The design between the SD , SDHC, and SDXC are very similar, and they can physically fit between devices however, Secure Digital standards are backward but they are not forward compatible. What this means is that a device that supports only the SD standard cannot read or write to an SDHC card, but a device designed for SDHC cards can read and write to an SD card. The SD extended capacity, or SDXC, standard supersedes SDHC. SDHC devices can't read or write to SDXC cards, but SDXC card readers can read and write to both SD and SDHC cards.
The primary different between the types of the Secure Digital is the capacity caps of the specific types.
SD standard - Up to 2GB SD memory card using FAT 16 file systems
SDHC standard - 4GB-32GB SDHC memory card using FAT32 file system
SDXC standard - 64GB-2TB SDXC memory card using exFAT file system
Please note that the file system found on these drive may vary.