Secure Digital Card

Secure Digital, or SD, is a format of flash memory card based on Toshiba's earlier Multi Media Cards (MMC). SD is slightly thicker, and includes features that allow the secure exchange of data, enabling usage restrictions to placate copyright holders. It has essentially replaced MMC outright. It had been said that Secure Digital cards would become ubiquitous, replacing diskettes, but since has failed to do so. Its price is still prohibitively high, costing more and holding less data then its main competition, the larger Compact Flash.

Palm has made Secure Digital its preferred form of expandability for its line of PDAs. Other Palm-based vendors have followed suit. SD is fairly well supported in the digital camera industry as well, used in all Kodak cameras. It's also the memory of choice in some of Nokia's higher end cell phones, such as the N-Gage and the 36xx series. Olympus also produced some cameras with SD capability, but abandoned it in favor of its own solution--xD-Picture cards.