Online memory fault detecting method and device

The invention provides an online memory fault detecting method and device. The method comprises writing data in a CPU (central processing unit) into a working memory and a mapping memory simultaneously; performing real-time bit-by-bit comparison on the data of the CPU, which are written into the working memory and the mapping memory through a comparing unit; when the memory comparison results are identical, determining the memories work normally; if the memory comparison results are not identical, determining that the memories fail and performing corresponding treatment; writing different data into virtual space outside the memory space and the mapping memory simultaneously through the CPU and performing real-time bit-by-bit comparison through the comparing unit to achieve self-inspection of the comparing unit; when the self-inspection results are identical, determining that the comparing unit fails; when the self-inspection results are not identical, determining that the comparing unit works normally. The on