An SD (Secure Digital) card is a small flash memory card that is used to provide high-capacity storage in a compact size. They are widely used in mobile devices such as smartphones, audio players, handheld computers, digital cameras and digital video camcorders.
Scandisk, Toshiba and Panasonic first introduced the SD card in 1999 and it quickly became the most popular choice for digital camera storage. SD cards utilize flash memory to provide a form of nonvolatile storage that does not require a power source to retain data once it has been saved. The have also become a popular choice for small portable devices because they have a high data transfer rate and a low battery consumption.
A standard SD card is roughly the size of a postage stamp; it is 32 mm by 24 mm and weighs about two grams. A mini SD card is 21.5 mm by 24 mm, while a micro SD card is 15 mm by 11 mm.
SD cards have an encryption feature known as key revocation that allows users to securely store copyrighted material. They are also less prone to damage because they only use metal connectors as opposed to traditional plugs and pins. Due to their smaller size, mini SD and micro SD cards require an adapter before they can be used with general purpose SD readers.