Insights using NAND flash in portable designs

Lane Mason and Robert Pierce, Denali Software
(11/08/2007 2:15 PM EST) -- EE Times

As the raging success of Apple's iPod still rings in our ears, NAND flash memory is seen as the rising star of solid-state memory for portable and consumer applications.

This acceptance and use has largely been caused by NAND flash memory's rapid decline in price over the past three to four years (approximately 50 percent per year), which places it in a very competitive position (along with its other positive attributes) in relation to more established media such as tape, compact discs and magnetic hard disk drives. In addition to its low cost per gigabyte, it is touted as being more shock resistant than CDs or HDDs, more compact (smaller form factor) for the small configurations needed in most of today's consumer applications and more systemically consistent with the remainder of the solid-state electronic system, MPU or APU and analog circuitry. Flash memory requires no mechanical parts and no read sensor to track location on the disk. It does, however, require much lower power (operating and standby) in this era of heightened power consciousness.

Even with all these good product attributes and its low cost, NAND flash memory still has some work to do to convince users that it is better than its storage alternatives.

Most flash users are concerned with single-level cell (SLC) and multi-level cell (MLC) endurance because of the wearing-out of mechanisms for reading and writing the stored charge in the oxide layer. If infinite reads and writes are necessary, NAND flash memory will not work. If 100K read/write cycles are good enough, SLC is the way to go. However, if 3K to 10K read/write cycles are consistent with the lifetime of your NAND-containing product, then MLC might be a better choice.

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