SD card technology is based on multimedia card format. The data transmission speed of SD card is relatively high, and the standard is constantly updated. Most SD cards have write protection control on the side to avoid accidentally writing some data, while a few SD cards even support digital rights management technology.
The size of SD card is 32mm×24mm×2. 1mm, but the official standard also records the "thin version" thickness of 1.4mm, which is the same as MMC card. SD card is sometimes called memory card in Chinese, but this "memory card" and "memory" are actually two completely different concepts.
Extended data
Like other memory card formats, SD card is protected by many patents and registered trademarks, and authorization can only be carried out by SD card association. The current authorization agreement of SD card association does not allow open source SD driver, which has caused a lot of arguments about open source and free software.
The usual practice is to develop an open source shell, but the core is a closed source SD driver for a specific platform, which is quite different from the expected open standard. Another common practice is to adopt the older MMC mode, because according to the SD card standard, all SD cards must support MMC mode.
This shows that SD card is less open than CF card or flash memory: these two formats are almost free, and only need to use the licensing fee of the alliance logo and registered trademark. However, the openness of SD card is still much higher than that of xD card or MS, and these two formats do not provide public file support at all.
Baidu encyclopedia -SD card