When it comes to SD (Secure Digital) cards, there’s something called a “Speed Class Rating”. On NewEgg for example you can peruse cards based on this specification:

The higher the number, the better the speed, which means a 10 is the best you can get.
A question however is does this even matter when connected to a smartphone running Android?
Yes, it does.
The speed class of an SD card affects two things with an Android phone. File transfer speed and boot-up time.
Concerning transfer speed, this is dependent on the phone’s processor speed and memory, but you will notice a difference. How much difference depends on the hardware you already have.
Concerning boot-up time, this can be measured in seconds easily. The difference between a Class 2 and a Class 6 for example can be as much as 3 seconds, with the 6 obviously being the better of the two.
If you’re thinking to yourself, “3 seconds? That’s not significant.” It is when you’re waiting for your phone to boot.
Is there a big cost difference between classes?
Not really. With 8GB models for example, you’ll normally find the higher classes only cost a few dollars more. On the 16GB end I only saw a one-dollar difference between similar classes.
If you can, always go for the higher class. Your file transfers will be quicker and boot-up times faster. You’ll appreciate the faster boot time more than anything else.

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I’ve read that android is capped at class 2 or 4, but I haven’t seen any facts to support that. Can you confirm android can benefit from a class 10? If not, is it a hardware or software issue which could be updated by Google later? Thanks in advance.