Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1993-01-13
1994-09-13
Dzierzynski, Paul M.
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
369 47, 369 59, 360 32, 360 39, G11B 726, G11B 509
Patent
active
053475097
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates generally to media carrying symbols representing digital information, the recovery from media of symbols representing digital information and the establishment of the digital information represented by such symbols. While the present invention has many applications, it is more particularly described in connection with preferred embodiments in which the symbols are recovered from and carried by tape- and disk-based storage media in which the symbols are arranged in spiral, concentric, parallel or linear tracks.
2. Background Art
The expanding use of digital computers and digital processing has heightened interest in finding methods and apparatuses for more efficient retrieval of digital information from storage media. More efficient information storage retrieval includes advances in the art such as increased information storage capacities, reduced information access times, and reduced apparatus and medium costs.
Commonly used storage techniques utilize magnetic and laser-optical technologies to store and retrieve digital information on tape- and disk-based storage media. The digital information is usually arranged on the medium in linear sequences or "tracks" of binary-valued symbols. Magnetic tape, for example, may store digital information as magnetic flux changes within one or more tracks arranged either along the length of the tape or diagonally across the width of the tape. A magnetic disk commonly stores digital information as magnetic flux changes within tracks arranged in concentric circles about the center of the disk. A laser-optical disk commonly stores digital information as reflective spots, either raised or flush with the surrounding reflective area of the disk, arranged within a track which spirals in toward the center of the disk.
The information storage capacity of a storage medium is established by the size of the medium and the density of the symbols carried by the medium. The density is established by the spacing between adjacent symbols within a track and by the spacing between adjacent tracks. For optical storage media having only one spiral-shaped track, the concept of adjacent tracks is understood to mean adjacent turns of the spiral. The "width" of a track is distinct from but related to the spacing between adjacent tracks; the width represents the dimension across a track transverse to its length. In most applications, the track width is smaller than the spacing between adjacent tracks thereby providing a "guard band" between adjacent tracks which is not used to store information.
Increases in information storage capacities have generally been achieved by decreasing the spacing between symbols arranged within a track and decreasing the spacing between adjacent tracks. Thus, high-capacity storage media tend to comprise a very large number of very narrow tracks spaced closely together.
Such increases in information storage capacity often increase the cost of the apparatus used to store and retrieve information because high-capacity storage media of this type imposes very demanding requirements upon the accuracy and speed of electro-mechanical apparatuses used to store and retrieve information. When an apparatus is called upon to store or retrieve information on a medium, an electro-mechanical actuator must move a magnetic "head" or optical "pickup" sensor accurately enough to position the sensor within the width of a particular track. This becomes more difficult as the track width becomes narrower.
In addition, such increases in information storage capacity frequently result in longer access times. The time required to accurately position a sensor, called the "seek time," is adversely affected by a number of factors including the distance or number of tracks over which the head must move, the accuracy with which the sensor must be positioned, and the mass of the sensor. It is difficult to achieve low seek times for high-capacity magnetic media because of the large number of closely spaced tracks, but it is especially diffi
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Goldberg Paul R.
Mandell Douglas E.
Richards Martin J.
Chu Kim-Kwok
Dolby Laboratories Licensing Corporation
Dzierzynski Paul M.
Gallagher Thomas A.
Lathrop David N.
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