Error Control Schemes for Modern Flash Memories: An Overview

Dramatic improvement in Flash technology over the course of the last decade has led to cheaper and denser Flash devices. The great expansion in information capacity in Flash devices mandates the use of improved error-correcting codes, in terms of both efficiency and reliability. This trend is likely to continue as we transition from single-level cell (SLC) Flash memories to increasingly dense multi-level cell (MLC) devices. Moreover, as Flash drives make inroads into the enterprise storage domain, these concerns will become increasingly significant. Error-correcting codes, long used for many types of computer memories and storage media, offer a crucial solution to Flash deficiencies. In this paper, we discuss the causes of Flash problems and identify how error-correcting codes are capable of resolving these issues in order to improve reliability and extend device lifetimes. We describe several approaches to error-correction coding for Flash. These approaches include traditional Hamming codes (also used in memories), Reed-Solomon codes (used in optical media, such as CD and DVD technology), BCH codes, and LDPC codes. We also describe some promising future directions.