Data retention is a funny thing. Atmel will gladly tell you that the flash memory in an ATmega32A will retain its data for 100 years at room temperature. Microchip says its EEPROMs will retain data for over 200 years. And yet, humanity has barely had a good grasp on electricity for that long. Heck, the silicon chip itself was only invented in 1958. EEPROMs and flash storage are altogether younger themselves.
How can these manufacturers make such wild claims when there’s no way they could have tested their parts for such long periods of time? Are they just betting on the fact you won’t be around to chastise them in 2216 when your project suddenly fails due to bit rot.
Well, actually, there’s a very scientific answer. Enter the practice of accelerated wear testing.
Faster, Faster Now
EEPROM and NAND flash storage are both immensely important technologies. EEPROMs are used to store firmware for all kinds of devices, as well as things like cryptographic keys and other such largely-static data. Most EEPROMs have data retention ratings for many decades, if not centuries. Flash can be used in much the same way, but it’s also used as mass storage. It’s not quite as good at retention as EEPROM is. Some parts are rated for only a few years if left to sit, particularly at elevated temperatures. Other flash parts can hang on to data for much longer if designed to do so.
The question is, though, how we determine these numbers. Given the impracticality of real-time testing over a century, the industry instead relies on accelerated life testing met ..
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