The XD card is once considered as the thick and thin hood of Olympus and Fujifilm cameras. Olympus and Fujifilm introduced it in 2002 with the aim of transferring images faster from camera to PC. Alike to other camera cards XD card uses the same NAND flash technology instead of a flash translational layer it uses a facilitated Flash file system, which provides efficient data transfer of images to and from hard drives. The types of XD cards are M, M+ and H. Though there are three different types, the speeds for read operation is 6Mbps and write operation is 4Mbps. Unluckily, none of its type provides maximum transfer rate in both read and write operation. The M+ type leads in reading images while the H type tops in writing process. The interior structure of this type of cards is copy protected and never revealed by their manufacturers. At the raw level the XD card is same as the ordinary NAND flash integrated circuit but in a complicated package.
Declining factors of XD card:
If case you have formatted your XD card then, read here to know how to perform XD card recovery.