The SD Memory Card or Secure Digital was introduced in 2001 by SanDisk Corporation, Matsushita (Panasonic) and Toshiba. The SD Memory Card was based on the MultiMediaCard, MMC, memory card standard and has almost the same form factor, the size of a postage stamp, the only differences are that the SD memory card is slightly thicker and has a write protection switch. Since MMC cards are thinner than SD Memory Cards they can be used in all SD Memory Card slots but not vice versa.



The SD Memory Card is today the most common used memory card. It can be found in most digital cameras, PDAs and in many other electronic devices. The SD Memory Card slots can be used for more than flash memory cards. The SDIO, Secure Digital In & Out, is the general name for the many expansion modules that can be found in the SD Memory Card’s form factor. SDIO modules can be inserted in the slot and be used for other functions like Bluetooth adapters, GPS receivers, digital cameras, TV tuners, etc.

The SD Memory Card was the first memory card to be introduced in the Secure Digital family, which today consists of three members. In 2003 the miniSD format, 60 % smaller than the SD Memory Card, was introduced as the second member in the Secure Digital family. In 2005 the microSD was introduced as the third and the smallest member in the Secure Digital family. Since both miniSD and microSD come with an adaptor, they can be used in all SD Memory Card slots. Buy always the smaller format if you have electronic devices that support the SD Memory Card format and any other smaller format from the Secure Digital family.