The Secure Digital (SD) card is fully compliant with the standards released by the SD Card Association. The Command List supports [Part 1 Physical Layer Specification Ver6.1 Final] definitions. Card capacities of non-secure area and secure area support [Part 3 Security Specification Ver3.0 Final] Specifications.
The SD card has a 9-pin interface, designed to operate at a maximum frequency of 208MHz. It can alternate communication protocol between the SD mode and SPI mode. It performs data error detection and correction with very low power consumption. The Card capacity could be more than 64GB and up to 512TB in the future with ex-FAT file system, which is called SDXC (Extended Capacity SD Memory Card).
Secure Digital cards are one of the most popular cards today due to its high performance, good reliability and wide compatibility.