A constant writing speed class for video recording. There are three kinds of Speed Classes, “Speed Class”, “UHS Speed Class” and “Video Speed Class.” This Speed Class provide the constant speed necessary for video recording by designating a minimum writing performance, this include V6、V10、V30、V60 and V90. V6 Speed Class means that the minimum write speed of the memory card needs to reach 6MB/s, V10 is 10MB/s, 30 is 30MB/s, and so on.
V60 and V90 can be applied to high resolution and high quality 8K video recording, and V30 can be applied to 4K resolution.
SD makers will print these speed class symbols on memory card (V60, V90…etc.). These speed class symbols will be applied to SDHC, SDXC, UHS-I, UHS-II and SD memory card help users decide the best combination for reliable recording.
*Fonte: Associazione SD