MicroSD Card classes - what we need to know

[NetCom]

SD cards are rated by class (not just MicroSD) though it is not mandatory for manufacturers to include this information on SD cards. It is mandatory on SD/SDHC cards however (which includes many MicroSD cards).

Basically, the classification system lets you know the guaranteed minimum operating speed of a SD/SDHC card. The classes are 2, 4 and 6 (as of now), though Samsung just announced a product which would qualify as a hypothetical Class 8.

A Class 2 means a card with a speed of 2 MB/s or higher is guaranteed at the best fragmented state where no memory unit is occupied.
A Class 4 means a card with a speed of 4 MB/s or higher is guaranteed at the best fragmented state where no memory unit is occupied.
A Class 6 means a card with a speed of 6 MB/s or higher is guaranteed at the best fragmented state where no memory unit is occupied.

Be sure that you know what the requirements of the device that you will be using this card with before making a purchase. Many GPS units and phones which use SD cards will say for example, that a card with a Class rating of 4 or better is required...

(copied from source: Yahoo answers)

[marstein]

It would still be interesting to see if the controller on the device can actually use the speed. In some cameras it doesn't matter how much bandwidth the card has because the camera cannot use it.