SDHC speed ratings

Bill V WA7NWP wa7nwp at
Thu Mar 18 22:31:17 PDT 2010

I picked up a 8 GB SDHC card at RS today for my little netbook.   I
choose the $25 class 2 device instead of the $55 class 6 device.   I
was a big curious to the difference and found the answer on wikipedia:

It would probably make a significant difference for compiling or
something - but not for playing John Denver...

Bill - WA7NWP

PS.  Wikipedia also notes the transfer rate for a standard hard drive
is 500 MBits/sec or better...   USB 3 - where are you?

Speed Class Rating

The Speed Class Rating is the official unit of speed measurement for
SD Cards, defined by the SD Association. It is equal to 8 MBit/s, and
it measures the minimum write speeds based on "the best fragmented
state where no memory unit is occupied":[8]

The following are the ratings of some currently available cards:

    * Class 2: 16 MBit/s (2 MByte/s)
    * Class 4: 32 MBit/s (4 MByte/s)
    * Class 6: 48 MBit/s (6 MByte/s)

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