The market for flash memory was over $20 billion in 2006, more than 34 percent of the total semiconductor memory market. Companies like Sandisk are continuously innovating both technology and package designs to create new markets for NAND memory chips. SanDisk makes flash storage devices that are used in removable cards, USB drives and are also hardwired into other products.
Most SD cards are shipped preformatted with the FAT or FAT 32 file system.
For flash memory cards, the average number of writes before failure occurs is usually above 100,000 times and always getting better.
xD cards are NAND flash chips in a special 18-pin package design.
SDHC (Secure Digital High Capacity, SD 2.0) is an extension of SD increasing card storage capacity up to 32 GB. You always want to look for the SDHC logo to make sure you are getting high capacity.
Secure Digital Extended Capacity (SDXC) format was unveiled at CES in January 2009. SDXC cards have a maximum capacity limit of 2 TB or 2,048 GB.
USB Flash Drives at Wikipedia for the technically inclined.