The next key designation to understand is bus interface speed. SD and microSD cards in 2 GB and lower capacity points do not have designated speed classes, this classification begins at 4 GB with the SDHC Host Device. Cards that do not support UHS (Ultra High Speed) bus speed will simply have the SDHC, SDXC or SDUC logo. UHS enabled cards will have a I, II or III, depending on the supported bus speed of 104, 312 or 624 MB/s, respectively. UHS-I and non-UHS cards will have standard eight (microSD) or nine contacts (SD), whereas UHS II and III cards have a second row of contacts to enable this high-speed functionality. Ensuring the customer is utilizing a card with compatible speed designations to the design will maximize the performance of the card in the application.