Dynamic information storage or retrieval – Systems having plural physically distinct independent tracks... – Having layered storage medium
Reexamination Certificate
2002-09-20
2004-11-30
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Systems having plural physically distinct independent tracks...
Having layered storage medium
C369S047190, C369S124020, C369S124040, C369S059220
Reexamination Certificate
active
06826140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention is a system for storage and retrieval of digital data. More particularly, the present invention involves processing digital recorded material with joint signal detection techniques.
2. Background Art
Digital data storage devices, such as computer drives and portable tapes, compact discs and floppy diskettes, are recording components in many electronic devices, and typically provide mechanisms for storing and retrieving large amounts of data quickly and reliably. Digital recorders, as used herein, refer to the many embodiments employed for storing digital information in a variety of digital systems and a multitude of applications. The most common form of digital recorder is a rotating radial magnetic disk. Other digital recorders include but are not limited to optical disks and magnetic tape systems, including linear devices.
The prior art disk drive system is well known in the art. A data storage disk, such as floppy disks, hard disks, and cubical disks as well as linear and multi-level disks all function in a similar fashion. The common radial disk contains a number of concentric data cylinders that contains several data sectors. The sectors are located on an upper side of the disk and additional sectors may be located on a lower side or in multiple layers within the disk. The disk is accessed by a head element mounted on an arm that is secured to the drive. The disk is accessed via photoemitters/photoreceptors for optical systems and with magnetic read/write elements as discussed herein for magnetic systems wherein various accompanying electronic circuits are familiar to those of skill in the art.
Using disk drives as an example, the disk is typically subdivided into one or more partitions by using a partition table that is located on the disk. A wide variety of partitions file systems as discussed in the prior art are not necessary for a proper understanding of the present invention. A given sector on the disk is usually identified by specifying a head, a cylinder, and a sector within the cylinder. A triplet specifying the head number, cylinder number, and sector number in this manner is known as a physical sector address. Alternatively, a given sector may be identified by a logical sector address, which is a single number rather than a triplet of numbers.
In more specific detail, for a data storage device, such as a magnetic disc drive, the recording medium is typically divided into a plurality of generally parallel data tracks. The data is stored and retrieved by a transducer or head element that is positioned over a desired data track by an actuator arm. The head element can be a combined read/write head or separated into a read head and a write head in close proximity.
The actuator arm typically moves the head across the data tracks under the control of a closed-loop servo system based on servo data stored on the disc surface within dedicated servo fields. The servo fields can be interleaved with data sectors on the disc surface or on a separate disc surface that is dedicated to storing servo information. As the head passes over the servo fields, it generates a readback servo signal that identifies the location of the head relative to the centerline of the desired track. Based on this location, the servo system rotates the actuator arm to adjust the head's position so that it moves to the desired position.
There are several prior art types of servo field patterns, such as a null-type servo pattern, a split-burst amplitude servo pattern, and a phase type servo pattern. A null type servo pattern includes at least two fields which are written at a known phase relation to one another. The first field is a phase or sync field which is used to lock the phase and frequency of the read channel to the phase and frequency of the read signal. The second field is a position error field that is used to identify the location of the head with respect to the track centerline.
In a typical prior art embodiment, as the head passes over the position error field, the amplitude and phase of the read signal indicates the magnitude and direction of the head offset with respect to the track centerline. The position error field has a null-type magnetization pattern such that when the head is directly straddling the track centerline, the amplitude of the readback signal is ideally zero. As the head moves away from the desired track centerline, the amplitude of the read signal increases. When the head is half-way between the desired track centerline and the centerline of the adjacent track, the read signal has a maximum amplitude. The magnetization pattern on one side of the centerline is written 180 degrees out of phase with the magnetization pattern on the other side of the centerline, and the phase of the read signal indicates the direction of the head position error.
To control the servo system, a single position error value is normally generated for each pass over the position error field. Typically, the magnitude of the position error value indicates the distance of the head from the track centerline, and the sign of the position error value indicates the direction of the head's displacement. The position error values are typically created by demodulating the read signal associated with the position error field. In a synchronous process, the exact phase of the read signal from the position error field is known from the phase field's read signal because the phase field is written on the storage medium at a known and fixed phase relation to the position error field. A phase-locked loop (PLL) is typically used to acquire the phase of the phase field, and this phase information is used for demodulating the position error field.
Processing of the read signal is generally demodulated by generating a demodulating signal, such as a square wave, having the same phase and frequency as a fundamental component of the read signal and then, with analog techniques, multiplying the read signal by the demodulating signal. The product is integrated over a time window that corresponds to the middle cycles of the position error field. The result is a position error value for the head with respect to a desired position on the storage medium within that servo pattern. This process essentially identifies the amplitude and phase of the read signal at a specific frequency point. The sign of the position error value indicates which direction the head is located with respect to the desired location.
The most common application for digital recorders is the computer disk drive. All sizes of computers including portable laptops, personal computers and mainframes include a digital recording system. Typically the recording device is a magnetic disk drive, but other devices such as optical disks and tape systems are also commonly used. Besides computers, other digital systems also use digital recorders, for example, digital video cameras write data to a digital recorder in the form magnetic tape, magnetic hard disks or optical disks.
Magnetic disc drives, because of their greater speeds, have become the medium of choice for storing frequently accessed data such as application programs and user data which is being created or frequently modified. Conventional magnetic disk drive storage systems have been commonly used and are well known in the art. These storage systems typically use a flying magnetic read/write head, either combined or separate read head and write head, to record and retrieve data from a layer of magnetic recording material on the surface of a rotating recording disk. The capacity of such a storage system is a function of the number of closely spaced concentric tracks on the recording disk that may be reliably accessed by the read/write head. Some parts of the recording disk surface area may be used for purposes other than data storage.
For example, means for assuring the proper selection of a particular track by the read/write head are required for reliable data storage and retrieval. The read/write head i
Brommer Karl D.
MacLeod Robert B.
Schmidt Michael P.
BAE Systems Information and Electronic Systems Integration INC
Maine & Asmus
Tran Thang V.
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