Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal gain processing
Reexamination Certificate
1998-08-12
2001-02-06
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal gain processing
C369S047360, C369S124010
Reexamination Certificate
active
06185174
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to pulse data recovery in optical media disk drive data storage systems. More specifically, the present invention relates to data recovery systems that rely on recovering stored data from pulse waveforms having varied peak amplitude and/or varying peak instances relative to a known time base.
BACKGROUND ART
Disk data storage systems generally use either magneto-inductive, magneto-resistive, magneto-optical or purely optical data recording/reading techniques with the appropriate media. Data is stored on the disk media in an organized manner designed to cooperate with the electrical and mechanical control components of the disk drive system.
In optical and magneto-optical disks the areas on the disks are typically organized or formatted with different areas dedicated to different functions. A central portion of the disk may contain a start up zone which is used to calibrate the system when it is initialized. User data is arranged in a number of spaced apart data sectors extending radially outward from the start up zone to the disk outer diameter. User data sectors are typically separated by servo sectors. The servo sectors contain information used by the system to identify particular data storage locations by some reference coordinate system, typically radial and circumferential measures relative to some reference origin location.
Radial bars of data bits on the disk can be used to define circumferential position, (i.e., index sector number, e.g., sector 1, 2, . . . , recoverable by a read/write head and processed by a disk drive control system). Magnetic disks are commonly written with similar servo sectors defined in magnetic form.
Servo patterns are generally of constant angular spacing for good reason; it greatly simplifies reading the circumferential position at any radius.
User data is typically stored in a plurality of semi circular arc segments of contiguous data bit locations concentrically disposed about the disk center. The user data arc segments are disposed between semi circular arc segments of data bit locations that include servo sector data bits and may include other system information. The servo sector data bits may include a servo timing mark, or STM. The STM can be encoded to provide coarse disk position information to the system; for example to define which of the radially spaced semicircles is under the read/write head.
Magnetic recording and reading of data patterns typically results in a recovered data signal having two immediately adjacent pulses of opposite sign indicating the transition between two adjacent and oppositely magnetized magnetic domains. The transition from one magnetization to the other can be used to indicate a change in stored user data from one binary logic value to its opposite.
Magneto-resistive, optical and magneto-optical data recording and reading generally results in a unipolar pulse indicating the presence of a binary logic value and the absence of the unipolar pulse indicating the opposite logic value. The unipolar pulse results from an increase (or decrease) in amplitude of a returned signal picked up by the read/write head from the disk. The returned signal is generally a response to a constant intensity source signal directed at the recording area (the data bits) of the disk by the read/write head as the disk surface passes thereunder.
In the unipolar data pulse case, typical of optical and magneto-optical drives, timing of the pulses (and their absence) becomes very important in order to properly recognize the logic value associated with pulse presence/absence. This is accomplished by a writing means for writing data into data bit locations of the disk system and a reading means for reading data pulses from data bit locations having stored data. This is nearly always associated with a fixed system clock associated with the reading device, which may be different from a fixed clock provided by the data writing device.
In magneto-optical drives, advantage can be had by making the servo sector data writing/reading means orthogonal to the user data reading/writing means. For example the servo sector data bits can be read by a photosensitive device as attenuated reflection of an incident laser beam from pits written by laser pulses from a master writer device on an otherwise uniformly reflecting disk surface. Conversely the user data can be read by a polarization sensitive device from polarized reflected light from user data locations on the uniformly reflecting surface written by magneto-optic polarization shifting effects (the Kerr effect).
In the unipolar data pulse environment provided by a magneto-optical drive, radial bars (i.e., pits formed in contiguous overlapping radial alignment) in the servo sector may be used to aid the disk system in identifying circumferential position of data sectors. An index or reference origin sector can be defined with the following sectors, sector number 0, sector one, sector two, etc.
One example of an architecture for a disk format is the NOID system from IBM (TM). One purpose of the NOID system is to encode a coordinate system (radial and angular position) on the disk without the use of gross physical elements. Radial and angular position coordinates on the disk are described by the data architecture or format of the servo sectors.
In magnetic disk technology, this information is written magnetically on the disk. In optical or magneto-optical disk technology the servo sector data information may be molded or embossed permanently into the recording surface. Typically a master disk is written with a formatted system data pattern (servo sector data and the like) using a precise laser beam master writing system to expose a photo resist coated master disk. A photolithographic development and etching process then leaves micro pits or indentations that form the embedded servo information. Currently master disks having servo data bits with about two nm position accuracy can be made commercially by firms having suitable master disk laser writing equipment. Daughter disks containing the embedded servo and coordinate system data can then be printed from the master disk for use in end-user systems.
Servo sector data patterns are typically written with constant angular spacing between adjacent bit locations. This simplifies servo data recognition although this causes lower servo data density toward the outer perimeter of the disks. Thus, careful attention to the architecture of the servo data is important to insure efficient use of costly disk area. If the servo sector data bit locations were not of constant angular spacing, the disk system would have to recognize variable frequency encoded data in the servo sector. Doing this by using pulse data decoding channels incorporating variable frequency oscillators (VFO's) is possible. VFO's however, typically take a long time to synchronize, i.e., taking up many bits, so a servo sector data field for use with a variable frequency oscillator data retrieval channel would be too long for efficient formatting.
The read/write head of the disk drive system is positioned on the disk surface by a read/write head servo system. The read/write head is typically positioned approximately radially along the disk surface by an actuator arm having a rotary base assembly mounted adjacently to the disk outer perimeter. The designer of the servo system driving the actuator arm, having knowledge of the geometry of the system can design the system to use the present track number information obtained from the servo sector data, to move the head rapidly to the radial position where the next target track is located.
By reading the STM and encoded system coordinate information of each sector as it passes under the read/write head, a disk drive control system (DDCS) may derive the ID number and relative arrival timing of the servo sectors. The DDCS is typically provided with means to synchronize read and write commands to the read/write head to access the recorded user data bits at a desired data track segm
Dempster Shawn B.
Edun Muhammad
Heller Edward
Seagate Technology LLC
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