Lifespan of flash memory

Dear Control Engineering: It seems that more devices, including industrial controllers, are using flash memory to store and transfer data and programs. How long does this kind of memory last?

04/04/2010


Dear Control Engineering: It seems that more devices, including industrial controllers, are using flash memory to store and transfer data and programs. How long does this kind of memory last? Extending the question, is it safe for me to keep photos from my personal digital camera on CF and SD cards?

You’re correct that you are seeing such memory devices in more industrial applications. Recent products from Beckhoff, Fuji, and Siemens all use CF (compact flash) cards to transfer data.

Predicting lifespan is a very controversial area and there are many opinions on the topic, but one point of the discussion seems clear: the lifespan of a flash memory device is not determined by time as much as cycling. In other words, if you buy a new USB thumb drive and load a file on it once, it should last many, many years. Exactly how many is yet to be determined.

Once you get into cycle counts, the number also varies, but it seems that even the cheapest flash drive that uses multi-level cell memory is good for 10,000 write cycles. Better drives that use single-level cell memory are typically good for 100,000 write cycles. Unfortunately, you probably won’t be able to tell which you have. Once you exceed that number, the failure is not catastrophic, it’s incremental. Individual bits begin to fail and corrupt whatever files are associated with them. Some of the more sophisticated types have internal software that can bypass bad bits, but eventually it will catch up with you.

Given most industrial applications and your typical digital camera, such devices aren’t going to be written to that many times. You will more likely lose your data because someone physically breaks the card, misplaces it, or the connector wears out. Most connectors start to fail after 1,500 connection cycles.

There are experimental applications that are pushing the limits of flash memory, using it as a solid-state drive (SSD) to replace hard drives in servers. Even with the constant write cycling of such applications, such massive devices suggest life spans of easily 10 years, and perhaps more like 50 years, with no moving parts.

In any case, you should never trust any type of memory device completely. If the data is really important, back it up. That is always good advice.

–Peter Welander, process industries editor

Posted by Ask Control Engineering on April 3, 2010



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