So, there are three aspects to a memory card. First is the capacity. In general, a 32 gigabyte memory card will record 4,000 JPEG images or 750 RAW images or three hours of HD video or maybe (and this depends greatly on several factors) 90 minutes of 4K video. Then you have to contend with build quality. Yes, there are differences here. I have never understood people who buy great cameras and then cheap out on memory (and for that matter, tripods). What good is a great camera if the memory card corrupts at a slight breeze?
The third factor is speed. There are two aspects to speed. And no, this is not a commonly known and even less commonly advertised fact. Let’s say you were going to start producing memory cards. By the way, don’t, it’s a totally saturated market. But for purposes of conversation, you did. All the industry requires you to advertise is the top speed your memory card reaches in a lab test. So this might be ninety megabytes a second, which we write as 90mb/s. But what if I also make memory cards (see what I mean? saturated market) and I also hit 90mb/s. But yours start processing at 25 mb/s and mine start at 45 mb/s and mine hit their top speed faster. Well, I have a better product right? Yes. But at the moment our labeling looks the same.
Today there are 25mb/s cards and they say “class 10” on them. Faster cards will say U1 and their top speed is between 45 and 90 mb/s. But they have no guaranteed beginning speed or rev up time. That’s why U3 exists. And no, U2 doesn’t exist, outside of the concert circuit. U3 means there is a floor to the memory card. This is usually 40 mb/s. So they start faster and rev up faster. Also, they can have faster top speeds.
A third piece of writing on the card will say a simple roman numeral I or II. This stands for UHS-I or UHS-II, which is a second layout of flash memory on the card. They actually do look different on the back of the card. A UHS-I card can hit 99 mb/s at a U3 speed. This is very good. But a UHS-II card can hit 285 mb/s. That’s stupid speed, which I love. But a few caveats first.
For a camera to utilize the UHS-II cards, it has to have the hardware to read the extra flash memory. If your camera lacks this extra hardware you can still buy a UHS-II card, but you aren’t actually utilizing it. Sorry. Also, if your camera’s video records in XAVC quality, you must have a 64 gigabyte card to shoot at your best quality. That said, all major 4K video manufacturers ask you to have a U3 card. So what should you have? I prioritize speed over capacity, personally, and have three U3 32 gigabyte cards and one U3 64 gigabyte card, which is for video.
Just thought I'd point that out.