Data in an SD card is stored on a series of electronic components called NAND chips. These chips allow data to be written and stored on the SD card. As the chips have no moving parts, data can be transferred from the cards quickly, far exceeding the speeds available to CD or hard-drive media. The NAND chips in an SD card do not wear out easily, so data can be written to them thousands of times over their lifetime, making SD cards resilient and long-lasting in use.