The SD Association Defines SDXC and SDHC Standards
With new SD cards coming out regularly and new features being added, there's got to be a way to keep track of what's what. It's especially important once your card is out of the packaging. It's frustrating to look at a pair of cards and try to figure out which one's got the nice high transfer speeds.
Two new symbols have been introduced by the SD association to clear up the confusion.
Cards with an Ultra High Speed (UHS) rate of transfer will be marked with the USH-I symbol, which is simply a capital I located on the right side of the card next to the letters HC or XC. This symbol designates the card as capable of transfer rates of up to 104MB a second.
The other symbol, which designates Speed Class 1, marks cards that are intended for real time high definition video recording. The marker for this is a number 1 inside of a U, also on the right side of the card, but next to the letters SD.