Understanding Memory Cards


So you’ve got your camera, and now you’ve got to figure out where all those photos are going to be stored. There are tons of options for organizing and storing photos once they’re taken, but we’ll get to those another time. For today, let’s take a minute (or five) to go over the myriad options available for memory for your camera. Sandisk, Lexar, Promaster, Kingston, and literally dozens of other companies make memory cards, and to further confuse the issue, there are several types of cards (SD, SDHC, SDXC) and classes of cards (Class 2 through Class 10). Most cameras currently use SD or XD cards, although a handful of holdouts still rely on Compact Flash cards, sometimes alone but other times in tandem with SD. Since SD is used in far more cameras, I’m going to leave CF to someone else; there’s a great explanation of CF cards here: http://www.compactflash.org/faqs/faq.htm In the meantime, let’s see if we can make heads or tails of the SD situation.

Let’s start with the types of cards. SD (technically SDSC, where the SC means Standard Capacity) simply stands for Secure Digital. The “Secure” part comes from the fact that it’s non-volatile memory (it doesn’t have to be powered up to store something). SDHC is SD High Capacity (4MB to 16MB), and SDXC is SD eXtended Capacity (32MB to 2TB). You might be tempted to buy a 2TB card or two (it would, after all, be the last time for a long time that you’d need to put a new card in your camera). Before you do that, bear in mind that things can, and do, go wrong with SD cards. Having something go wrong with a 2TB card means losing an awful lot of your work in one fell swoop, so it can sometimes be advisable to buy several smaller cards and switch them out frequently; if something goes wrong during a shoot, you’ll still have something left.

Having looked at the types of cards, let’s take up speed versus class. Loosely speaking, the card’s speed rating is its top speed, and is a concern mostly when it comes to burst shooting. Just the same as your car may be capable of 120 miles per hour, however, you’re not going to drive it that way all the time. Just the same as your car has a cruising speed, the card’s class is the sustained write speed for which it’s rated. So a class 4 card should be able to write 4MB/second for sustained periods of time (this is especially relevant in video recording, where the write speed has to be sustained for minutes at a time, versus short bursts).

Speed ratings and class can be a bit deceiving. As with anything else, your setup is only as strong as its weakest link. So let’s say you’re using a Class 10 SDHC card, which is capable of writing 10MB/second. Pretty fast. However, your camera may only have a write speed of 4MB/second. No matter how fast the card is, the camera has other things in mind. Conversely, if your camera’s native write speed is 10MB/second and you use a Class 2 card (2MB /second), it’s going to be slow going even though the camera’s fast; in essence, the card can’t keep up.

And of course, there’s an added wrinkle, which is your camera’s buffer. Let’s say your camera is capable of 7 frames per second, and has a 56MB buffer. If you’re shooting low-quality JPG images that might come in at 1MB each, you can hold that button down ’til the cows come home and you won’t have to worry about your camera freezing up on you (what you’re doing to your shutter is something else altogether). If, on the other hand, you’re shooting high-quality JPGs (which, for the sake of the example, let’s say are 5MB each), it’s only going to take you about a second and a half to fill your buffer. Your camera’s going to slow down while the buffer’s full, and will only allow shots again once the buffer has room for them. If you’re shooting RAW, the buffer will fill faster still because of the larger file sizes. In this case, the camera’s acting sluggish not because your card’s too small, too slow, or a piece of junk, but because you got a bit overzealous with the burst shooting, so this is something that’s probably best saved for times when it’s vital. If, like me, you tend to double up on shots (I do this if I’m shooting unsupported at slow shutter speeds, just because I’m more likely to get one that’s in focus), just be sure to keep your bursts small and evenly spaced.

In any case, read the fine print. In this case, that means two sets of fine print. First, know your camera. If it’s rated for Class 6, get a Class 6 card; a lower class will cause bottlenecks, and the camera won’t write any faster if it’s using a Class 10.* Second, know your cards. Don’t cheap out on a card that’s classed lower, and try to avoid off-label brands. Third, use brands recommended by the camera’s manufacturer, as they typically recommend higher-quality cards that won’t fail you at an inopportune time. Failed cards mean lost photos, and even if you can use a data recovery program, that’s no guarantee you’ll get all of your photos back, or that the files won’t be corrupted. Finally, regardless of the card you’re using, make sure that the first thing you do is to format it when you first use it with your camera so that the camera “recognizes” the card and puts it to its best use.

Any questions, or anything I’ve left out? Feel free to comment!

*Let me add a caveat: if you’re getting some kind of discount for buying cards in volume and you have more than one camera, then by all means, buy with the higher-specced camera in mind so you can safely use the same card in both (just make sure you’re using the correct format for the cards). There’s nothing wrong with buying nothing but Class 10 if you simply have to have the best and fastest of everything, but your camera may not need the added speed.

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