Because of the variety of high-performing and feature-rich devices in the market, there is a demand for higher performance SD memory cards. The SDA has introduced a higher bus interface with higher theoretical read and writing speed specifications for the SDHC standard and SDXC standard.
|Bus Interface||Card Type||Bus Mark||Bus Speed||Spec Version|
|Normal Speed||SD, SDHC and SDXC||---||12.5MB/s||1.01|
|High Speed||SD, SDHC and SDXC||---||25MB/s||2.00|
|UHS-I||SDHC and SDXC||50MB/s (SDR50, DDR50)
|UHS-II||SDHC and SDXC||156MB/s
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.
Although normal-speed cards and high-speed cards can be used in UHS-I and UHS-II host devices, the conventional performance levels of UHS-I supported host devices can only be attained with UHS-I memory cards, and the conventional performance levels of UHS-II supported host devices can only be attained with UHS-II memory cards.