What Are SD Cards?

SD memory card is a new generation of memory device based on semiconductor flash memory. Because of its small size, fast data transfer speed, hot pluggability and other excellent features, it is widely used in portable devices such as digital cameras, Tablets and multimedia players.

MMC (Multi-Media Card,

SD Memory Card (Secure Digital Memory Card) is a

Digital embedded in SD card

The SD card interface, in addition to retaining the 7-pin of the MMC card, has also added 2 more pins on both sides as data cables. ^[3]

Viewed from above, there is usually a switch on the right side of the SD card, which is overwrite protection

SD cards are used in the following portable digital devices: ^[6]

Like other memory card formats, SD cards are protected by numerous patents and registered trademarks, and authorization can only be done by the Secure Digital Card Alliance. The license agreement of the Secure Digital Card Alliance in 2013 did not allow open source SD drivers. This situation has caused a lot of debate about open source and free software. The common practice is to develop an open source shell, but the core is a closed source SD driver for a specific platform, which is too different from the expected open standard. Another common practice is to use the older MMC mode, because according to the SD card standard, all SD cards must support the MMC mode. ^[7]

This shows that the SD card is less open than a CF card or flash memory. The above two formats are almost free, and only require an authorization fee to use the Alliance logo and registered trademark. But much more open than xD cards or memory sticks, these two formats do not provide public document support at all. ^[7]