Excavating
Patent
1996-10-29
1999-05-04
Baker, Stephen M.
Excavating
371 374, H03M 1300
Patent
active
059011572
ABSTRACT:
Frequently only a portion of the data within an error correction data block is required to be changed or overwritten. For example in optical data storage on DVD type discs, an error correction block contains 32K bytes of user data, however, a computer system typically operates on 2K byte sectors and therefore frequently does not involve the full 32K byte block. In these circumstances the old data block must be read, error corrected, the new data combined with the old and new error correction redundancy bytes calculated. This invention is a method and apparatus of improving access time when only a portion of the data in an error correction data block is modified. The contributions to the redundancy bytes in the codewords, due to the old data to be modified and the new data to be written, are calculated. Required modifications to the old redundancy bytes can be calculated by parity checking (multiple exclusive or-ing), or by matrix operations and implemented by exclusive or-ing the modifications with the old redundancy bytes. This modification process need only involve the portion of the data that is to be modified and can make the new redundancy bytes available rapidly, thereby improving access time.
REFERENCES:
patent: 5283791 (1994-02-01), Halford
patent: 5285451 (1994-02-01), Henson
Baker Stephen M.
Hewlett--Packard Company
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