Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2000-05-24
2004-06-08
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S031000, C360S053000
Reexamination Certificate
active
06747825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for passing over, or more specifically slipping, defective sectors on disc surfaces within a disc drive.
BACKGROUND OF THE INVENTION
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (“ABS”) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
In a disc drive having more than one surface on which to record data, the tracks at substantially the same radial distance from the center of the disc or discs are said to be in a cylinder. The cylinder is one unit of storage which includes several tracks. Each these cylinders and each track on a disc surface in a disc drive is further divided into a number of short arcs called sectors. The sector typically holds 512 bytes of information representing data. The number of sectors on a track used to be fixed wherever the track was located on the disc surface. Now, the number of sectors held on a track or within a cylinder varies depending on the zone which the track or cylinder is in. Typically, more sectors will be stored on the tracks and in the cylinders at the outer diameter which are in the zone toward the outer diameter of the disc.
Each sector in a disc drive is individually addressable. In order to locate the data, each sector is given a unique address, known as the physical cylinder, physical head and physical sector number. Some term this as the physical cylinder, head and sector (PCHS). Given these three parameters, the location of any sector can be determined.
When a disc is manufactured, there is a possibility that there may be defects on the disc. The defects typically can result in sectors or tracks that have doubtful, dangerous, or damaged magnetic media, which would otherwise put the customer's data at risk. These defects are to be avoided so that information representative of data is not written to a location where the data could be lost. Typically, each disc surface is checked for defects at the time of manufacture. A sector is considered defective if a number of retries must be used to recover the data on the sector. A sector is also considered defective if data written to the sector is not recoverable. The sectors occupying these locations are named as defects. These defects cannot be used for data storage and hence cannot be presented to the host computer for access.
Of course, avoiding the defective sectors can be done in any of a number of ways but each way requires keeping the defect in memory. In most disc drives, the defect management system has adopted a method of sector address translation, which simplifies the tasks of a host computer by offloading the tasks to the controller of a disc drive. The drive presents to a host computer, a collection of good sectors known as the logical block address (LBAs). Based on a known list of defects, the firmware of the disc drive translates the LBA to a physical cylinder, head and sector location (PCHS). While accessing the physical sector address in the sequential order, the defective sectors are skipped over. Therefore, every LBA is mapped to a unique physical cylinder, head and sector (PCHS) in the disc drive. Data files and program files are typically much larger than the number of bytes allocated to a sector. As a result, data and program files are divided and stored on disc drives as a number of LBAs. The actual methods of doing this are unique to every operating system. Before the disc drive can be used for this purpose, the operating system formats the disc drive by creating a lookup table of its own to map the data and program files to every LBA in the disc drive.
Every operating system employs a unique look up table method to locate data and program files in a disc drive. While the location of data and program files in the disc drives can change the location of these lookup tables are fixed during the formatting of the disc drive and will not change until the disc drive is reformatted again.
A typical data or file access requires the operating system to read the LBA containing the directory of filenames. The directory of filenames is read to determine if the file is available on the particular disc drive. If the file is found in the directory, the directory is read and contains information regarding the beginning 25A of the file. Another table, referred to as the file allocation table (FAT) includes the information. If the file that describes the location of the entire file. Finally, the disc drive proceeds to read the requested file into the memory. This can be summarized below:
1. End user request to read a data file.
2. Operating system search for the file in its director.
3. When file is found, operating system reads a file-allocation table describing all the LBA and order of the LBA which make up the data file.
4. Operating system finally proceeds to read the data file for the user.
In order to complete each read command to read data, both the directory and the file allocation tables are read. Of course, the majority of the time the da
Chan Wesley Wing Hung
Chng YongPeng
Ng Wei Loon
Quak Beng Wee
Wong Patrick Tai Heng
Davidson Dan I.
Hudspeth David
JPMorgan Chase Bank, As Collateral Agent
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