xD stands for eXtreme Digital. It was developed by Olympus and Fujifilm, who introduced it to the market in July 2002. The Toshiba Corporation manufactures the cards for Olympus and Fujifilm. Other brands, including Kodak, Silicon Power, SanDisk, and Lexar, sell xD picture cards also.
xD cards are currently available in these capacities: 16MB, 32MB, 64MB, 128MB, 256MB, 512MB and 1GB (Type M). An xD card is 20mm × 25mm × 1.78mm and weighs 2.8 grams. The 16MB and 32MB models write at 1.3mb/s and read at 5mb/s. The 64MB, 128MB, 256MB and 512MB models write at 3mb/s and read at 5mb/s. The 1GB (Type M xD card) model writes at 2.5mb/s and reads at 4.0mb/s.
The Type M was released in 2005. It uses Multi Level Cell (MLC) architecture to achieve higher storage capacity than the 512MB. Although Type M capacity will eventually stretch to 8GB, the 1GB card is currently the only card in this range.
The xD format primarily competes with formats such as Secure Digital Card (SD), CompactFlash (CF), and Memory Sticks. xD cards are fast in comparison with formats such as SmartMedia (SM), MultiMediaCard (MMC) and MemorySticks (MS), but xD picture cards are much slower than the main competitor SecureDigital (SD).OpticsPlanet, Inc offers a full line of original xD-Picture Memory Cards with full manufacturer's warranty and Free Shipping on orders over $29.95!

xD-Picture Memory Cards by Brand

SanDisk xD-Picture Memory Cards

Silicon Power xD-Picture Memory Cards