Error correction capability varied with track location on a magnetic or

Abstract

A method for implementing error-correcting codes for disks, wherein the statistics of error vary according to the radius of the location being accessed. A Reed-Solomon code is selected having data bytes and redundant bytes and an error-correcting capability sufficient to protect against an anticipated worst case or errors. The number of redundant bytes in that code, and thereby the number of correctable errors, is progressively reduced in respective concentric areas of the disk according to the statistics of error for such areas, for thereby progressively reducing the number of correctable errors as the need for error correction capability decreases. For multiband recording, the areas are concentric bands in each of which data is recorded at a clock frequency substantially proportional to its inner diameter; and in such case, the number of redundant bytes is reduced progressively in each successive band toward the innermost band. For conventional recording, the areas are concentric tracks recorded at substantially the same frequency; and in such case, the number of redundant bytes is reduced toward the outermost concentric area. This method may also be used to increase correction capability periodically when capability decreases, due for example to corrosion of a write-once optical disk.