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What’s in an SD Card?

by Administrator Administrator ‎04-16-2015 10:23 AM - edited ‎04-22-2015 04:39 PM (2,320 Views)

SD CardOne of the most frustrating things you can come across when shopping for something is a grouping of strange symbols and letters on an item with no explanation for the differences. It’s like looking at the laundry tag on clothes items and being presented with 5 symbols with no reference “do I wash with cold water and then machine dry? Or wash in warm water and hang dry?” (By the way if someone could explain these to me I’d be forever grateful.)   In the electronics world an item you might come across like this is your standard everyday SD Card, but luckily we’re here to help explain these differences and get you the card that suits your needs best.











We’ll start off with the simplest difference. You may find some cards listed as SD, SDHC, and SDXC. These classifications are based on the size of the card. SD covers the range of cards that are up to 2 Gigabytes (GB) in size. SDHC (High Capacity) covers cards that are more than 2 GB and up to 32 GB in size. Finally SDXC (eXtended Capacity) covers card sizes that are greater than 32 GB and up to 2 Terabytes (TB) While there may be a new capacity class in the future, at this time SD cards have not been made available for consumers in sizes this large so these will most likely be only three for a while.


Speed Class:






The other most noticeable marking on the card would be the speed class. This marking denotes the minimum sustained transfer speed of data between the recording device and the card during video and will be the main stat you will want to consider for video recording or for cameras that support a burst shooting mode. Before choosing a card you’ll also want to refer to the packaging of your camera/recording device prior to choosing a speed class as it will typically list the minimum class you should choose as well as whether it is compatible with the UHS speed class.



Standard Speed Classes:


These are the speed classes that will support older cameras as well as cameras that are not compatible with HD video.


2Class 2: The lowest speed class. This will also be the assumed class if an SD card does not have a class marking on it. The minimum transfer speed for this class is 2 MB/s and is suitable for up to standard definition (480p) video recording.


4Class 4: Provides a minimum transfer speed of 4 MB/s and is the first class that is suitable for HD (720p 1080p) video recording.



Class 6:  Minimum transfer speed of 6 MB/s for shooting HD video at higher frame rates.



10Class 10: The highest speed class for non UHS compatible cameras and provides a minimum transfer speed of 10 MB/s. This speed class supports Full HD Video recording and is also suitable for HD still image continuous shooting.


UHS Speed Classes:


UHS (Ultra High Speed) speed class is denoted by a U with a speed class listed in the middle. While most UHS cards on the market do support a standard speed class as well as a UHS speed class it is best to consult your camera manual to verify compatibility prior to purchasing a UHS only card.


1UHS-1: The first level of the UHSBus speed. UHS-1 provides a minimum transfer speed of 10 MB/s and like class ten should be suitable for both full HD video recording as well as HD still image continuous shooting.



3UHS-3: Currently the highest speed level available for consumers. UHS-3 provides a minimum sustained transfer speed of 30 MB/s and is the first speed level suitable for 2k and 4k video recording.



Please keep in mind that while you may see higher transfer speeds listed on the box when shopping for a card, the class is important as it is the minimum transfer speed during video. In other words the transfer speed during video/burst should never be lower than the one denoted by the class, whereas advertising on the boxes and packaging typically show either the maximum or average transfer speed of the card.


When shopping for a card the speed class can make all the difference between your video being smooth and crisp or choppy due to skipped frames. If you use burst shooting a higher speed card can allow you to shoot for longer without having to pause and wait for a buffer to empty. As the market is always expanding and adding new sizes you can also reference the data available at the SD Card Association’s website: for up to date information on what options are available.


What symbols do you find most confusing when shopping for electronics?