A SD card will normally work in a SDHC device (possibly with lower performance). SD cards are in the following capacities 4,8,16,32,64,128,256 512MB and 1GB, 2GB only. Currently mainly 2GB SD cards are being sold.
A SDHC card will not work in a SD device such as a camera or reader. SDHC cards are in the following capacities 4GB, 8GB, 16GB and 32GB
SDHC (Secure Digital High Capacity) was established to meet the growing demand for HD (High Definition) video and high resolution image recording now used in many SD-enabled devices.
SDHC is the same physical size and shape as standard SD but meets the new SD specification of version 2.0. If the SD card is 4GB or above, it is classed as a SDHC card. Currently, SDHC specifications allow for memory cards of a capacity between 4GB and 32GB.
SDA (SD Card Association) has also established a Speed Class rating (Class 2, 4, 6 and 10) for the standardisation of data transfer speeds (compulsory for SDHC cards):
* The minimum speed capability depends on the manufacturer of the host device and model.
All Class 2, Class 4, Class 6 and Class 10 SDHC cards are compatible with SDHC devices. Please note that if the device manual suggests a SDHC card of speed Class 4 as a minimum, the user should install a Class 4, Class 6 or Class 10 (faster) SDHC, NOT a Class 2 card as this may reduce performance of the device.
SDHC cards are not backwards compatible with standard SD devices, so they may not work in digital cameras or USB Memory Card Readers manufactured before summer 2007.
Most new devices that require the new SDHC format to operate will display the SDHC logo on the product (such as printed on the side of a camera casing) and/or user guide.
Standard SD Cards will work in SDHC compatible devices such as Memory Card Readers. In a SDHC camera a standard SD may be of limited use due to the slower read and write speed of this older technology.
The information contained in this FAQ also applies to microSD and new microSDHC plus miniSD and new miniSDHC formats. The only difference will be the physical size of the memory cards, the speed class information and compatibility issues are the same.