Code Shadowing: Closing The Performance Gap For NAND-Flash Only Systems

With demands for embedded nonvolatile memory increasing, NAND Flash is becoming a more attractive alternative as the only nonvolatile storage media in a system. Using NAND Flash in combination with Mobile DRAM increases a system's available nonvolatile memory and can reduce system cost by removing the need for NOR Flash devices.

NAND Flash successfully meets the escalating market demand for high-density, nonvolatile discrete memory solutions in embedded and mobile systems. NAND Flash is already incorporated into many newer embedded designs. There are, however, many embedded systems that have not adopted NAND Flash—systems that rely on eXecute-In-Place (XIP) functionality. Consequently, many embedded designs implement NOR Flash and NAND Flash side by side.

NOR Flash Considerations

At first glance, NOR Flash appears to be an obvious choice. It provides direct XIP access and offers designers a familiar, mature product for which they have already developed code and hardware interfaces to support implementation. The drawback to NOR Flash, however, is its limited density—hence, the need for two nonvolatile memory devices: NOR for code execution and NAND for high-capacity data storage.