Speed class of a SD/Micro SD card is the Minimum guaranteed Writing [Obviously read speed will be higher than it] speed of a card denoted in MBps. It will be printed on the Micro SD card inside a partial circle.
Class 2 = 2 MBps Min Speed
Class 4 = 4 MBps Min Speed
Class 6 = 6 MBps Min Speed
Class 10 = 10 MBps Min Speed
[PS: There is No class 8 ]
It's often a misleading concept to choose a storage expansion for your phone based on the memory capacity only. When it comes to Smartphones , speed class plays a crucial role in the phone performance.Having a higher Read & Write speed card have advantages like games load faster , gallery images & Videos pops up faster , Camera clicks are saved in no time, Less delay between seeks in movie videos and lot more.Consider a game which loads a 50Mb data into memory.In a low class card it takes around 5+ secs ,while it takes 2 or 3 secs in a higher speed class card .
Higher speed class cards are more pricier than same low class capacities.In fact a class 10 card costs nearly double that of a class 4 card of same capacity . A class 10 card doesn't mean that the write speed is exactly 10MBps. Its only the min speed guaranteed [Single File Write ] in any environment. Actual speeds will be even higher.Personally i am using a Transcend 8GB Class6 card bought 2 years back and its offering a Speed of 10 MBps Write and 14 MBps read .
Most commonly Micro Sd cards are available in Class 4 . But there are Class 6 & Class 10 cards available from various manufactures like Sandisk , Transcend ,Kingston , Samsung ,Verbatim ,Strontium etc. Its always better to try the real world speeds before you choose between brands ,because the actual speeds may vary between various brands .You may also check with the manufacturer's website for the rated speeds.
Sandisk is offering ultra High speed cards Rated UHS offering read speeds as much as 30MBps and Extreme Pro cards offering a blazing 90MBps Write/95MBps Readspeed .
Coming to your Sony device , people are often confused by the capacities to choose from.Here is what i recommend .
Music,Ebooks & Photos - 8GB
+ lots of Videos -16GB
+ lots of Movies - 32GB
Phone as a portable storage - 64GB
Since Memory card is a long life accessory there's nothing wrong if you invest more on it.But keep in Mind that the prices are falling rapidly.So before you shop for a memory expansion for your Smartphone next time ,Make sure you check the speed class rating of the card.
:-)
