This week, the SD Association announced the SD Specification 5.1 that will introduce a new classification system for SD cards designed to help customers understand the performance of their SD cards while using them to run apps. The first class is known as A1.
App Performance Class 1 is defined to require SD cards to provide the sustained sequential performance of 10 MB/s, and a performance of 1500 random read input/output operations per second (IOPS), as well as 500 random write IOPS. Anyway, various SD cards carrying the UHS Speed Class 1 already have to hit 10 MB/s, so this sequential performance mandated by A1 isn’t that demanding.
Since SD cards have developed from a pure file storage format to a kind of flash memory, which we often use to run apps, it has become necessary to include that additional regulation of IOPS performance.
With the launch of Android 6.0 Marshmallow, using SD cards as the primary storage in mobile devices has become very common. Especially, cards offering solid sequential performance without having random read/write capability are suitable for this kind of use. With the new App Performance ratings, it will be easier for you to know what kind of performance you may get.