4GB SANDISK/TRANSCEND MICRO SD/SD MEMORY:Secure Digital (SD) is a nonvolatile memory card used extensively in portable devices, such as mobile phones, digital cameras, GPS navigation devices, handheld consoles, and tablet computers. It is a family of solid-state storage media.
It is the smallest memory card that can be bought; at 15 mm × 11 mm × 1 mm (about the size of a fingernail), it is about a quarter of the size of a normal-sized SD card. There are adapters that make the small microSD able to fit in devices that have slots for standard SD, miniSD, Memory Stick Duo card, and even USB. Asymmetrical slots in the sides of the SD card prevent inserting it upside down, while an MMC goes in most of the way but makes no contact if inverted. Most SD cards are 2.1 mm (0.083 inches) thick, compared to 1.4 mm (0.055 inches) for MMCs. The SD specification defines a card called Thin SD with a thickness of 1.4 mm, but they are rare, as the SDA went on to define even smaller form factors. The card's electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user's fingers. The SD specification envisioned capacities and transfer rates exceeding those of MMC, and these have both grown over time.