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SD stands for Secure Digital and as you may be able to guess, SDHC stands for Secure Digital High Capacity and SDXC stands for Secure Digital Extended Capacity. Although these cards are all the same size physically, they each make use of a different file format, allowing for progressively larger storage capacities.
SD is the older format that was the standard for most compact digital cameras and entry level DSLR cameras produced several years ago. The maximum capacity of an SD card is 2GB, which uses the FAT 12 or 16 file systems.
SDHC is a newer format that offers a maximum capacity of up to 32GB using the FAT 32 file system.
SDXC is an ultra-high capacity SD card format that uses the exFAT file system to offer storage capacity from 32GB to 2TB. 2TB is the theoretical limit, and the largest capacity currently available at the end of 2016 is 512GB, found in memory cards like the SanDisk Extreme PRO SDXC UHS-I Memory Card 512GB and the Lexar 512GB Professional UHS-I SDXC Memory Card.
Most newer cameras including compact cameras and entry-level DSLR cameras are compatible with SDHC and SDXC memory cards and your camera’s user manual and technical specs will be sure to mention which memory cards you can use. You can learn more about how memory cards work here and be sure to also check out our guide to choosing the best value per gigabyte when shopping for memory cards.