What is an SD card?
An SD or Secure Digital card is a universal external storage card that is the dominant storage medium (size/method) for nearly all electronics. It was introduced in 1999 and fought against similar types of cards, but ultimately won.
What is a microSD card?
A microSD card is a super tiny version of an SD card. It’s literally fingernail-sized.
How do I know which size to buy?
It’s pretty easy… how big is the slot you’re gonna put it in? If it’s the size of your fingernail, then you need microSD. If it’s 32mm x 24mm (1.2in x 0.9in) in size, then you need an SD card (or a microSD card with an SD adapter).
Ubiquity
Many kinds of electronics can use SD or microSD cards these days. The Nintendo Switch, most Android cellphones & tablets, cameras (DSLR & mirrorless), and so much more.
Different Capacities
As of January 2021, there are 4 types of SD capacity technology. All these mean is the storage (not memory) capacity.
| SD | Up to 2 GB | Secure Digital |
| SDHC | > 2 GB – 32 GB | ” ” High Capacity |
| SDXC | > 32 GB – 2 TB | ” ” eXtended Capacity |
| SDUC | > 2 TB – 128 TB | ” ” Ultra Capacity |
Your device will need to know how to utilize the card you’re giving it. There are a lot of technical details here… the easiest way to know if your device will accept the card is to look at the manual or manufacturer’s website. Chances are just about any card will work in just about any device, but if your card doesn’t work, it may be that your device knows how to use SDXC and smaller, but can’t understand how to use an SDUC card.
Different Speeds
As of January 2021, we’ve got multiple different kinds of speeds. I’m going to borrow a chart from Wikipedia here to make it easy:
The Class cards are the old ones… if you have cheap electronics stores that have bunches of SD cards sitting in bins for like $6 each, they’re very likely Class cards… meaning slower speed. The card can’t physically take too much data in/out at any given time. The UHS (Ultra High Speed) are modern.
Imagine you’ve filled up your bath tub and you want all that water to drain in 3 seconds. It’s not going to happen, right? This is because you’ve got a small drain that it’ll all go down.
Now imagine you’ve got a camera that takes a burst of photos like 10 photos x 10 MB each = 100 MB in the matter of 2 seconds. If you’ve got a Class 2 (or a C2) card which can write (record) 2 MB/s. Assuming perfect conditions, you’re going to have to wait 50 seconds for that data to drain from the camera’s buffer (it’s actually RAM just like a computer) and get saved onto the card. Realistically, you’re probably going to wait closer to 90 or 120 seconds. If you keep taking photos, the buffer will fill up faster than it can drain and you will get an error and can’t take more photos until you let it drain.
Imagine that same scenario, but you’ve got a UHS 3 (U3) card. That can write data at upward of 30 MB/s. You’ll drain that 100 MB buffer in 3.3 seconds in perfect conditions, realistically closer to 5-8 seconds. In this scenario, you can shoot 50+ photos and then start having to slow down to let the buffer drain.
Which Should I Buy?
For my camera: Personally, I’ve been shooting for nearly 10 years. I’ve tested a lot of what’s available and I personally trust Samsung’s EVO Select line (it’s an Amazon exclusive, it’s exactly the same as the Samsung EVO plus cards). As I write this, their 64 GB U3 cards are $25, but I pay attention to pricing and buy 5 or so when they hit $15 or so. For help with watching prices on Amazon, read my article on CamelCamelCamel.com.
I have at least ten of these U3 64 GB cards around that I use exclusively for shooting.
For my phone/tablets/misc electronics: I still get Samsung’s EVO Select line, but I get the U1 speed because the price is much less and I go with larger for better capacity. You’re going to spend at least 50% less for that difference in speed (U3 vs U1) and it’s fine because the phone (or whatever) doesn’t need to save data that fast.