The Speed Class Rating is the official unit of speed measurement for SD Cards, defined by the SD Association. The Class number represents a multiple of 8 Mb/s (1 MB/s), and metes the least sustained write speeds for a card in a fragmented state.These are the ratings of some currently available cards: * Class 0 cards do not specify performance, which includes all legacy cards prior to class specifications. * Class 2, 2 MB/s, slowest for SDHC cards. * Class 4, 4 MB/s. * Class 6, 6 MB/s. * Class 10, 10 MB/s.Even though the class ratings are defined by a governing body, like Χ speed ratings, class speed ratings are quoted by the manufacturers but inverified by any independent evaluation process. In applications that require sustained write throughput, such as video recording, the device may not perform satisfactorily if the SD card's class rating falls below a particular speed. For example, a camcorder that is designed to record to class 6 media may suffer dropouts or corrupted video on slower media. On slower class cards, digital cameras may experience a lag of several seconds between photo-taking, whilst the camera writes the picture to the card.