SD bus speed of 12.5MB/s Default Mode was defined by SD1.0 and 25MB/s High Speed Mode was defined by SD1.1 to support digital camera.
Its high performance function for continuous shooting required higher write speed memory card where SD Association introduced higher speed bus interfaces for SDHC and SDXC memory cards named UHS-I, UHS-II and UHS-III.
UHS-I can provide ultimate bus speed using 1st Row pins. UHS-II and UHS-III have ability to provide much higher bus speed than UHS-I using 1st Row and 2nd Row pins. 2nd Row interface is supported with Low Voltage Differential Signaling (LVDS) technology.
|Bus Interface||Card Type||Bus Mark||Bus Speed||Spec Version|
|Default Speed||SD, SDHC and SDXC||---||12.5MB/s||1.01|
|High Speed||SD, SDHC and SDXC||---||25MB/s||1.10|
|UHS-I||SDHC and SDXC||50MB/s
|UHS-II||SDHC and SDXC||156MB/s Full Duplex
312MB/s Half Duplex
|UHS-III||SDHC and SDXC||312MB/s Full Duplex
624MB/s Full Duplex
Maximum speed differs from the bus I/F speed. It varies depending upon the card performance. The average speed that a device writes to an SD memory card may vary depending upon the device and the operation it is performing. The speed may also depend on how other data is stored on the SD memory card.