BUYING GUIDE: Memory Cards

Memory card readers

If you've just bought a digital camera, you need a memory card. Or, memory cards, because you can never have enough memory.

Keep three things in mind:

1. Running out: The worst thing that can happen when you're on a photo excursion (besides a thunderstorm or a dead battery) is running out of space on your memory card (or to run out of cards).

2. Big files: Compact digital cameras these days produce at least 10MP files; many are in the 12-14MP range. DSLRs can produce images up to 24MP. And then there's HD video, which eats up memory like crazy.

3. Memory cards are very affordable. For instance, a 4GB CompactFlash card, which can hold hundreds of shots (depending of camera resolution), can cost between $20 and $100, and even less on special. Prices keep dropping. Buy as much memory as you can afford!

But memory cards are not just about capacity. If you're shopping for a memory card for your digital camera, you also must consider type and speed.


There are two main memory card formats. One of these will likely fit a current camera.

Secure Digital (SD) and Secure Digital High Capacity (SDHC)
, is currently the most popular. It's are about the size of a postage stamp, but despite the tiny shape, SD cards offer high maximum capacity and outstanding performance characteristics. Secure Digital High Capacity (SDHC) is the newest flavor of SD card and is exactly the same size. However, while SD cards top out at 2GB, SDHC cards can hold as much as 32GB. Older digital cameras that accept SD cards may not operate with SDHC cards; most new SD digital cameras are SDHC compatible.

Compact Flash (CF) cards provide the largest maximum capacity of all cards (up to 8Gb) and are used most often in digital SLR cameras and other cameras that produce large image files. They are available in two styles: Type I (the more common) and Type II. The difference is the card's thickness. Type I cards are 3.3mm thick and Type II cards are 5mm thick. It's usually possible to use a Type I card in a Type II slot but not the other way around. The Microdrive is the same form factor as CF Type II but isn't really a CF card at all. Instead of Flash memory it stores image files on a miniature hard drive. Microdrives are available in large capacities and are often less expensive that comparable CF cards. (See our product spotlight on Microdrives for details)

There are also a couple of proprietary card formats. Their use is fading as companies adopt CF or SD formats for newer cameras.

Memory Stick, Memory Stick PRO and Memory Stick Duo are usually found in Sony products, although a few other cameras use them. Memory Stick Pro version offers high capacity (up to 4GB) but cannot be used in some older Sony cameras, so be careful if you own a Cyber Shot S85 or another older model: you must use the original Memory Stick product.

xD Picture Cards: Older Fuji and Olympus cameras use xD cards (and a few accept both xD and Compact Flash). Even older models of these brands used SmartMedia, another format that's almost extinct, so check your owner's manual.


That's the big question, and there's no firm answer. Different cameras create different-sized files (even if two cameras say they shoot 8MP images, the final file sizes can still vary from one camera type to another. Users can change the compression ratio setting (sometimes called "quality") on your camera and that has very dramatic impact on the number of images a card will hold. The amount of detail in a scene can also affect image size if you are shooting JPEGs. Finally, if you shoot RAW format the image files will be very large.

This chart will help you get the idea.


The main reason one 4GB memory card costs more than another is its speed, or data transfer rate. The faster the card, the more you'll pay. You need a fast memory card if...

  • You shoot sports, news, or other fast-paced events where you'll be shooting a lot of pictures in a short time
  • You shoot HD Videos
  • You use your camera's burst mode (which lets you shoot up to several frames per second)
  • You shoot a lot of large RAW images
  • You are using the card in an advanced Digital SLR

You don't need a fast memory card if...

  • You mainly shoot snapshots and family photos
  • You use a compact camera (some compacts may have fast read/write speeds, so check your camera's manual before you buy)
  • You use a starter DSLR (Unless you're shooting HD Videos)

Memory card speed refers to how fast the card can write (store) and read (play back) image files. In general, faster cards will allow you to capture images and play them back faster than possible with a slower card. But before you go out and buy the fastest card on the block, consider the kind of camera you have and what kind of pictures you take with it. Some cameras don't have the internal circuitry to take advantage of fast cards, and using a faster card in a slower camera is a waste. In those cases, it's better to save a few bucks and buy an average-speed card.

How can you tell what is fast and what is average? Some manufacturers use the "X" notation. It's the same standardized measurement method that's used to rate the throughput of CD and DVD writers, and works as follows: 150KB per second is "1X" and all other speeds are expressed as multiples of that standard. Therefore, 40X means a write/read speed of 6Mb/sec (150Kb X 40 = 6,000Kb or 6Mb). 40X is fast. 60X is faster.

Others simply list the actual specification. For example, the label might say that the card can write and read at 20MB per second. Cards that can sustain sequential read and write speeds of 20MB per second are the fastest in their class.

SD card users may be further confused by a "Class" system. Class 1 and 2 cards are slow but fine for low-end compact cameras. Class 4 is the minimum you should use if you're shooting VGA-quality video, but these cards go as high as Class 10, which is fast. You'll appreciate the difference if you have a lot of big files to download.

Compact Flash Cards are available in up to 600X speeds, but 40-90X is typical; the faster cards are designed for high-end pro cameras where super-fast burst rates need to be maintained, or when shooting full HD video. In compact cameras where performance isn't an issue, slower cards (which cost less) are fine.


Memory cards shouldn't be mishandled, but they do hold up very well to normal everyday use. Never bend or twist them, and don't get them wet. Don't get the electrical contacts dirty and never try to open them. The biggest danger a memory card faces is getting lost. Keep them in a case when not in use.

Memory card cases offer protection from dirt and impact--and they're easier to locate in the bottom of a gadget bag. Cases are available in various configurations and materials, and some have compartments to carry spare batteries as well. You'll never regret the few bucks you invest in a card case.

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