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How Long Do Memory Cards Last?

Nothing lasts forever. And this includes the memory cards you use in your camera to record each precious image. Have I gotten you scared yet? Relax. The truth is a bit more complicated.

To understand what's going on here, we need to start with the basics of just what a memory card is. Whether we're talking about compact flash, SD card memory or something more exotic such as XQD, memory cards contain pretty much the same thing, a storage medium known as flash memory. This stuff is a close relative of the RAM your computer uses to run programs. But unlike computer RAM, flash memory is non-volatile. Remove the electrical power from your computer and it will crash. Turn off your camera with a memory card in it or pull that card out and everything will still be on that card, safe and sound so long as the camera had finished writing it. Non-volatile memory doesn't require a constant power source to retain its contents.

Flash memory was invented back in 1980 at Toshiba by Dr. Fujio Masuoka, although it would take at least another decade before commercial applications began appearing. Apart from obvious considerations such as the cost of any new technology, the primary limitation of flash memory relates directly to the reason why it's called "flash" memory. While it was possible to turn on individual memory bits and bytes, you could only erase them in bulk, by clearing a whole block together. This process reminded the inventors of the flash of a camera. Perhaps the inventors had a somewhat colorful imagination to make such an analogy, but I guess inventors have to be creative types, so we'll give them a pass. At any rate, this limitation created significant challenges if you wanted to use flash storage as a general use medium. Engineers developed complicated mechanisms for creating the illusion of byte-level rewrites by moving what you weren't deleting to a new block and then wiping the original block clean by flashing it.

One problem these engineers couldn't overcome was that each time a block got flashed to erase it, its ability to store new data slowly degraded. Flash memory can only stand so many program erase cycles before it stops working reliably. Newer and potentially more expensive flash memory can hold out longer, but most commercially available implementations will give up the ghost at around a hundred thousand program erase cycles. That may sound like a lot, but I bet neither you nor I are keeping count.

An additional limitation known as "read disturb" regards a tendency over time for read access to flash memory to inadvertently become programmed, thus corrupting their contents. To mitigate the problem, flash memory controllers track such reads and move the data to a new block before the inevitable happens. While this helps with the read disturb issue, it does create another reason why blocks have to be erased. And every erasure adds up. Eventually, that flash memory and the memory card it's contained within will fail. And even if the entire card doesn't fail, any part of it that does can potentially wipe out images you care about.

In the early days of digital cameras, the cost of flash memory was quite high indeed. We all used modest sized cards because bigger ones either didn't exist or weren't affordable enough to justify. The only alternative though was something called a micro-drive, invented by IBM. These were the same size and form factor as compact flash cards, but contained a tiny spinning hard drive about the size of a US quarter rather than flash memory. For the same cost, you could buy a micro-drive with much greater capacity than you could a solid state memory compact flash card. But micro-drives were extremely fragile. All it would take was a modest impact to ruin such tiny spinning disk platters. If you're worried about flash memory failing, you would have really hated micro-drives.


The makers of flash memory cards know well the challenges inherent in the technology, so they do their best to prevent problems. If your memory card fails, you're going to get mad at the company who made it, and they could lose sales if enough people get mad. They have all sorts of clever tricks to move the data on the card around to avoid areas likely to fail. But eventually, something bad will happen.

Don't bother trying to figure out exactly what your risk is. I know what some of you are thinking, and it won't work. Even if you could invest enough time and effort to calculate when your card will fail, you'd end up with little time left to pay attention to your photography. And then what would be the point of the memory card?

So, should you be proactive and chuck your card in the trash after some period of time, and then switch to a new card? Perhaps, but my guess is you won't really need to. At least I know I don't plan to. I will continue buying new cards for other reasons though.

The capacity and speed of new cards keeps me buying new ones periodically and I'm betting you're no different. My first compact flash card was a whopping eight megabytes. It came with an early Nikon CoolPix compact digital camera. Even with the small size of image files produced by that camera, it didn't hold very many images. By today's standards, I couldn't fit even a single image on that card, not because the card has changed, but because my camera has. Newer cameras create bigger files. For a long time, I got by with a pair of 512 megabyte compact flash cards. Those too have long since been retired. As the price per gigabyte for new memory cards continues to drop, convenience dictates that it makes sense to buy bigger cards. I'm in no danger of cards failing because I'm retiring older ones for reasons having nothing to do with programmed erase cycles or read disturb errors.

New flash memory drives for computers have the same inbuilt limitations. Indeed, the entire storage industry is moving in this direction. The days of spinning hard drives in computers is slowly drawing to a close as the affordability and reliability of compact flash hard drives improves. One day, spinning magnetic disk hard drives will be as rare as compact flash micro-drives for use in your camera.


Date posted: March 15, 2015

 

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