Dynamic magnetic information storage or retrieval – General processing of a digital signal – Address coding
Reexamination Certificate
1998-09-15
2001-09-11
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Address coding
C360S040000, C360S077080
Reexamination Certificate
active
06288861
ABSTRACT:
TECHNICAL FIELD
This invention relates to disk drives that store recorded digital data, and in particular to disk drives that use servo sectors for maintaining the recording heads on the data tracks during read and write operations.
BACKGROUND OF THE INVENTION
Magnetic recording disk drives incorporate stacked, commonly-rotated rigid magnetic recording disks that are used for storage of user data. The data is recorded in radially-spaced data tracks on the surfaces of the disks. Recording heads are moved by an actuator in a generally radial path toward and away from the center of rotation of the disks to read and write data on the disks. Typically, a single recording head, which may be an inductive read/write head or an inductive write head in combination with a magnetoresistive read head, is associated with a corresponding magnetic recording surface of each disk.
It is necessary to know the precise radial and circumferential location of the recording heads relative to their associated disk surfaces. Radial position information is recorded on the disk as servo information and is used to locate the heads to the desired data tracks and maintain the heads over the desired data tracks during read and write operations. Circumferential position information is used to identify the start of different data fields located around the tracks. In conventional fixed-block architecture disk drives, the data is located in fixed bit length angular data sectors and the servo information is located in angularly-spaced servo sectors that are interspersed among the data sectors. This type of disk drive is referred to as a sector servo or embedded servo disk drive.
In most disk drives, it is important to accurately determine the servo sector number (SSN). This is especially true for disk drives using a headerless architecture, where there are no identification (ID) fields to locate the data sectors and the data sector numbers are derived from the SSNs. In some disk drive servo systems, the servo controller uses knowledge of the SSN to compensate for effects such as repeatable runout, which is a predictable head position error caused by the disk being not precisely centered over the axis of rotation of the spindle motor. In many disk drives, it is beneficial for the drive to determine the SSN as quickly as possible following a head switch, to speed read and write operations.
Accurate and rapid determination of SSNs is also especially important in disk drives used in portable or laptop computers that use idle modes to reduce power consumption. A typical idle mode will turn off power to the read, write and servo electronics, but keep the disk spinning. This provides for a significant power saving, but suffers from a recovery delay in returning to the fully operational (active) state. In a headerless drive, data read or write operations require knowledge of the SSN. Acquiring the SSN quickly can significantly reduce the recovery delay. Improving the recovery latency will provide additional opportunities for reducing drive power consumption using one or more of these idle modes.
In the prior art, the SSN is determined using any of a number of methods. The most common methods used are encoding an index mark on the track, and counting the SSNs from the index mark; and recording the SSN within the servo sector and then reading the SSN. Variations include combinations of these techniques, where both an index mark and some portion of the SSN are encoded within the servo sectors. However, all of these methods are susceptible to errors in the servo sectors, compromising reliability. Errors in the index sector may result in the loss of index, and errors in other sectors may cause loss of the associated SSN. The index plus count method suffers from a large latency when initially acquiring the SSN, since it must make a determination of the index location. Recording the SSN within the servo sectors reduces the disk drive's data storage capacity due to the overhead of the increased number of bits in the servo sector.
What is needed is a disk drive that can accurately and rapidly identify the servo sectors without reducing the data storage capacity.
SUMMARY OF THE INVENTION
In the present invention the SSNs are not recorded on the disk but are encoded in a manner that greatly enhances reliability of decoding the SSNs without impacting the data storage capacity of the disk. The SSNs are encoded through the use of multiple servo sector types that are arranged in a specific sequence around the data tracks. In the preferred embodiment the different servo sector types are identified by unique types of servo timing marks (STMs), which are used to locate the servo sectors. The SSNs that are used to identify the servo sectors on the track form a set or code of m fixed patterns n-bits in length. A SSN is determined when the STM types read from n sequential servo sectors correspond to one of the m fixed SSN pattems. A set or code of m servo sectors, where each servo sector is identified by a unique SSN pattern having length n, is denoted as an (m,n,d) code, where d is referred to as the sliding distance or the minimum Hamming distance of the code. The Hamming distance between two patterns refers to the number of locations that are different between the two pattems. The evaluation of a pattern of sequential STM types as the head reads successive servo sectors begins with serial bits being converted to parallel bytes. An n-bit SSN shift register is used for storing a pattern of n bits in length. Each shift creates a new pattern whose Hamming distance is compared with each of the known predetermined m SSN pattems. Determination of an SSN pattern, and thus identification of a servo sector, occurs when the input pattern either matches or where the Hamming distance is sufficiently close to one of the m SSN pattems.
The invention is not limited to servo sector number encoding and decoding in a magnetic recording disk drive, but is more broadly applicable to a wide range of systems for determining data packet identification numbers in a sequence of data packets in a cyclic manner. For example, in an optical or magnetic recording disk or tape drive that uses header fields in the recording media, the user data sectors may be thought of as the data packets and their numbers encoded and decoded in the manner according to the present invention. Similarly, a data communication stream may be comprised of a set of data packets transmitted in sequence, with unique packet type values encoded in each packet, and the sequence of packet type values used to determine the packet numbers.
REFERENCES:
patent: 4669004 (1987-05-01), Moon et al.
patent: 5544135 (1996-08-01), Akin, Jr. et al.
patent: 5596460 (1997-01-01), Greenberg et al.
patent: 5615190 (1997-03-01), Best et al.
patent: 5737142 (1998-04-01), Zook
patent: 5757567 (1998-05-01), Hetzler et al.
patent: 5768044 (1998-06-01), Hetzler et al.
patent: 5852523 (1998-12-01), Jung
patent: 6005727 (1999-12-01), Behrens et al.
Conway et al., “Redundant Index Code for Disk File”, IBM Technical Disclosure Bulletin, vol. 32, No. 9A, Feb. 1990, pp. 94-95.
Danen et al., “Index Decode Validity Check Circuit”, IBM Technical Disclosure Bulletin, vol. 26, No. 3B, Aug. 1983, pp. 1675-1676.
Blaum Mario
Hetzler Steven R.
Kabelac William John
Berthold Thomas R.
International Business Machines - Corporation
Sniezek Andrew L.
LandOfFree
Disk drive with sector numbers encoded by sequences of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Disk drive with sector numbers encoded by sequences of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Disk drive with sector numbers encoded by sequences of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2510996