$10 price drop. Best Buy has the SanDisk SDSDQY-064G-A11A Mobile Ultra 64GB microSDXC Class 6 Memory Card for $40 with free shipping. Features up to 30MB/sec data transfer rates, Secure Digital adapter, and Sandisk Media Manager software.
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Tax and class 6 kill the deal for sure.
class 6 is good enough for music and cell phone.
30MB/sec data transfer rates, why then only Class 6 ???
^ because of the minimum write speed, though I think these might actually be class 10 cards not 6 unless they're old stock.
I have trouble deciphering what is meant by "up to" xyz transfer speed. Does it guarantee the xyz speed and if not, what is the max guaranteed speed? And what is the min speed?
There is often the claim that class speed is "worst case scenario" but this is not true. Worst case would be concurrent small mixed writes while what they really mean is continuous streaming mode like you'd see with single stream video recording.
Often I read the text "miniumum guaranteed... not a sustainable rate", but that is exactly what it is, the minimum sustainable rate to remove the factor of host buffering on devices like single shot cameras.
Thus, if it's a class 10 card as I speculate, it should at the least support a 10MB/s video stream write from a camcorder, or similarly at least 10MB/s continuous write from a computer with an adequate card reader.
There is no max speed guarantee, though generally if a card performs above a certain class number across an acceptable % of the yield, it will be rated for a higher class speed. Generally speaking you can expect the max write to stay under 20MB/s with SD cards in most consumer equipment.
Regarding reading instead of writing, for large sequential reads of a class 10 card you can usually expect the host device or bus used to be the bottleneck rather than the card. 30MB/s is often specified while some may see less from slow equipment or some a little more with a good USB2 or especially USB3 card reader and host USB chipset - again in consumer equipment, the cards themselves can be capable of more for a price premium.
While I don't find the class ratings entirely honest, they are still fairly useful in situations where a device needs a minimum or higher real-time sustainable write speed to function properly. In real world uses that's more helpful than the prior "up to" (nnn)X speed rating standard that SD cards used to have.
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@dave_c,
The Lexar white paper on SD Class is very informative. Thanks.