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junior member

Reged: 02/05/08
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SD speed: class vs. X rating
      #29562 - 02/05/08 05:39 AM

Trying to compare the speed of SD cards. When the SD card says 50X, 100X, 133X, etc. what is X?

I understand that only SDHC cards are rated by class, and that class may be calculated differently than the X speed rating. Is there any general speed estimate for the classes?

Is there any way to generalize and compare the speed of SD cards rated with X and SDHC cards rated with class?


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Reged: 07/11/02
Posts: 8574
Loc: Texas
Re: SD speed: class vs. X rating [Re: carlzzz]
      #29567 - 02/06/08 02:19 AM

Unfortunately, there is no standardization as to what the "x" rating means across brands of cards. Kingston states that "x" refers to write speed, where x= 150 KB/sec, so their 120x card has an 18 MB/sec. transfer speed. But other manufacturers don't necessarily use the same formula.

With SDHC cards, the class rating doesn't have a translation to that mystery x value in non-HC cards. But the higher the class, the faster the card-- and there are at least specs for classification of cards by class .

Lisa Gade
Editor in Chief, MobileTechReview

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