Flash in the Pan

Nathan Edwards

Flash memory could become the dominant form of mass storage, replacing magnetic and optical media for many purposes. Although flash retains data without requiring power, the memory cells don’t retain their charges forever. Eventually, the charges dissipate and the bits fade away. Will our data be a flash in the pan?

Consider the trends. USB thumb drives are commonplace, and solid-state drives (SSDs) are appearing in subnotebook computers like the Asus Eee PC and Macintosh Air. SSDs are still too expensive to replace conventional drives in desktop PCs, but some hard drives use small amounts of flash to store startup data, which shortens boot times.

Flash already rules in consumer electronics. Lately, I’ve seen 2GB memory cards for $8. In my 10.2-megapixel DSLR, a 2GB card stores 264 pictures in highest-quality format. The cost per picture is half as much as using film—even if I don’t reuse the card. And that calculation excludes the cost of developing the film. So why not use the card only once, instead of copying archives onto other media?

Unfortunately, vendors of thumb drives and memory cards are vague about data retention. Usually, they estimate 10 to 20 years. Actually, the data can last much longer.

Research shows that some cells in every flash chip lose their charge relatively quickly. The remaining cells stay charged for decades. Eventually, the number of cells losing charges rises again, until all data is lost.

Heat speeds up the process. Manufacturers can produce long-living flash chips by baking them at high temperatures (up to 482 F) for long periods (up to three weeks) to kill off the “weak” cells, leaving only the “strong” ones. Afterward, accelerated aging tests indicate that data retention at room temperature can exceed 1,000 years. However, it’s unlikely that mass-market flash chips will get this expensive treatment.

To be safe, then, keep your flash memory cool and rewrite the data every 10 years or so. Although magnetic and optical media typically last much longer, they can fail prematurely, too. When preserving vital data, nothing beats making regular backups on multiple types of media. Sorry!

Tom Halfhill was formerly a senior editor for Byte magazine and is now an analyst for Microprocessor Report .

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