Have you been in a situation looking for your next SD card, comparing different brands and models, and trying to choose the best for your needs? Then you realize that on some of the SD cards you see the speed in MB/s, on others you see it with the “x-rating” (like 633x, 1000x, 2000x). Furthermore, some cards have shown the speed class number (usually nowadays it is C10), and some have a U1 or U3 sign. Some are marked with SDHC, and other SDXC I or SDXC II. And some cards have V30, V60 or V90 on them… So what do all these numbers mean?