[OB] SDHC Card speeds

[Charlie Smith]

Earlier, Charlie Smith wrote:
> 
> > Make sure you get at least a class 6 card, this is a measure of speed.
> > There seems to be some smoke & mirrors on SD card speeds.  I see
> > 20x, 133x, 15MB/Sec, Class 4, class 6, ????
> > I don't have a Rosetta stone top translate 20x to MB/Sec, or to class ?.
> > Does anyone have this scoped out?
> 
> The few references I've seen are -
> 
>     a 15MB/sec card was Class 4
>     a 20MB/sec card was Class 6 and referred to as 133x.
> 
> This is the best 32Gb card I've seen so far (but way too expensive for me):
>     http://www.dpreview.com/news/0801/08010806panasonic32gbsdhc.asp

Here's information I've found on SDHC card speeds.  First, this URL
has more information on SD in general than you will ever want to know:

    http://en.wikipedia.org/wiki/Secure_Digital_card#Speeds

SDHC cards have SD Speed Class Ratings defined by the SD Association. 
The SD Speed Class Ratings specify the following minimum sustained 
MByte/Sec write speed on to empty SDHC cards:

    * Class 2:  2 MB/s
    * Class 4:  4 MB/s
    * Class 6:  6 MB/s

I understand that read speed *may* be significantly faster than 
write speed.  And you note the above specifies "empty SDHC cards".
I have not yet found anything speaking to speed loss for non-empty
cards.  If you want more on the 133x type speed descriptions, read 
the above URL. 

And if you've wondered what was meant by "Secure Digital" (SD), 
you may be interested to learn that the secure comes from being
SDMI-compliant (Secure Digital Music Initiative) - as pushed by
Recording Industry Association of America (RIAA).

    - Charlie