What do the abbreviations A1 and A2 mean on SD cards?

The App Performance Class is irrelevant for use in photo or video cameras. However, if you want to use the microSD card in your smartphone to expand the internal memory, you should definitely buy an A2 card (Photo: Sir Apfelot).

If you look at the abbreviations that you find on an SD card or MicroSD card, you will notice that some models also contain the designations "A1" or "A2". A reader asked me a few days ago what these abbreviations are all about and what they are important for. Then it was time to take a closer look and read, because I - to be honest - I didn't know either.

The imprint "A2" is becoming more and more common on microSD cards. What it means is explained here! (Photo: Sir Apfelot)

The imprint "A2" is becoming more and more common on microSD cards. What it means is explained here! (Photo: Sir Apfelot)

Application Performance Class, UHS and VSC

In addition to the storage capacity itself - 16 GB, 32 GB, etc. - there are also other classifications of the microSD cards printed on their surface. This is common here UHS classwhich can be between U1 and U3, as well as the newer "Video Speed ​​Class", which is either V6, V10, V30, V60 or V90. An explanatory graphic can be found on sdcard.org:

In this overview you can see the different speed classes as well as the possible video resolution for which they are recommended (graphic: sdcard.org).

In this overview you can see the different speed classes as well as the possible video resolution for which they are recommended (graphic: sdcard.org).

Both classes provide information about the minimum write speed, which is important for video recordings, since the memory card has to write large amounts of data in a short time. For example, if you have a 4K camera that works at 120 frames per second, a V30 or U3 classification of the SD card is the basic requirement so that it can save approx. 30 megabytes per second of video material without failures (frame drops). generate.

microSD card as memory expansion for the smartphone

As an iPhone user, you don't have the option, but many Android smartphones allow you to expand the device's internal memory by inserting a microSD card.

Here, however, new challenges are placed on the storage medium, because while a memory card in a video or photo camera almost exclusively writes large files and hardly reads them, an SD card in a smartphone has to switch quickly between different files and between read and write mode can jump here. The operating system wants to save settings, access and create caches, start apps and open many small files. That means: many accesses in the shortest possible time.

The last SanDisk Extreme that I bought for my Insta360 One X was already classified as an A2 microSD card "by default" (Photo: Sir Apfelot).

The last SanDisk Extreme that I bought for my Insta360 One X was already classified as an A2 microSD card "by default" (Photo: Sir Apfelot).

So that a memory card does not slow down the operating system, it has to manage many read and write operations per second, and this is exactly where the SD card standard "Application Performance Class" comes into play. A fast SD card is of little use in the smartphone if it does not allow fast file access. For this reason, the app performance class (A1 and A2) defines a minimum value in this area.

The following table shows the specifications that an SD card must meet in order to meet the A1 or A2 standard.

App performance classMinimum for random readingMinimum for random writingMinimum writing speed
Class 1 / A11500 IOPS500 IOPS10 MB / s
Class 2 / A24000 IOPS2000 IOPS10 MB / s

Note: IOPS = input-output access per second.

The A1 standard is defined in the SD Physical 5.1 specification, while the A2 standard is defined in the SD Physical 6.0 specification.

A translated quote from the description of the A2 class:

The speed advantages that the A2 standard offers in practice arise primarily from functions such as "command queuing" and caching. Maintenance functions are also helpful during operation in order to enable efficient memory management.

You can see that much more emphasis is placed on fast access times than on higher read / write rates. This is also more important when using the memory cards in a smartphone.

Test conditions for the IOPS value

The values ​​for the number of accesses are abbreviated as "IOPS" in the table above, this abbreviation for "input-output access per second". In order to determine the value, read and write accesses with 4KB files are carried out in random order. More details can be found in this article the SD Association.

The App Performance Class is irrelevant for use in photo or video cameras. However, if you want to use the microSD card in your smartphone to expand the internal memory, you should definitely buy an A2 card (Photo: Sir Apfelot).

The App Performance Class is irrelevant for use in photo or video cameras. However, if you want to use the microSD card in your smartphone to expand the internal memory, you should definitely buy an A2 card (Photo: Sir Apfelot).

Using a microSD card without A1 standard in the smartphone?

Of course, you can use any microSD card in your smartphone to expand the memory. Even cards without the A1 or A2 standard are basically compatible, but there is no guarantee that they will achieve a certain speed or a certain amount of read / write processes per second.

In practice, however, it has been shown that SD cards without the A1 standard, for example, slow down the start of Android apps on smartphones by around 25%. The comparison to A2 SD cards should be even clearer.

So if you want to use a microSD card as a memory extension for your Samsung Galaxy or another smartphone, you should prefer SD cards with the A2 standard.

I have listed the current microSD card bestsellers from Amazon for you - of course only these with the A2 standard:

64,00 EURBestseller no. 1
SanDisk Extreme microSDXC UHS-I memory card 512 GB + adapter (for smartphones, action cameras and ...
98 Reviews
SanDisk Extreme microSDXC UHS-I memory card 512 GB + adapter (for smartphones, action cameras and ...
  • The SanDisk Extreme microSD memory card is ideal for all Android smartphones, tablets, action cams and...
  • A read speed of up to 190 MB / s and a write speed of up to 130 MB / s enables you to ...
  • The microSD memory card offers fast in-app performance and super-fast loading thanks to the A2 rating
159,99 EURBestseller no. 2
SanDisk 1 TB Extreme PRO microSDXC card + SD adapter + RescuePRO Deluxe, up to 200 MB/s, with A2...
  • The SanDisk Extreme PRO microSDXC is ideally suited for all Android smartphones and tablets, as well as drones or...
  • The microSD card ensures better app performance and faster loading thanks to the existing A2...
  • With a reading speed of 200 MB/s and a writing speed of 140 MB/s, you can transfer your data...
2,00 EURBestseller no. 3
Gigastone 4K Camera Pro 256GB MicroSDXC memory card and SD adapter, compatible with GoPro drone ...
  • [Speed]: Read and write speed up to 100/60 MB / s, V30 speed level, Ultra HD (UHD) ...
  • [App]: A2 grade offers faster app loading performance for smartphones and tablets.
  • [Storage]: Extends the internal storage space of the smartphone. Allows moving / downloading the apps ...
11,91 EURBestseller no. 4
SanDisk Extreme microSDXC UHS-I memory card 128 GB + adapter (for smartphones, action cameras and ...
  • The SanDisk Extreme microSD memory card is ideal for all Android smartphones, tablets, action cams and...
  • A read speed of up to 190 MB / s and a write speed of up to 90 MB / s enables you to ...
  • The microSD memory card offers fast in-app performance and super-fast loading thanks to the A2 rating
Bestseller no. 5
Lexar Micro SD card 256GB, microSDXC UHS-II MLC memory card Micro SD 1000X with SD adapter, up to...
  • HIGH-SPEED TRANSPORT: microSDXC card supports UHS-II interface, U3/V60 speed class. Up to 150MB/s...
  • Widespread application: The Lexar Micro SD card offers high compatibility for various types of ...
  • Designed for durability: The memory card is shockproof, waterproof, temperature-resistant,...
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The page contains affiliate links / images: Amazon.de

2 comments

  1. Thank you, Sir Apfelot, for this post! Informative, including an enlightening effect!

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