In general SD cards are only capable of storage up to 2GB, although higher capacities are available up to 4GB, they tend to run into compatibilty issues. SDHC (Standard Digital High Capacity) will have a minimum capacity of 4GB. Because of the increasing market in high-definition video and high-resolution digital photography, the demand for an SD card to hold more data became a neccessity. SDHC cards are categorized into write speed classes. The higher the class, the faster the card writes. SD and SDHC are not cross compatible, devices that only support SD cards will not be compatible with SDHC cards. However, if you have a device that supports SDHC, you can use an SD card but not vice versa.