Method and apparatus for writing and protecting against random and

Abstract

A method and apparatus for encoding and detecting data which can be represented in a physical array of modules recorded on a medium. Information is encoded in 'image-blocks'. An image-block comprises a plurality of 'sub-blocks'. Sub-blocks comprise a plurality of 'modules'. A module is the smallest unit of information within the image-block. Discrete contiguous portions of each sub-block of an image-block taken together are encoded into an outer codeword. A plurality of these outer codewords are generated and recorded across each sub-block. A portion of the information that is to be recorded within each sub-block is encoded in a plurality of inner error detection and correction codewords, each preferably stored entirely within one corresponding sub-block. Accordingly, small scattered random errors can be corrected locally by using information entirely contained within the sub-block. If a large area within a sub-block is corrupted, the information contained in each other sub-block may be used to reconstruct the data that was recorded in the corrupted sub-block. The inner codewords are 'interleaved' to provide a maximum distance between parts of the same codeword.