Classes of SD Cards

• The class of an SD card is determined by its constant "writing speed," which determines how fast it can transfer data. The speed classes, Class 2, Class 4, Class 6 and Class 10, refer to the minimum number of megabytes per second at which the card can write. For example, a Class 4 card writes at 4MB per second.
  
  

High-Speed Cards

• The higher the speed class, the more expensive the card. For a consumer-level digital camera, a Class 2 card will w You should use a Class 4 or 6 for HD recording. SD Cards work similar to your computer's disk space. As you use up memory on your SD card, files can become fragmented. Faster SD cards handle fragmentation much better than lower-speed cards because your device can defragment them much faster; this is usually done automatically.
  
  

Low-Speed Cards

• Obviously, lower-speed cards are cheaper and designed for those shooting video on cellphones and standard-definition cameras. For the same price, a lower-speed SD card will have much more storage space, allowing you to save more information before having to download your photos and videos to a computer. If you upgrade to an HD camera, however, you will have to buy a compatible card, especially if you are using a Class 2 or 4 card. Class 6 is right in the middle and works with SD and HD recording.
  
  

Ultra High-Speed Classes

• The Ultra High-Speed (UHS) Class 1 card works at speeds up to 312MB per second and is designed for real-time recording and large HD video capturing. UHS Class and the normal Speed Class are not comparable measures of performance.