When SD cards are manufactured they inevitably have failed sectors. This is why when you put a 4GB card into your PC it may read 3.89GB or some such, the 0.11GB represents the dead stuff. All of these dead sectors aren't necessarily next to each other, they are spread all over. When the card is manufactured, they test it to check how many dead bits it has, they then class it by these, a higher class having less dead bits. This isn't entirely important when transferring files, as a computer will skip the dead bits and crack on with the one after it no problem. The reason cameras, or cheaper and smaller electronics suffer is that they don't deal with dead sectors properly, they just want to write from start to finish and not take the time to work out if the sector has successfully taken the write. That action costs processing, thus increases the cost or size of the device. So, by specifying that you have to use super amazing class cards, they avoid having to increase the device cost on their side Now it's worth remembering that if you buy a high class card from china for cheaps, it's likely not going to be actually any good, you need to go for a reputable brand and you can even run a test on it once you open it, and if you find it's not satisfactory you could even contact them to ask what the deal is with their crap product. Run this tool on it https://www.avforums...w.1347842/��And it'll tell you it's speeds and it's actual capacity. Simply put, don't buy cheap @*!# SD cards from fleabay.
Sorry for the wall of text