Updated: September 17, 2014 2:29 PM
By Régis Jehl

The sensors in digital cameras are getting bigger, and so are the size of files captured onto memory cards. The type of memory card you use can often be as important as the camera itself—especially if you don't want to spend ages moving your photos around.

These days, it's difficult to leave the house with just a single 2 GB SD card in your camera.  Now that larger SDHC cards are available in sizes up to 16 GB, which ones are the fastest?  And what about the new ''Class'' system for identifying the data transfer rate of the various new cards?

SDHC—or High Capacity SD cards—are ideal for owners of digital cameras that have 10 Megapixels or more.  With a single JPEG image weighing in at 5 MB, and JPEG+RAW files approaching 20 MB, it's very easy to fill a 2 GB SD card.

Bigger cards, new standards

The SDHC standard currently allows for cards of up to 16 GB, with the promise of 32 GB cards in the future.  Compared to the classic SD, the SDHC also has a new system for classifying cards according to how fast they transfer data.  No more X's—say 'hello' to the three new 'Classes': 2, 4 and 6.  These guarantee minimum speeds of 2, 4 and 6 MBps, respectively.

In practice, the three classes are well-respected by manufacturers, although there is sometimes a tendency to over-estimate speeds.  However, as usual, a few products stand head and shoulders above the rest—to such an extent that today it seems necessary to enlarge the class system as far as Class 14 or higher.  In our tests, some cards reached speeds of up to 20 MBps, but are still counted as 'Class 6' because they reach at least 6 MBps.

In fact, while most memory cards usually surpass their specification speeds by several MBps, some cards have write speeds that really outpace the competition.  For example, the Class 6 PNY Optima SDHC 4 GB offers a maximum of 10.33 MBps, while the overachiever at the moment, the ATP ProMax 4 GB, also a Class 6 card, offers no less than 15.57 MBps when writing large files.

SD and SDHC: not to be confused!

Unless your memory card reader specifically offers support for SDHC cards, it may not be able to read them.  SD cards and SDHC cards may look the same, but only certain readers are capable of accessing the newer SDHC cards.  Remember that SD cards are only ever 2 GB or smaller, so if you have a card that's 4 GB or larger, then it has to be an SDHC card and you'll need an SDHC-compatible card reader.
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