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I purchased a SanDisk 32 GB microSDHC Flash Memory Card SDSDQM-032G nearly two months ago, for use in my VIZIO 8-Inch Tablet VTAB1008. At the same time, I also purchased a higher-priced PNY 32 GB microSDHC Card (P-SDU32G10-EFS2) which is supposed to be a 'class-10'. My benchmark results, however, show that the Sandisk class-4 card is actually faster most of the time.
I used two sets of benchmark programs. One is called 'Flash Memory Toolkit v2.0', which measures the random read/write speed of files between 1MB and 15MB. The other one is called 'H2testw v1.4', which measures the sequential read/write speed using 1GB files. Here are my results: (see my uploaded charts in 'Customer Images' section for details)
For smaller files (1-5MB), the Sandisk class-4 card gives an amazing write speed of 15-17MB/s, while the PNY 'class-10' card can only get 1-6MB/s
For larger files (10-15MB), the Sandisk and PNY cards are about equal at around 8MB/s for write
For huge files (1GB), the PNY did better at 9.5MB/S, while the Sandisk dropped to 5.5MB/s
The read speeds of both cards are equally high at around 18MB/S (this number may be limited by the maximum speed of my card reader used)
What the above shows is that: When used in a typical digital camera (with file size 3-5MB), this Sandisk 'class-4' card is at least twice as fast as the PNY so-called 'class-10' card. But when used in a HD video camera (sequential writing of huge file), then the PNY card should perform better.
For a card to be marketed as a 'class-10', it must maintain a MINIMUM write speed of 10MB/s. So by this definition, the PNY card does not qualify since it cannot even achieve a MAXIMUM write speed of 10MB/s. This Sandisk card, on the other hand, exceeds the requirement of 'class-4' by a huge margin.
Sandisk seems to be the only flash memeory manufacturer that still gives honest, conservative speed class ratings. Any other manufacturers would have labeled this card a 'class-6' or even higher. As a matter of principle, I rather give my money to a company that promises less but delivers more, instead of to others that do the opposite. At the present cost of about 1 buck per GB, this is an unbeatable deal!
[Aside]
The capacity of this card, as reported by my computer, is only 29.7GB. Note that this is actually normal, because compter people define one 'Giga' as '2 to the power 30', which is 7.4% greater than 1 billion. So 29.7GB comes to just about 32 billion bytes, which is '32GB' according to marketing people.
[Update Dec 3, 2011]
I re-tested the two cards above, using the CrystalDiskMark v3.01. The results are consistent with my previous finding. See my newly uploaded charts in 'Customer Images' for details.
[Update Nov 19, 2013]
The Sandisk card is still working fine after two years in my tablet. It should be noted that I have purchased dozens of CF/SD/microSD cards over the past decade, and only experienced ONE card failure (which was caused by an incompatable card reader). So I'm probably just more careful in handling memory cards. For example, I always make sure to discharge myself electrically before touching a card to avoid ESD zap, and use "Safely Eject USB Device" command to remove a card.
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