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Advances in semiconductor memory technology towards higher-density and higher-performance memory chips have created new reliability challenges for the memory system designer. An example would be the multiple-bit-per-chip organization with the chip outputs used in the same word. This design structure would be prone to uncorrectable errors with conventionally implemented single-error-correcting double-error-detecting codes. With these newer chips, memory system designers will have to give special attention not only to the types of failures but to ways of minimizing the system impact of reliability defects. In this paper, a number of design approaches are presented for minimizing the effects of chip failures through the use of organizational techniques and through enhancements to conventional error checking and correction facilities. The fault-tolerant design techniques described are compatible with most existing memory designs. An evaluative comparison of these techniques is included, and their application and utility are discussed.
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