Systematic memory error detection and correction apparatus and method

Abstract

A systematic data memory error detection and correction apparatus periodically reads data from each addressable memory location, determines the presence or absence of an error in the addressed data memory location and, if an error is detected, corrects the error and writes the corrected data back into the addressed memory location. The apparatus may include circuitry for logging those areas of the data memory where errors have been detected, such logging showing either the address location where an error is detected or alternatively indicating the repetitiveness of an error at any particular addressed memory location. Such data logging facilitates determination of hardware or 'hard' type errors as distinguished from non-hardware or 'soft' type errors. The latter type errors are typically found in dynamic random access memories (dynamic RAM's) which occasionally and randomly have errors due to bombardment of cosmic energy and alpha particles, the latter typically due to minute radioactive elements in silicon materials used in the fabrication of such memories. When the present apparatus is used in conjunction with dynamic RAM's, the error detection and correction is typically performed during 'refresh' times which are necessary for maintaining proper stored charge in such devices. By so doing, the access performance of the memory is not degraded by the error detection and correction apparatus.