Exploiting successive identical words and differences with dynamic bases for effective compression in Non-Volatile Memories

Abstract

Emerging Non-volatile memories are considered as potential candidates for replacing traditional DRAM in main memory. However, downsides like long write latency, high write energy, and low write endurance make their direct adoption in the memory hierarchy challenging. Approaches that reduce the number of bits written are beneficial to overcome such drawbacks. In this direction, we propose a compression technique that reduces overall bits written to the NVM, thus improving its lifetime. The proposed method, SIBR, compresses the incoming blocks to PCM by either eliminating the words to be written or by reducing the number of bits written for each word. For the former, words that have either zero content or are identical to consecutive words are not written. The latter is done by computing the difference of each word with a base word and storing only the difference (or delta) instead of the full word. The novelty of our contribution is to update the base word at run-time, thus achieving better compression. It is shown that computing the delta with a dynamically decided base compared to a fixed base gives smaller delta values. The dynamic base is another word in the same block. SIBR outperforms two state-of-the-art compression techniques by achieving a fairly low compression ratio and high coverage. Experimental results show a substantial reduction in bit-flips and improvement in lifetime.