What is NAND flash?
Answer:
Flash memory is a form of non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology i.e. primarily used in memory cards.
NAND memories
NAND flash memories cannot provide execute-in-place due to their different construction principles. These memories are access much like block devices such as complicated disks or memory cards. The blocks are typically 512 or 2048 bytes in size. Associated near each block are a few bytes (typically 12–16 bytes) that should be used for storage of an error detection and correction block checksum.
NAND devices typically hold software-based bad block administration. This means that when a logical block is access it is mapped to a physical block, and the device have a number of blocks set aside for compensating fruitless blocks and for storing primary and secondary map tables.
The error-correcting and detecting checksum will typically correct an error where on earth one bit in the block is incorrect. When this happen, the block is marked fruitless in a logical block allocation table, and its (still undamaged) contents are copied to a fresh block and the logical block allocation table is altered accordingly. If more than one bit surrounded by the memory is corrupted, the contents are partly lost, i.e. it is no longer possible to re-establish the original contents. Some devices may even come near a pre-programmed bad block table from the businesswoman, since it is sometimes impossible to manufacture error-free NAND memories.
The first error-free physical block (block 0) is other guaranteed to be readable and free from errors. Hence, all decisive pointers for partitioning and bad block regulation for the device must be located inside this block (typically a pointer to the bad block table etc). If the device is used for booting a system, this block may contain the master boot record.
When executing software from NAND memories, virtual memory strategies are used: memory contents must first be page or copied into memory-mapped RAM and executed there. A memory supervision unit (MMU) surrounded by the system is helpful, but this can also be expert with overlays.
For this point, 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 beside a file system for use as a messy access storage area.
NAND is best suited to flash devices requiring dignified capacity notes storage.This type of flash architecture offers storage space up to 512-MB and have faster erase, write, and read capabilities over NOR architecture.
NAND flash architecture be introduced by Toshiba in 1989.
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