Shopping around for a new MicroSD card for your BlackBerry? Totally confused about what the difference is between a Class 4 and a Class 6 device? Wondering what 133x or 66x or 32x means?
Turns out that it is quite simple. The class defines the minimum write speed for a completely empty SD card. That means if you were writing to a new SD card that has never had any data on it how fast would it write.
- Class 2 = 2 megabytes/second
- Class 4 = 4 megabytes/second
- Class 6 = 6 megabytes/second
So in short Class 6 is what you should be buying for fast write speeds. On top of this there is also the speed rating of the card itself. This is based on how fast the microSD card can READ the data off the card. You will see this usually described as 32x, or 66x, or 133x, or something with an x and the end. 
These measurements are based on the original CD-ROM drives which could write 150kb/second. So 32x means 32 multiplied by 150kb/second or 4.8MB/second. This nice little table from Wikipedia gives you a basic idea of what each one stands for in terms of speed:
| Rating | Speed (MB/s) |
|---|---|
| 6x | 0.9 |
| 32x | 4.8 |
| 40x | 6.0 |
| 66x | 10.0 |
| 100x | 15.0 |
| 133x | 20.0 |
| 150x | 22.5 |
| 200x | 30.0 |
Let me know if you have any more questions!
Chris Not Registered
Posted: January 12, 2009 at 4:48 PM EST
Thanks for the detailed info. I have an 8gb card in my Curve 8330. I don’t think a faster writing card would help. The curve still needs a faster processor
indroo Not Registered
Posted: January 12, 2009 at 6:14 PM EST
What the different between SD and SDHC in relation to the read and write speed of those microSD card?
myers6mm ( View Profile) Newcomer - Posts: 10
Posted: January 12, 2009 at 9:24 PM EST
I just read about this a week or so ago on Wikipedia, Here’s some more info http://en.wikipedia.org/wiki/Secure_Digital_card
myers6mm ( View Profile) Newcomer - Posts: 10
Posted: January 12, 2009 at 9:29 PM EST
Ok, nevermind my stupid comment! I just noticed the link in the article is the same as mine! Sorry!
Ronen Halevy ( View Profile) Senior admin - Posts: 5298
Posted: January 12, 2009 at 11:40 PM EST
No worries. Just trying to spread the knowledge. May do another one about the difference between SD card and SDHC and also the difference between device RAM and Device Storage
DavidB Not Registered
Posted: January 13, 2009 at 7:29 AM EST from my BlackBerry 9530
Right, but which Blackberry smart phones are capable of which Class is the question. If the device is only able to write at 2, spending the extra for a 4 or 6 is a waste, no?
Given price parity, of course just buy the faster. But it would be nice if RIM would upgrade their capacity FAQ by adding max write speed each hardware supports.
And don’t forget the new SDXC if you’re gonna write about cards!