SD memory cards have become the most widely-used flash memory card standard for digital devices. Now, there are SDHC cards that look just like SD cards. In this issue of Random Access, I'll discuss how this new card with a familiar look is trying to replace the older generation, and how that might just be a good thing.
The SDHC logo
SDHC cards are the big brothers to SD cards. The HC stands for High Capacity because capacities start at 4GB (the old SD card capacity limit) and go up to 32GB. SDHC cards are the same size and shape as the SD cards you're used to. The only way to know they're the HC cards is the label.
You can't have progress without some sort of growing pains. In this case, the new SDHC cards will only work with devices that are compatible. This means you need to check the specs of any camera, camcorder, MP3 player or card reader you want to use with an SDHC card. Rest assured, most newer devices will support SDHC. Also, SDHC devices are backwards-compatible with SD cards so you can use your old cards with new gadgets. If you have an older device that didn't come with SDHC compatibility, check the vendor's site for a possible firmware upgrade to get the device compatible with SDHC.
A Class 6 SDHC card
You may have seen
a class rating
of 2, 4 or 6 on SDHC flash memory cards. These are data rate speed classes. According to the
SD Association (the folks who set standards for SD cards),
an SDHC card's class specifies the "guaranteed minimum
data transfer rate" for the card.
A Class 2 card will transfer at least 2MB per second, Class 4
at 4MB and Class 6 at 6MB. Remember, these are minimum speeds. Maximum speeds, though not always advertised, are surely much higher.
Not content with the
32GB limit of SDHC cards, the SD Association just announced a new card format: SDXC (Secure Digital Extended Capacity). Initially geared toward the digital camcorder market, this new specification will allow up to 2TB (that's 2000GB) of data to be stored on the same-sized card. Look for SDXC cards and devices by early 2010.
SD & SDHC Cards