Some of our readers are asked “what is SD card class, and how to define SD card class?” Definition of SD card class: SD card class mean a write speed of an SD Card. It is define only by its writing speed and not the reading speed. Writing speed is a time that needed by SD card to store the data while file transfer is in progress. SD card classes apply on all SD card shape and size, either SD card, mini SD, micro SD, etc.
SD card class divided into several classes. The most common used are SD Card Class 2, SD Card class 4, SD Card Class 6 and Class 10. As far as we know SD class 10 is the highest class that available today. Above SD class 10, there is SD Card UHS Class 1 (UHS=Ultra high speed). So, if you find SD card class 12, especially made by the manufacture that you never heard before, you should be careful. SD Card Class 2 means it has a write speed at least 2 MB/s (2 MB per second); SD Card Class 4 has a minimum write speed of 4MB/s and so on.
To make it easier for you to understand about writing speed, we give you an example. If you want to transfer 100 MB file from computer to the SD card, when you use SD card class 4, it takes approximately 100:4 = 25 s (second). If you use SD card class 2, then the time required is 100:2 = 50 s (two times longer).
However, the transfer speed is also affected by the device hardware and/or the medium that connect the device with the SD card. For example, if you want to transfer files from computer to the micro SD class 4 that located in your phone using a data cable, then the data cable quality could affects the writing speed. Although the SD card has a high write speed, but if you used bad quality data cable, then it will reduce the write speed.
How to recognize the SD card class?
There still quite a lot of electronic sellers who don’t know SD Card class mean. Therefore, you need to know how to recognize the SD card class based on your visual. Usually, SD card class information is written on the SD card box and also in the SD card bodies. Information about SD card class is written by a SD card class number inside the letter C that is shaped almost like a circle. Below is the sample of SD card class 6 symbols. If the SD card is class 10, then the numbers written are number 10.
Many of SD card class 2 don’t give information about its class, so, if you can’t find the SD card class symbols, then probably the SD card is a SD card class 2 or the class has not been determined or standardized.
Just for your information, SD card class 2 could be having fast read speed, up to 15 MB/s or more. Therefore, many mobile phone users that previously use SD card class 2 then switch to SD card class 6, not much noticing the different in their phone performance. Because the read speed among SD card class 10 and the SD cards that has class below it, could be not much different. As we said above, SD card class is define by its write speed not their read speed. Read speed is the time needed to read the data stored on the SD card. For example, the time needed to load all picture that stored on the picture album of your phone.
The point is if you want to buy SD card for your phone and you feel the SD card with high class number is too expensive, then it’s not that necessary to buy SD card with high class number, especially if your phone is mid-low end phone. Because the phone performance is mainly affect by SD card read speed (not write speed), which is based on my personal experience, the read speed is not so much different among classes (unless the class gap too far, for example class 2 vs. class 10). However, if you have extra money, we suggest you to buy SD card with high class number, you probably still can use the SD card when you change your phone anyway.
If you want to buy SD card to use on your digital camera or video recorder, then we highly recommend you buy SD card that have high class number. Using low SD card class number on digital camera will increase delay time to take from one shot to another. The delay time is caused by the time to save picture (write data) to SD card. If you use it on video digital recorder, it can make the video unsmooth, full of lag, even in some case, you won’t be able to record the video.