If you’re someone who loves tech gadgets, you likely have a bunch of SD cards and microSD cards laying around. Memory cards can be found in a wide range of products from cell phones, drones, digital cameras, camcorders, and the list goes on. We all have lots of memory cards, but have you ever really stopped to look and understand what all the cryptic information on memory cards mean?

SD cards and microSD cards come in an incredibly wide range of sizes, speeds, and ratings. Do you know the difference between SD, SDHC, and SDXC? What is a UHS Speed Class? All of these ratings are governed and regulated by the SD Association. If you?re like most people, you probably based your purchasing decision on price and name brand. We?re here today to help you break down those bits of information and what they mean.

SD stands for Secure Digital. SDHC stands for Secure Digital High Capacity and SDXC stands for Secure Digital eXtended Capacity. The main differences between these labels comes in the way of maximum storage space. SD card capacity is up to 2GB, SDHC are more than 2GB and up to 32GB, and finally SDXC are 32GB up to a whopping 2TB. MicroSD cards follow the same concept as SD cards, with the main difference being in speed and capacity due to their smaller size.

Speaking of total capacity, the more storage space the card holds, the more data you can store on it. For example if you have a 4GB card, you can fit about 550 21 megapixel jpeg images or 30 minutes of 1080p video. Whereas with a 64GB card, you?d be able to fit 8,800 21 megapixel jpeg images and seven hours and thirty minutes of 1080p footage.

Maximum Read Speed is a measurement of how fast the information can be read from the card. Typically shown as a number followed by MB/s which indicates how fast data can be read from the card, for example 150MB/s. You may also see a different rating, such as 1000x. This number followed by the ?x? is the same information expressed a different way. Funny enough, the ?x? rating is a multiple of how much faster the read speed is compared to a CD-ROM drive speed of 150KB/s. To help put it in more modern terms, a rating of 633x is equal to 95Mb/s read speed.

Speed class ratings refer to the minimum sustained writing performance. SD cards and microSD cards have two levels of Speed Class. The standard Speed Class ranges from 2 to 10. These ratings are often indicated on the card with a number inside of a letter ?C?. Speed Class 2 has a minimum write speed of 2MB/s whereas Speed Class 10 has a minimum write speed of 10MB/s. You will also see another rating, UHS (Ultra High Speed) Class. These UHS Class ratings are displayed with a number inside of a letter ?U? and can be referred to as U1 or U3. UHS Class 1 and Speed Class 10 actually have the same minimum sustained write speed, but you?ll see later on in this article why UHS Class 1 will actually outperform Speed Class 10 in many cases. UHS Class 3 has a minimum write speed of 30MB/s.

The Speed Class of and SD card or microSD card is really important if you are recording in 4K video or shooting a lot of RAW images with your camera. The faster writing speeds ensures that you are able to capture all the footage accurately and without error. If you are shooting 4K, you definitely want a speed class of UHS-3. If you?re only doing 1080p then you will probably be fine with a UHS-1 or Speed Class 10 Rating.

Another UHS speed rating is the UHS BUS Speed. These speeds are often indicated on UHS class cards with a Roman numeral I or II. UHS-I and UHS-II are only found on SD and microSD cards that are UHS Speed Class 1 or 3. Generally speaking, the increased BUS Speeds on your memory cards is going to translate into higher data transfer rates giving you better overall read and write performance.

In the end, choosing the right memory card for the job is going to make a huge impact on your performance. When deciding which card to need, take these steps:

  • First know if you need a traditional SD card versus the smaller microSD card
  • Then decide what capacity you need
  • Then decide on what speed ratings you need for optimal performance

For example, if you?re buying a SD card for a traditional point-and-shoot type camera, then you would be fine with a Speed Class 10 card with anywhere from 4GB and up. However if you?re shooting 4K video at 30 frames a second, you will definitely want at minimum a UHS Class 3 or U3 card. There?s nothing worse than missing a shot or having unusable footage because your memory card can?t keep up with the needed speeds.