Secure Digital (SD) is a type of memory card commonly placed in portable devices. These cards provide fast data access and can be purchased at a reasonable price. They come in three form factors: (in order of decreasing size) SD, miniSD, and microSD.

A Raspberry Pi computer uses a microSD card to store its operating system and data. Therefore, almost every Raspberry Pi should be purchased along with an microSD card, without which the device is unable to function.