ZOCHEN: Compression using Zero chain elimination and encoding to improve endurance of Non-volatile Memories

Nishant Bharti1, Arijit Nath2, Swati Upadhyay1, Hemangee Kapoor3
1IIT Guwahati, 2IIT Guwahati, India, 3Indian Institute of Technology Guwahati


Emerging Non-Volatile memories (NVM) offer immense possibilities to be considered as an alternative to DRAM in the main memory. However, adoption of NVMs in the memory hierarchy faces challenges due to their costly writes and poor write endurance. In this connection, developing policies to improve the endurance of NVMs has paramount importance. This paper presents a low overhead scheme based on compression and encoding to improve the lifetime of PCM-based main memory. We propose a compression technique by removing chains of zero-valued data bits that are prevalent in the cache blocks coming to PCM. On top of it, we encode the compressed blocks at finer encoding granularity, utilizing only a few tag bits. The overall procedure, called ZOCHEN improves PCM lifetime by reducing bit-flips in the PCM cells. We get a substantial reduction in bit-flips and improvement in lifetime compared to baseline and state-of-the-art policies.