Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data verification
Patent
1997-10-21
2000-03-28
Kim, W. Chris
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data verification
714769, G11B 509
Patent
active
060439467
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to a method and apparatus for improving read error recovery operations in a disc drive through the of read channel quality indicators.
BACKGROUND ART
Disc drives are commonly used in workstations, personal computers, laptops and other computer systems to store large amounts of data in a form that can be made readily available to a user. Such drives store and retrieve data using one or more magnetizable discs that are rotated at a constant high speed by a spindle motor. Each of the discs has a magnetizable surface coating that can be selectively magnetized by a corresponding read/write head so that the data is stored in the form of magnetic flux transitions along defined data tracks on the surface of the disc.
The heads are typically suspended over the discs and positionably controlled with respect to the tracks on the discs through the use of a rotary actuator assembly and a servo loop. The servo loop obtains position information from servo fields on the discs and, in response thereto, corrects the radial position of the heads through application of current to an actuator coil. The coil is part of a voice coil motor, which as will be recognized comprises one or more permanent magnets which establish a magnetic field through which the coil moves; the magnetic interaction between the magnetic field of the permanent magnets and magnetic fields established in the coil as a result of the coil current causes the rotary actuator to position the heads as desired over the surfaces of the discs.
Heads can be of a variety of constructions, including thin film and magneto-resistive (MR). Both of these well known types of heads generally write data to a corresponding disc through the application of a write current of a selected duration, magnitude and direction to a write element of the head, the write element including a magnetic coil with a relatively small air gap. The gap, disposed in close proximity to the surface of the rotating disc, selectively magnetizes the disc as a result of the magnetic fields established across the gap in response to the write current. The approaches taken by thin film heads and MR heads to read data from the disc, however, are rather different. A thin film head senses magnetic transitions from a gap of a read element (which may or may not be the same as the write element) and outputs a read signal indicative of the selective changes in magnetization of the selected data track being read; an MR head, on the other hand, typically includes a magneto-resistive element characterized in that the presence of a magnetic field of a particular orientation changes the nominal dc resistance of the MR-element. Thus, variations in the magnitude of a predetermined read current passed through the MR-element during a read operation are taken as resulting from the interaction between the MR-element and flux transitions on the disc and such variations are translated into a read signal.
A read channel is typically provided to convert the read signal obtained from a selected head to the user data which was originally stored on the selected track. Such read channels are well known and can utilize a variety of signal processing techniques, including peak detection and partial response, maximum-likelihood (PRML) processing. To ensure reliable storage and retrieval operations by the disc drive, the user data is typically encoded with run length limited (RLL) and error correction codes (ECC) before being serially written to disc. As will be recognized, RLL encoding is provided to ensure the generation of appropriate read timing windows for the read channel and ECC is used to detect and correct up to a selected number of errors in the retrieved sequence. Thus, typical read channel operation includes RLL decoding and ECC operations upon the retrieved read signal in order to ultimately reconstruct the user data.
Error correction codes are a powerful tool for extra
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Genheimer Stephen R.
Shaver Jimmie R.
Kim W. Chris
Neal Regina Y.
Seagate Technology Inc.
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