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IBM's 6250 bpi 3420 series tape units require a powerful error-correcting code for the standard 9-track format. The optimal rectangular code (ORC), presented here, is designed to correct any single-track error or, given erasure pointers, any double-track error in the tape. The code achieves this by conforming to a rectangular codeword of which two orthogonal sides are check bits. The code is specially tailored from a general class of b-adjacent codes. The ORC can be implemented without a buffer for encoding and offers a simple error-correction mechanism. The code can be generalized to multiple-channel applications.
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