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SD Card Class – What Does It Mean?

Monday, October 6th, 2014 by | Filed Under: Uncategorized

Michael from NY writes:

  I need to get a 32GB micro memory card for my tablet. I don`t understand what they mean by class 10, or class 4. Would you please explain about these cards?  Thanking you in advance.

 To give you an accurate answer, I went straight to the horse’s mouth to see what the SD card association had to say about the differences. After all, they should certainly know SD cards better than anyone. 

Basically it all comes down to transfer speed. Manufacturers use different types of flash memory to make the card. The class rating is designed to indicate the minimum writing performance to ensure smooth transfer of streaming content like videos.

You’ll see two kinds of speed designation.  Speed class is a number surrounded by a large C and Ultra High Speed Class is a number enclosed by a large U.


The speed glasses defined by the SD Association are Class 2, 4, 6 and 10.  These speeds apply to SD, miniSD, microSD, SDHC, miniSDHC, microSDHC, SDXC and microSDXC cards.

Ultra high speed class only works on specific devices designed to record video at this level.  They are not interchangeable with other cards. The USH Speed Classes are U1 and U2.

Any of these standard speeds should work well for transferring photos and documents.  Class 2 should be sufficient for recording in standard definition. Class 4 and Class 6 are sufficient for full HD video recording. Class 10 would enable you to record full HD video and also grab HD-quality still from that video.

 Device speed class requirements are the minimum choice for that device. A device that requires a Class 4 card will work with Class 4, 6 or 10 cards. If it requires a 6, it will work with Class 6 or 10.

The higher the class of the card, the less fragmentation you’ll see with write speeds for items like documents and photos. So a faster card will speed things up somewhat even if you aren’t recording video.

 Memory cards are amazing things. It’s hard to believe a card that’s the size of a fingernail like this  can hold 128 GB. That would be considered a pretty-good sized hard-drive in many computers. As someone who spent many years working in the television industry, I can’t tell you the difference having these cards to put into cameras has made in the weight of cameras and the ease of using them.

Another thing to keep in mind when purchasing your card besides the class is to make sure that the size of your card is compatible with your device. Many tablets will only accommodate up to a 32 GB memory card and some older cameras won’t take a card larger than 2 or 4 GB.  Also, some older devices won’t work with an SDHC card, but instead require an SD card. If you aren’t sure what type of card your device works with, make sure you check the documentation or the the manufacturer’s website before you purchase a memory card.

~ Cynthia

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