SD, SDHC Abbreviation
SD is an abbreviation of Secure Digital, a memory card format used in digital cameras and other electronics.
SD memory cards, based on the SD Specifications Version 1.01 and Version 1.10, have a capacity of 2 GB or less, although 4 GB non standards-compliant cards can be found. The 1.01 cards have a maximum transfer rate of 10 MB/s (66x, 1x=150 KB/s), whereas the 1.10 compliant ones are rated at 22.5 MB/s maximum (150x).
SDHC is short for Secure Digital High Capacity, which is based on the SD Specifications Version 2.00. The SDHC memory cards have capacities that can range from 4 to 32 GB, although theoretically they can reach 2 TB, or 2000 GB. SDHC cards also support transfer rates up to 150x.