Google released Android 6.0 Marshmallow a little over a year ago, which introduced several new features. One of these is support for "adoptable storage," that is the ability to tell your smartphone or tablet that the MicroSD card you have installed is to be considered as internal memory. This feature means that Android devices can have much more memory available for installing applications as well as the more typical media storage. There are a few reasons why Google may have introduced adoptable storage, but the main one is believed to be in support of the Android One smartphones, which typically had very limited internal memory, quickly filled up by installing only a few applications. The technology means that a device with a quoted 4GB or 8GB of internal storage (usually reduced by around 3GB by the time the operating system has been installed) can use a reasonably large capacity MicroSD card of say 32 GB and install applications onto here instead.
However, there are a few potential issues with using adoptable storage. One is that the user may decide to remove the MicroSD card from the device, which will cause applications to fail and might result in data loss. Android contains several warnings about this. Another is the security implication of using the MicroSD card, but these are encrypted to only work with the one device. A third potential problem is the reliability of the MicroSD card, as a cheap, unreliable card could cause application or even operating system crashes and failures. And finally the last potential issue is that of performance: internal memory chips are on the whole much quicker than relying on external memory. Some of the performance bottleneck is associated with the memory card adapter but much of it is associated with the memory card itself. Fortunately, the SD Association have put together a new class of MicroSD card designed with running applications in mind: SD Specification 5.1 includes the new "Application Performance Class," which has been designed to let consumers know that the card they're buying is suitable for use for Adoptable Storage purposes. Furthermore, these cards are being marked with a new symbol, which you can see below the article together with a YouTube video clip explaining things below.
As for the performance necessary to use the MicroSD cards for Adoptable Storage, the new class of cards must offer a Random Read Input-Output access Per Second, or IOPS, of 1,500. The Write IOPS must be at least 500 and the cards must be capable of a Sustained Sequential performance of 10MB/s. There will be two grades of App Performance with the higher grade, SDA, designed for higher performance cards. The new branding is good news: until now, the only way to figure out if your particular card is fast enough to properly support Adoptable Storage is either to search the Internet to see if somebody else has tried using it, or to install it and try the option yourself.