You might have seen new A1 and A2 speed ratings on some of the new SD and microSD cards. So what are they referring to, and should you take any notice of them?
The Short Answer:
For Cameras: You can safely ignore the A rating. Focus on V-ratings (V30, V60, V90) instead.
For Phones, Tablets, Steam Deck & Switch: The A rating is critical. It determines how fast apps and games load.
And in that case, an A2 rating is designed for higher performance than an A1 card.
Basically, the A speed rating measures the kind of short-burst and fragmented reading and writing that apps and gaming devices use. The older U or V ratings measure a different type of speed where large amounts of data are written sequentially in a data stream (as in video).
Related: not sure what the V30/V60/V90 and U3 symbols on a card actually mean? See my guide to SD card speed classes.
A1 vs A2 SD card ratings explained
SD and microSD cards have had several different speed rating categories. You see them in those small symbols and numbers on the cards and their packaging.
First, there was the speed class, which went from Class 2 to Class 10.
Then there was the UHS Speed Class, where the cards fall into either U1 or U3.
More recently, there’s a newer system, the Video Speed Class, that uses categories like V30, V60, and V90.
All of those are categories where the card is rated to meet or exceed a minimum threshold for sustained sequential write speed. Basically, that means they can keep up with a certain amount of data being recorded to them constantly. The obvious case where that comes into play is when recording high-definition (and ultra-high-definition (UHD)) video. The higher the quality and bitrate that the camera wants to record at, the faster the card needs to be to keep up with the stream of data coming at it. That’s why using a card that’s too slow in a 4K or 5K camera like a GoPro causes lockups and recording to stop–the card simply can’t keep up. One thing worth noting is that the actual speed you see in practical use is also very much dependent on the device you’re using it in, such as a camera or smartphone or another mobile device. In practice, the slowest link in the chain will determine the maximum speeds you get. So just because you have a very fast memory card doesn’t necessarily mean that you’ll see faster performance in practice.
So far, recording media like video, photos, and audio have been the primary market that SD and microSD cards have been aimed at. So the speed rating systems have reflected that emphasis on recording high-resolution video.
But more and more, memory cards are being used to extend the memory of devices that run apps. Devices like smartphones and mobile gaming consoles like the Nintendo Switch and Steam Deck, for example. The apps that run on these devices interact with memory space differently. Rather than a stream of sequential data, they want to write a lot of small chunks of data wherever there’s space available. That’s known as random read/write (compared to sequential read/write that’s important for video).
As you can clearly see in the speed test results I’ve posted, a card that is fast for sequential reading and writing isn’t necessarily fast for random reading and writing. So just because a card might be able to record very high bitrate 4K or even 8K video doesn’t necessarily mean that it’s going to be a good fit for the different kinds of use that applications might need.
As a result, the SD Association has come out with a new rating system specifically to categorize suitability for SD and microSD cards in application-heavy uses. It’s known as the Application Performance Class Specification, and it’s written in the form of A1 or A2. The idea behind it is that if you’re using the SD or microSD card to run applications on your mobile device, you can have confidence that a given card will be suitable before you buy it and will hopefully reduce the frustration of users buying cards blind that simply aren’t well-suited to running apps.
So far, there are only two designated classes: A1 and A2. The SD Association will add more as they’re needed. The thresholds to meet these categories are:
A1
To display the A1 symbol, a card must meet or exceed these thresholds:
- Random Read: 1500 IOPS
- Random Write: 500 IOPS
- Sustained Sequential Write: 10 megabytes per second
A2
For the A2 category, it should be able to do at least:
- Random Read: 4000 IOPS
- Random Write: 2000 IOPS
- Sustained Sequential Write: 10 megabytes per second
Note: To get the full speed benefits of A2 (Command Queuing and Cache), your device must specifically support the A2 standard. If used in an older device, an A2 card might not be faster than an A1 card.
IOPS
The “IOPS” here stands for input-output access per second. It’s a different measure than we’re used to with memory cards, where the speed has typically been measured in megabits per second or megabytes per second in keeping with how video bitrate is measured and visual media recorded to the card. But the IOPS measure is more meaningful for measuring the kinds of operations that apps do.
You’ll also notice that the specification includes a minimum requirement for sequential write. The 10MB/s threshold corresponds to a Class 10 video speed rating, which is too slow for many of today’s cameras that record 4K, 5K, or 8K video.
Is the application performance class specification relevant to digital cameras?
No. Cameras are sequential write devices. They simply do not benefit from the high random read/write IOPS performance that A-rated cards provide.
When shooting and saving photos and videos, the type of speed that matters with digital cameras is the minimum sequential write speed, because a large, constant stream of data (eg. HD video, 4K video, or even 8K video) needs to be written to the memory card at high speed.
It’s also worth pointing out that the A rating is a parallel rating system to the V and U systems. What I mean by that is that it doesn’t replace them, and it’s entirely possible — even likely — to have a card that carries both the A1 rating and a V30 rating or an A2 as well as a V90 rating. They’re referring to two different things.
