Use of Error Correcting Codes on Memory Words for Improved Reliability

Application of error correcting coding is often employed to improve system operation and reliability. By means of suitable reliability models and simple analysis, the effect of error correcting coding of memory words on the overall reliability of the system is discussed. Introduction of error correcting facilities will generally have three significant effects on the system: 1) increased hardware, which is also subject to failures and hence tends to lower reliability; 2) the system´s ability to function in the presence of a certain class of failures; and 3) quicker detection of errors, which also means an improved repair rate. To illustrate the extent to which the above three factors govern the reliability improvement due to coding, three types of systems are considered. These systems use the same basic processor and memory units but differ in their structure and complexity. Other factors besides the three above which control the reliability improvement due to coding are the system structure and the relative sizes of processor and memory hardware.