Proceedings of the IEEE/ACM Int'l Symposium on Microarchitecture (MICRO), pp. 347~357, New York, NY, December 2009.
The PRAM (phase-change random access memory) technology is fast maturing to production levels. Main advantages of this technology are non-volatility, byte addressability, in-place programmability, low-power operation, and higher write endurance than that of the current flash memory family. However, the PRAM's relatively low write bandwidth and less-than-desirable write endurance remain room for further improvement. This paper proposes and evaluates Flip-N-Write, a simple microarchitectural technique to replace a PRAM write operation with a more efficient read-modify-write operation. On a write, after quick bit-by-bit inspection of the original data word and the new data word, Flip-N-Write writes either the new data word itself or the "flipped" value of it. Flip-N-Write introduces a single bit associated with each PRAM word to indicate whether the PRAM word has been flipped or not. We analytically and experimentally show that the proposed technique reduces the PRAM write time by half, more than doubles the write endurance, and achieves commensurate savings in write energy. Due to its simplicity, Flip-N-Write is straightforward to implement within a PRAM device.