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Secure Digital CardSecure Digital (also known as SD) is a flash memory memory card format. SD cards are based on Toshiba's older Multi Media Card (MMC) format, but add little-used DRM encryption features and allow for faster file transfers, as well as adding a bit of thickness. Devices with SD slots can use the thinner MMC cards, but SD cards won't fit into the too-small MMC slots. Standard SD cards measure 32mm by 24mm by 2.1mm. Typically, an SD card is used as storage media for a portable device, in a form that can easily be removed for access by a PC. For example, a digital camera would use an SD card for storing image files. With an SD reader (typically a small box that connects via USB or some other serial connection), a user could copy the pictures taken with the digital camera off to his or her computer. Modern computers, both laptops and desktops, often have SD slots built in. SD cards are currently available in sizes up to and including 2 GB, and are used in almost every context in which memory cards are used, and in nearly every application, they are the most popular format. SD support is standard in PDAs, with Dell, PalmOne, HP, Toshiba, Sharp, and others including SD slots in all of their PDAs. Digital cameras (including Kodak's cameras) tend to support SD cards, as well, although Olympus and Fuji (with xD cards) and Sony (with Memory Sticks) favor their own proprietary formats, and many professional cameras support Compact Flash in addition to or instead of SD, to allow pro photographers to use multi-gigabyte microdrives. SD cards can also be found in flash-memory-based mp3 players, GPS trancievers, the occasional cell phone, and occasional portable game systems. SD is the currently the most popular flash memory card format, as older competitors like Multi Media Cards and SmartMedia cards are marginalized at best and obsolete at worst. Some of the long-time competitors have found other niches, however. Compact Flash support is mostly limited to older devices and professional-quality digital cameras (which mostly include CF support to allow the use of microdrives), and Memory Sticks failed to have find any success outside of Sony's dogged support in their own devices. Like most memory card formats, SD is covered by numerous patents and trademarks, and licensing is only available through through the Secure Digital Card Association. The SD Card Association's current licensing agreement doesn't allow for open-source SD drivers, a fact that generates a fair amount of consternation in the open-source and free software communities. The usual workaround is to develop an open-source wrapper for a closed-source SD driver available on the particular platform, but this is far from ideal. A recent development, pioneered by SanDisk but quickly copied by other companies, are SD cards with built-in USB plugs, to eliminate the need for an SD/USB adapter or SD slot on a PC. The high cost of these special SD cards and the ubiquity of SD readers makes it unclear how successful these SD/USB cards will be. The signature "SD" logo was actually developed for another use entirely: it was originally used for "Super-Density Optical Disk", which was the unsuccessful Toshiba entry in the DVD format wars. This is why the "D" looks so much like half of an optical disk. SDIO SD slots can actually be used for more than flash memory cards. Devices that support SDIO (typically PDAs, but occasionally laptops or cell phones) can use small devices designed for the SD form factor, like GPS receivers, WiFi or Bluetooth adapters, or digital cameras. See Also The SD card isn't the only flash memory card standard ratified by the Secure Digital Card Association. Other SD Card Association formats include: External links
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