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NAND Flash

Learn more about NAND flash by attending the Flash Memory Summit.

An Introduction to NAND Flash

For many consumer audio and video products, NAND flash memory is a better storage choice than a hard drive, especially in low-capacity applications (4 Gbytes or less). As the quest continues for lower power, lighter, more robust products, NAND flash is proving to be very attractive.

The NAND flash array is grouped into a series of 128-kbyte blocks, which are the smallest erasable entity in a NAND flash device. Erasing a block sets all bits to "1" (all bytes to FFh). Programming is necessary to change erased bits from a 1 to a 0. The smallest entity that can be programmed is a byte. Although NAND flash can't perform read and write simultaneously, it can accomplish this at a system level using a method called shadowing, which has been used on PCs for years by loading the BIOS from the slower ROM into the higher-speed RAM.

NAND flash efficiencies are due to the lack of metal contacts in the NAND flash string.

NAND flash is similar to a hard-disk drive. It's sector-based (page-based) and suited for storing sequential data such as pictures, audio, or PC data. Although random access can be accomplished at the system level by shadowing the data to RAM, doing so requires additional RAM storage. Also, like a hard disk, NAND flash devices have bad blocks, and require error-correcting code (ECC) to maintain data integrity.

Due to the decrease in die area resulting from the small cell size, NAND flash provides the larger capacities required for today's low-cost consumer market. NAND flash is used in almost all removable memory cards. NAND flash's multiplexed interface provides a similar pin-out for all recent devices and densities. This pin-out lets designers use small densities and migrate to larger densities without any hardware changes to the pcb.

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