Definition: SD card

(Secure Digital Card) A family of flash memory cards available in two sizes: SD and microSD. Introduced in 1999 by Panasonic, Toshiba and SanDisk, and managed by the SD Association, the SD card superseded the MultiMediaCard (see MMC). Capacities have reached 1TB. See microSD and flash memory.

The full-size SD cards are widely used for storage in stand-alone digital cameras. The small microSD cards have also been used for storage in smartphones. However, many vendors dropped that option, requiring customers to choose the built-in storage at time of purchase.

For video recording, SD cards support various write speeds, and although they were designed for copyright protection (the S in SD means Secure), they were not widely used for security (see CPRM and SD card classes). See Video HD, Eye-Fi and SDIO card.

SD Express - More Speed
In 2018, SD Express added support for additional interfaces and higher speeds while keeping backward compatibility (see SD Express).

microSD - miniSD - SD

The microSD card (left) obsoleted the miniSD format. Adapters let microSDs plug into full-size SD slots (see microSD). (Images courtesy of SanDisk Corporation.)

   SD     Year                File
 Format   Into   Capacity    System

  SD      1999     1-2GB     FAT16
  SDHC    2006     2-32GB    FAT32
  SDXC    2009  32GB-2TB     exFAT
  SDUC    2018   2TB-128TB   exFAT

More Speed and Capacity

The newer HC, XC and UC formats added more speed and capacity. All new SD slots accept older cards as well. See FAT32 and exFAT. (Images courtesy of SanDisk Corporation.)