Reliability of semiconductor RAMs with soft-error scrubbing techniques

Error control codes are widely used to improve the reliability of random-access memory (RAM) systems. The paper evaluates the reliability of coded memory systems suffering both hard (permanent) errors and soft (transient) errors. The technique of soft error scrubbing, that is periodically removing all soft errors to improve the system reliability, is studied for RAM systems with chip-level coding only (one-level fault tolerance) and both board-level and chip-level codings (two-level fault tolerance). Previous work, which covers hard errors only, is extended to include the technique of soft-error scrubbing. In addition, the assumption that the error rates among the different memory components are the same is removed. The result offers a simple and low-computational way of estimating the reliability of semiconductor RAMs protected by the error control codes