What is SDXC? Is SDXC compatible with existing SD/SDHC devices?

XC is the newest SD standard. It supports memory capacities above 32GB up to 2TB. Devices (cameras, video cameras, computers, etc.) that are compliant to the SD Physical Layer and File System 3.00 version specs can support SDXC memory cards as well as SDHC and SD memory cards.

No. Existing SD and SDHC devices are not be compatible with new SDXC memory cards, but existing SD and SDHC memory cards will still continue to be offered by card manufacturers for the foreseeable future. Existing SD and SDHC memory cards will work in SDXC devices.