SD is the abbreviation of Secure Digital and is one standard of memory card. It is widely used in the portable devices, such as digital cameras,PDA, mobile phones and multimedia players. The technology of SD is based on the MMC format, but the SD card is thicker than MMC . There is higher speed for data transmission,and also changing the standard frequently . The profiles of most SD cards set the anti-wirte control to avoid writting the data accidently, less of the SD cards supports the technology of DRM. The SD card provides different speeds through the method of 150KB/s of CD-ROM as one times speed to count . Basically, its transmission speed is more 6 times900KB/sthan the normal CD-ROM, the high-speed SD card can transmit 66x10 MB/sand 133x or higher speed.