SD (Secure Digital) and SDHC is a removable flash memory card for storing data. Measuring 24 x 32mm with a thickness of just 2.1mm. They are a popular choice for digital cameras, video cameras, netbooks, MP3 players and other portable devices. There are various standards of this card which include SD, SDHC and SDHX. SDHC (Secure Digital High Capacity) is an extension of the SD standard. A SDHC card is the same physical size as an SD card, make sure your device can accept the HC standard. Classes 2, 4, 6, 8, 10 etc refer to the data transfer speed in Mbits/s.