Original xD cards had storage capacities up 512MB (megabytes), or about 0.5GB (gigabytes). Type M and type H xD cards, released in 2005, increased potential storage capacity to 8GB, although most xD cards offer up to 2GB. Such cards have an "M" or "H" marked on the card. Type M+ xD cards appeared in 2008, offering better transfer speeds. Some older Olympus and Fujifilm digital cameras cannot use the type H, M+, or M cards.
Olympus and Fujifilm developed xD cards for their cameras, beginning in 2002. xD cards are slightly rectangular in shape, with one edge slightly curved. xD cards measure 20 mm by 25 mm by 1.78 mm (0.79 x 0.98 x 0.07 inches).