The xD-Picture Card, is flash based memory card that is used mainly in digital cameras. The "xD" itself stands for "extreme Digital". Fujifilm and Olympus introduced the memory card into the market in July of 2002. The Toshiba Corporation and Samsung Electronics now manufacture the actual cards for Olympus and Fujifilm. Recently, other brands have gotten into selling xD cards, including Kodak, SanDisk, and Lexar.
Besides being used in Olympus and Fujifilm digital cameras and Olympus digital voice recorders, Fujifilm also makes an MP3 player that uses the card. As of the end of 2006, there are xD cards available in 16 MB, 32 MB, 64 MB, 128 MB, 256 MB, 512 MB, 1 GB, and 2 GB capacities.
The original xD cards were available in 16 MB to 512 MB capacities. In February 2005, the Type M card was released which used "Multi Level Cell (MLC)" which allows for a storage capacity of up to 8 GB. The Type M cards are on sale from 256 MB to 2 GB capacities but they suffer from slower read-write speeds than the original cards.
In November 2005, the Type H card was released and promised higher data rates and larger capacity. The Type H cards sell in the 256MB-2GB capacities. The type H cards are necessary in newer model cameras to Capture video at a high rate (640x480x30).
The type M and H cards have compatibility issues with older cameras, but full compatibility lists are available from Fujifilm and Olympus. Some card readers also have troubles reading the new types.
Pictures are transferred to the computer by either using a USB cable or by inserting the card itself into a memory card reader.
The xD format was created to compete with other memory card formats such as Secure Digital card (SD), CompactFlash (CF), and Sony's Memory Stick.
A couple advantages of xD cards are their small size, faster speeds than some other formats, and use low power consumption.
A few disadvantages of xD cards are that they are much slower than the market leader SecureDigital, they are usually more expensive, and can only be used with Fujifilm and Olympus.
xD has been losing more and more market share to SecureDigital as time continues on due to its higher cost and limited use.