- The definition of an SD (Secure Digital Memory Card) card is a small card for creating more memory on a digital camera, cell phone or other portable device.
An example of an SD card is a memory card used in a digital camera to allow more images to be held in memory.
(Secure Digital Memory Card) The most popular flash memory card for digital camera and other mobile storage. Introduced in 1999 by Panasonic, Toshiba and SanDisk, cards up to 128GB are available with huge capacities planned for the future (see SDXC below). SD Cards use the same 32x24mm form factor as the earlier MultiMediaCard (MMC), but are slightly thicker (2.1mm vs. 1.4mm), and SD Card readers accept both formats. Fast Storage Although SD Cards support encryption and content protection (the "Secure" in SD), they have been mostly used for regular storage due to their small size and fast transfer rate, which started out at 10 MB/sec and has steadily increased. SD uses NAND flash technology (see flash memory). Smaller: miniSD & microSD Introduced in 2003 and 2005 respectively, the small-footprint miniSD and microSD formats are electrically and software compatible with the regular SD Card. They can also plug into full-size SD slots via adapters (see microSD). SD High Capacity (SDHC) Based on the SD Card Association 2.0 specification, SDHC cards do not work in SD devices, because SD uses the FAT16 file system, and SDHC uses FAT32. However, SDHC devices support both SDHC and SD Cards. SDHC also comes in miniSDHC and microSDHC formats. See Video HD. SD Extended Capacity (SDXC) Introduced in 2009, and available up to 128GB, SDXC cards raise the future maximum capacity to two terabytes (2TB) by using the exFAT file system. SDXC cards are compatibile with SDHC. A microSDXC format is also available. See Eye-Fi, gruvi card, SDIO card and MultiMediaCard. UHS-I and UHS-II In 2010, the Ultra High Speed (UHS-I) interface was introduced for SDHC and SDXC cards at 104 Mbytes/sec. In 2011, UHS-II tripled the rate to 312 MB/sec to support reading and writing high-resolution 3D HD content.