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NAND flash memories cannot provide execute-in-place due to their different construction principles. These memories are accessed much like block devices such as hard disks or memory cards. The blocks are typically 512 or 2048 bytes in size.

NAND devices have bad block management built into their circuitry. This means that when a logical block is accessed it is internally mapped to a physical block, and the device have a number of blocks set aside for compensating bad blocks and mapping tables.

When executing software from NAND memories, virtual memory strategies are used: memory contents must first be paged or copied into memory-mapped RAM and executed there. A memory management unit (MMU) in the system is helpful, but this can also be accomplished with careful programming.

For this reason, some systems will use a combination of NOR and NAND memories, where a smaller NOR memory is used as software ROM and a larger NAND memory is partitioned with a file system for use as a random access storage area.

This article is licensed under the GNU Free Documentation License. It uses material from the article: Flash memory - NAND Memory on the WIKIPEDIA

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