hesela.devSD Application Performance Class
SD Application Performance Class specifies minimum random-access and sustained sequential-write performance under defined card and host conditions.
A1 specifies at least 1,500 random-read IOPS and 500 random-write IOPS; A2 specifies 4,000 and 2,000 respectively. Both include a 10 MB/s sustained sequential-write requirement under the specified test conditions [1].
Physical Layer Simplified Specification 7.10, section 4.16.1.2, requires cache use for A2. It permits SD Express and SDUC cards without command-queue support; when supported, the queue must be used. Other A2 card types require command queuing. With queue and cache disabled, an A2 card must support A1 conditions [2].
These classes do not specify data retention or power-loss protection. A host must flush an enabled card cache before power-down; acceptance into the cache is not completion of that flush [3].