Duplex and Triplex Memory: Which Is More Reliable?

A large number of choices exist when designing a reliable memory system. The choices range from simple replication to complex error control codes (ECC). Simple replication (without ECC) has a better performance as compared to systems using ECC, as ECC necessitate decoding, deteriorating the performance. Clearly, simple replication improves performance at the cost of increased redundancy. An intermediate solution is to use combination of replication and simple ECC. Similar approach has been used in some commercial systems [1]. This report compares reliability of memory systems formed using simple triplication (without ECC) with memory systems formed by duplicating memory modules that use ECC. Reliability of a system using duplication of memory modules, with codes capable of only error detection or codes only capable of single error correction, is shown to be worse than simple triplication. It is also shown that systems using duplication of memory modules, with codes capable of single error correction and double error detection can achieve better reliability than simple triplication.