08-17-09 02:32 PM
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  1. bt224's Avatar
    From the wiki..

    SD Speed Class Ratings

    SD Cards and SDHC Cards have Speed Class Ratings defined by the SD Association. The SD Speed Class Ratings specify the following minimum write speeds based on "the best fragmented state where no memory unit is occupied":[7]

    * Class 2: 2 MB/s - 13x
    * Class 4: 4 MB/s - 26x
    * Class 6: 6 MB/s - 40x

    SD and SDHC cards will often also advertise a maximum speed (such as 133x or 150x) in addition to this minimum Speed Class Rating. Important differences between the Speed Class and the traditional "X" speed ratings are; 1) the ability of the host device to query the SD card for the speed class and determine the best location to store data that meets the performance required, 2) class speed defines the minimum transfer speed. Even though the class ratings are defined by a governing body, like "X" speed ratings, class speed ratings are quoted by the manufacturers but unverified by any independent evaluation process.
    08-17-09 02:32 PM
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