Bus Interface Specification has been integrated from High Speed (25MB/s) to 3rd Generation of Ultra High Speed UHS-III(624MB/s) to support high level data transition in between SD Host Devices and SD memory cards.
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. UHS-II and UHS-III host devices and cards can be attained such performance as well.