NAND & NOR Flash Memory

NOR Flash is designed for use in linear program storage for applications such as boot loaders and BIOS, with its key benefit being the ability to satisfy requirements that need to read code wherein each word of data is needed to carry out instructions.

NAND Flash is optimized for file structures where each word does not need to be read, but instead provides that sectors of data can be moved to and from media supporting a hard drive like repository structure for data storage to support file systems and allocation tables (FAT)

NOR Flash is generally much smaller than NAND Flash or a MB/Device basis, and much more expensive on a $/MB basis. However, unlike NOR Flash, inherent to NAND Flash technology is the occurrence of bad blocks. These bad blocks might not readily appear, and can occur after the memory has been successfully in use but prior to reaching the expected number of write/erase cycles. The use of NAND Flash therefore demands that some sort of mechanism, such as TrueFFS, can be implemented to map these bad blocks.

Both NOR and NAND Flash have a limited number of write/erase cycles. Wear-leveling algorithms such as found in TrueFFS can be used so that Flash components in an array are accessed at the same level of write/erase cycles to avoid repeatedly writing erase the same location. By virtual mapping of logical sectors to physical blocks, the entire memory array is utilized/degraded evenly.

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