We are deciphering the specification markings that you’ll find on SD and microSD cards such as SDHC, SDXC, 128GB, C2, C4, C6, C10, UHS-II U3, V30, V60, V90, A1 and A2. The next time you are in the market, you’ll know exactly what you are purchasing and if it will fit your needs.

Capacity
One of the first markings you’ll see on any SD or microSD card is capacity. This is how much storage space this particular card has available. You’ll pay more to get more storage, but bigger isn’t always better. Check your device’s manual to find which capacity is compatible with the device and shop accordingly. After that, you may see a marking saying SDHC or SDXC. These are two newer classifications of SD card noting that the SD cards have higher capacities. SDHC cards have capacities ranging from 4GB-16GB while SDXC cards can store 64GB and higher. These are newer types of SD cards, so while newer devices may support older SD card formats, an older device may not be able to support the newer formats. Good to keep in mind.

Read/Write Speed
The read and write speed of the card might be shown this as megabytes per second or MB/s. Others may show different speeds for read and write or even show speed as a number followed by an x. Higher speeds are important for specific cameras and video cameras.

Speed Classes
Now Speed class is something different entirely - a bit confusing I know but stay with me on this one. Speed class refers to the minimum sustained write speed. You’ll normally find this on a card shown as a symbol with a number surrounded by a C. The higher the number, the higher sustained write speed the card is capable of, with C2, C4, C6 and C10 representing a minimum write speed of 2, 4, 6 and 10MB/s respectively. If your camera or drone is taking full HD video, you will want a higher speed class.

UHS Speed Class
Then there’s UHS speed class, which you’ll find on a card marked by a 1 or 3 inside a U. This is a marking found on the newer SDHC or SDXC cards and also provides the minimum write speed of a card. UHS Speed class 1 has a minimum 10MB/s speed and UHS Speed class 3 has a minimum 30MB/s. A card with the U1 or U3 marking also means it uses one of several UHS bus interfaces, indicating the theoretical maximum read and write speeds which are different from the sustained speeds of speed classes we’ve discussed up until now. You will see UHS bus interface shown as roman numeral I, II or III.

Video Speed Class
There’s also video speed class, which you’ll find on cards specifically optimized for video recording. This is marked by a symbol that looks like a V followed by a number showing the minimum write speed in MB/s. V10 and V30 are good for 1080p content, V60 for 4k and even all the way up to V90 for 8k. With all of these speed class marking options, you may see a card that says both U3 & V30 - even though they both mean the same thing. Good to be thorough I guess.

Redundant Specification Labels
Even more confusingly, you may see a card that says U3 and V30 and C10. But if C10 means 10MB/s and U3 and V30 mean 30MB/s, which is it? The answer is the higher of the two. As the SD Association, which is the organization responsible for naming SD cards, kept adding new speed classes, memory manufacturers try to include as many designations as possible to help customers find the right card. For example, if your new camera says it needs a C10 card, but the SD card only uses the newer U3 marking, you might not know that this card will work with your new camera. If it says both C10 and U3, more bases are covered, albeit a bit redundant.

App Performance Class
If that wasn’t enough, there is another specification called App Performance Class. This is a newer classification that came about with Android’s Adopted Storage Device feature. However, this expandable memory feature seems to be on the decline in new Android device and it may be short lived. App Performance Class shows that a card has the minimum random read and write speeds to both store and run apps as well as hold more traditional phone data like pictures, videos, files, etc. If a card meets these qualifications you’ll see a small A1 or A2 2. A2 is 3-4 times faster than A1 in its random read and write speeds. Both A1 and A2 have a sustained minimum write speed of 10MB/s.
Hopefully by now, these markings are starting to look a little less like an ancient alien language and a bit more like something that you’d feel confident navigating. If there are any other markings you’ve found on a card that you’d like to tap the hive mind here at Kingston to help decipher, leave em in the comments below.

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