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SD Card Terminology: Size, Speed, Capacity

The chances are that you have come across a Secure Digital (SD) card before. If you own a mobile phone, digital camera or tablet computer then it is very likely that an SD card is the storage device of choice. More than 400 brands make use of them, but it can be difficult to understand the difference of one SD card to another. Is it compatible with your phone? Why do they come in different sizes? This article will help you crack open all the terminology and hopefully become more au fait with SD cards.

It’s worth knowing that something exists called the SD Association. This was founded in 2000 by Panasonic, SanDisk, Nintendo and Toshiba. Their aim is to promote the SD format and develop universal standards to ensure compatibility. There are now hundreds of general members of the association.

SD cards come in three different sizes (from largest to smallest): standard, mini and micro. Standard sizes are usually for things like laptops and printers; mini is often found in digital cameras; micro in tablets and smartphones. Usually the device will come with an SD card, so you can just take it out and read the label to see what size it is. If not, read the documentation and see what’s required – it may sound obvious, but only one size card will fit each device, unless it has multiple slots.

The next thing to take in to account is the speed of the SD card. This is measured by how quickly the information is read and written to and from the card. There are set speed standards that SD cards must adhere to depending on what their function is. For example, if it is to record HD video then it must be between Class 4 and 6 (a minimum speed of 4 MB/sec and 6 MB/sec respectively). As such, the higher the Class then the faster the card will perform. Again, refer to your device’s documentation to see what the minimum Class your SD card must be.

Finally, you need to be aware of the capacity of an SD card. There are three different types of card, each with their own capacity limits. An SDSC has a limit of 2 GB, SDHC is up to 32 GB and SDXC is 32 GB to 2 TB. When buying an SD card you should always get one that is going to be compatible with your device. For example, you could go out and buy a 1 TB SD card thinking you’ll be able to take loads of photos, only to then find it isn’t compatible with your camera. Your device will list its compatibility, so make sure you are getting a card that is within its limits.

Whenever in doubt, refer to the manual to see what type of SD card you should be buying. It’s not actually all as confusing as it might sound, as long as you understand that there are different types of cards that suit different needs.


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