SD High-Capacity CardsFaster Storage, More Capacity, Greater FlexibilityThe SD High-Capacity (SDHC) card provides more removable storage power than ever before. With a capacity range starting at 4GB and going up to 32GB, developers have the choice to specify three data-writing speeds at guaranteed minimum data transfer rates.
The SDHC card, already a market leader in the digital camera marketplace, preserves photographic integrity and raises the memory performance bar by guaranteeing minimum — more important than maximum — performance rates. This large capacity is essential for use with a variety of digital content types — especially with high-quality video. 
In addition, many photo printers, card readers, video cameras and other devices are also equipped for SDHC guaranteed transfer rates, demonstrating the trend toward SDHC memory card leadership. SDHC-enabled products accommodate SDHC memory cards and are backward compatible with SD memory cards. Data on SDHC cards is protected even if inserted in an incompatible device. SDHC cards also work in standard SD slots with a firmware upgrade.
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The SD Association has established a new specification rating for the minimum data transfer for standard and high-capacity cards, as well as both types of host products. With the new Speed Class specifications, the host product can check the fragmented state in the card and calculate the write speed in each part of the card. The host can then determine where to write the data according to its speed requirement. The three SDHC speed classes - Class 2, Class 4 and Class 6 - transfer data at least 2, 4 and 6MB per second.