I recently ordered a “Class 10” 32 GB MicroSD card PNY, (exact model 32GB Hi-Speed MicroSDHC Class 10 for Tablet PCs P-SDU32G10TEFM1) and replaced the old 8 GB class 2 stock Samsung card in my HTC EVO 4G (here’s how to upgrade a microSD card). Although I’m happy with the extra space I got, I’m a bit disappointed with the writing speed which in my case doesn’t match the class 10 specifications and requirements. It should be above but it is way under 10 MBps.
Multiple tests with the SD Tools Android app on my HTC EVO (CyanogenMod 7.1) report around 7.5 MB/s which is only about 2.5 MB/s higher than the results I was getting from the original class 2 Samsung card (yes, it was giving me great 5+ MB/s performance).
You may say the problem is in my phone (I thought so, too), but then I tested it on my laptop (one year old) using the included SD adapter (more details below) and that test gave me similar results – just under 8 MB/s writing speed, As far as my tests are showing, this is a class 6 card. No problem with reading speed, but no passing grade for a class 10.
The math of the laptop test is as folows:
I used a large zip file (so there’s no cheating on compression/decompression) on my laptop and it took 5 mins 14 s to copy 2,624,746,942 bytes (2.44 GB or 2503.15 MB) from hdd to microsd. Divide the MBs transferred (2503) by number of seconds (314) and you get your speed – just under 8 MB/s.
The phone tests measured at different times throughout several days gave me these results in Writing/Reading speeds [MB/s]:
Average write/read speed on the phone: 7.5/20.4 MB/s. In my book that would be a solid Class 6. Anything above is cheating.