub-field. In another embodiment, the multiplicity of different length servo fields includes the first and second types of servo fields and a third type of servo field. The third type of servo field includes only track following information and no track address information, i.e., the third type of servo field is a position only servo field. The servo fields of differing lengths are interleaved in each track of the disk. The servo fields are chosen to provide a high seek sampling rate in comparison to the required performance and a reduction in the servo overhead. Increased track following sampling is provided to make the read/write head less likely to move off track in response to external forces on the disk drive. Disk drives with different types of servo fields interleaved are particularly well-suited for small portable computers.