Olympus and Fuji have developed their own ultra-compact digital camera memory card. It's called the xD card, and “xD” stands for “eXtreme Digital.”
xD cards are particularly notable for their size. Even smaller than SD cards, these tiny cards are barely larger than a penny, but have a theoretical capacity of up to 8 GB. (Currently, 1 GB is the largest capacity available.)
Two types of xD card are available: Type M and Type H. Type H cards are slightly faster writing data from your camera, and also offer special picture effects that can be used with some models of Olympus camera.
The same caveats that apply to Memory Stick media apply here. They limit camera choice and aren't as readily available as CF or SD cards.