Definition:
SDHC memory cards are a type of SD memory card that are capable of holding between 4GB and 32GB of data. These cards have the same physical shape and form factor as SD cards. As a result, SD and SDHC cards are sometimes confused with one another.
It's important to remember that older devices may not support the newer SDHC format. However, SDHC cards are backwards compatible with SD cards. In other words, if your PDA accepts SDHC cards, you can also use SD cards in the handheld as well.