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. The Secure Digital standard was introduced in August 1999 as an improvement over MultiMediaCards (MMC). The Secure Digital standard is maintained by the SD Association (SDA). SD technologies have been implemented in more than 400 brands across dozens of product categories and more than 8,000 models. The Secure Digital format includes four card families available in three different form factors. 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. There are many combinations of form factors and device families, although as of 2013, the prevailing formats are full- or micro-size SDHC and full or micro SDXC. The SDA uses several trademarked logos to enforce compliance with its specifications and assure users of compatibility.