Chapter in this post:
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.
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:
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 with 120 frames per second, a V30 or U3 classification of the SD card is the basic requirement so that it can save around 30 megabytes of video material per second without failures (frame drops) produce.
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.
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 class||Minimum for random reading||Minimum for random writing||Minimum writing speed|
|Class 1 / A1||1500 IOPS||500 IOPS||10 MB / s|
|Class 2 / A2||4000 IOPS||2000 IOPS||10 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.
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.
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:
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Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.
The page contains affiliate links / images: Amazon.de