MicroSD

SD, SDHC, SDXC

SD (top), miniSD, microSD cards
Media type	Memory card
Capacity	SDSC (SD): 1 MB to 2 GB,    some 4 GB were made SDHC: 2< GB to 32 GB SDXC: 32< GB to 2 TB
Developed by	SD Association
Dimensions	Standard: 32.0×24.0×2.1 mm (1.260×0.945×0.083 in) Mini: 21.5×20.0×1.4 mm (0.846×0.787×0.055 in) Micro: 15.0×11.0×1.0 mm (0.591×0.433×0.039 in)
Weight	Standard: ~2 g Mini: ~0.8 g Micro: ~0.25 g
Usage	Portable devices, including digital cameras and handheld computers
Extended from	MultiMediaCard (MMC)

Secure Digital (SD) is a non-volatile memory card format developed by the SD Card Association (SDA) for use in portable devices.

The standard was introduced in August 1999 by joint efforts between SanDisk, Panasonic (Matsushita Electric) and Toshiba as an improvement over MultiMediaCards (MMC), and has become the industry standard. The three companies formed SD-3C, LLC, a company that licenses and enforces intellectual property rights associated with SD memory cards and SD host and ancillary products.

The companies also formed the SD Association (SDA), a non-profit organization, in January 2000 to promote and create SD Card standards. SDA today has about 1,000 member companies. The SDA uses several trademarked logos owned and licensed by SD-3C to enforce compliance with its specifications and assure users of compatibility.

There are many combinations of form factors and device families, although as of 2016, the prevailing formats are full or micro size SDHC and SDXC cards.

Secure Digital includes four card families available in three different sizes. The four families are the original Standard-Capacity (SDSC), the High-Capacity (SDHC), the eXtended-Capacity (SDXC), and the SDIO, which combines input/output functions with data storage. The three form factors are the original size, the mini size, and the micro size. Electrically passive adapters allow a smaller card to fit and function in a device built for a larger card. The SD card's small footprint is an ideal storage medium for smaller, thinner and more portable electronic devices.

The second-generation Secure Digital (SDSC or Secure Digital Standard Capacity) card was developed to improve on the MultiMediaCard (MMC) standard, which continued to evolve, but in a different direction. Secure Digital changed the MMC design in several ways:

Full-size SD cards do not fit into the slimmer MMC slots, and other issues also affect the ability to use one format in a host device designed for the other.

The Secure Digital High Capacity (SDHC) format, announced in January 2006 and defined in version 2.0 of the SD specification, supports cards with capacities up to 32 GB. The SDHC trademark is licensed to ensure compatibility.