About the xD Picture Card
xD stands for "extreme digital," promoting the fact that these mini digital memory cards could hold a lot of information. These cards were one of the varieties of competing digital storage formats developed primarily for use in the emerging digital camera market.
xD picture cards were used primarily in Fujifilm and Olympus cameras and MP3 players and were manufactured almost entirely by Samsung and Toshiba to support those Japanese brands. The picture card never developed beyond 2 GB of storage capacity (8 GB was the maximum capacity of the technology) and was phased out, with hardware support for the card being phased out as well, leaving xD picture card owners without a way to read data from them or store data to them, especially if they no longer have their camera.
Cameras that used xD picture cards would plug into a computer via a USB or Firewire port, allowing the computer to read the xD media directly from the camera.
If you have xD cards, want to use them and do not have your camera, you may have difficulty if your computer or card reader only accepts Secure Digital (SD) cards because an xD card adapter to SD card reader & writer is something that, quite frankly, does not exist.
Image Credit: Wikimedia Commons/D.328