The A2 symbol on SD cards refers to the speed class rating established by the SD Association for SD cards used in applications with sequential writes. The A2 rating indicates that the card can sustain minimum sequential write speeds of 10MB/s and meet a minimum random read IOPS of 4000 and write IOPS of 2000.
What do the different symbols on SD cards mean?
There are several different symbols that can appear on SD cards that indicate different speed classes and capabilities:
- C2 – Indicates the card can sustain minimum sequential write speed of 2MB/s
- C4 – Indicates the card can sustain minimum sequential write speed of 4MB/s
- C6 – Indicates the card can sustain minimum sequential write speed of 6MB/s
- C10 – Indicates the card can sustain minimum sequential write speed of 10MB/s
- U1 – Indicates the card can sustain minimum random read IOPS of 1500 and write IOPS of 500
- U3 – Indicates the card can sustain minimum random read IOPS of 4000 and write IOPS of 2000
- V6 – Indicates the card can sustain minimum sequential read speed of 6MB/s and sequential write speed of 6MB/s for video recording
- V10 – Indicates the card can sustain minimum sequential read speed of 10MB/s and sequential write speed of 10MB/s for video recording
- V30 – Indicates the card can sustain minimum sequential write speed of 30MB/s for video recording
- V60 – Indicates the card can sustain minimum sequential write speed of 60MB/s for video recording
- V90 – Indicates the card can sustain minimum sequential write speed of 90MB/s for video recording
The A2 rating combines both the U3 random IOPS rating and a minimum 10MB/s sequential write speed.
What types of applications is the A2 rating designed for?
The A2 rating is designed for applications that require both sustained sequential write performance and random read/write IOPS performance. Some examples include:
- Smartphones – Operating systems, apps, and photos/videos benefit from fast sequential writes and random IOPS.
- Tablets – Powering productivity apps, multi-tasking, games, and media consumption.
- Digital cameras – Fast shot-to-shot performance, rapid sequential writes for photos and video.
- 4K/8K Video recording – High resolution video requires fast sequential write speeds to avoid frame drops or lag.
- Gaming devices – Games with rich graphics, fast loads, and constant reads/writes for save games and updates.
- Drones – HD video recording while in flight demands sustained write performance.
- Dash cams and security cameras – Non-stop HD video recording under all conditions.
The A2 specification aims to provide high performance for both intensive multimedia workloads as well as general smartphone/tablet usage.
What are the minimum requirements for an A2 rated SD card?
To carry the A2 rating, SD cards must meet the following minimum performance thresholds:
- Sequential write speed of 10MB/s
- Random read IOPS of 4000
- Random write IOPS of 2000
These requirements are meant to ensure the card can handle sustained write-intensive workloads as well as random reads/writes for tasks like operating system and app usage.
How is the A2 rating different from other SD card speed classes?
Here is a comparison between the A2 rating and other common SD card speed classes:
| Rating | Sequential Write | Random Read IOPS | Random Write IOPS |
|---|---|---|---|
| C10 | 10 MB/s | Not specified | Not specified |
| U1 | Not specified | 1500 | 500 |
| U3 | Not specified | 4000 | 2000 |
| A2 | 10 MB/s | 4000 | 2000 |
The A2 builds on both the sequential performance of U1 and random IOPS ratings of U3 to deliver a combination meant for intensive smartphone/tablet workloads.
What kind of performance can you expect from an A2 card?
While actual performance can vary between cards, here are some general performance guidelines for A2 SD cards based on the rating criteria:
- Sequential writes up to ~30MB/s for 64GB cards or ~50MB/s for 128GB+ cards
- Sequential reads up to ~100MB/s
- 4K random reads up to 10,000-20,000 IOPS
- 4K random writes up to 5,000-10,000 IOPS
Higher capacity cards tend to enable faster performance simply due to having more NAND flash chips and parallelism. Factors like manufacturer, NAND type, controller, form factor, and testing methodology also impact speeds.
Should you choose an A1 or A2 card?
The A1 and A2 ratings both aim for cards designed for app performance:
- A1 focuses on random read IOPS, requiring 1500 IOPS minimum.
- A2 requires higher 4000 read IOPS and adds 2000 write IOPS minimum.
A2 is better suited for intensive workloads like 4K video recording, graphics-intensive games, multi-tasking, and burst shooting modes. A1 is sufficient for simpler apps, lower resolution photography/video, social media, and music.
What are the best A2 microSD cards?
Here are some top options for A2 microSD cards across different storage sizes:
| Card | Storage | Sequential Read | Sequential Write |
|---|---|---|---|
| SanDisk Extreme | 64GB | 160MB/s | 60MB/s |
| Samsung EVO Select | 128GB | 100MB/s | 90MB/s |
| Lexar Play | 256GB | 150MB/s | 87MB/s |
| PNY Elite-X | 512GB | 100MB/s | 90MB/s |
There are also A2 microSDXC cards available up to 1TB for maximum storage. Top brands like SanDisk, Samsung, Lexar, and PNY all offer solid performance, reliability, and warranty coverage.
Do all devices support A2 SD cards?
The A2 rating relies on the UHS-I interface and is backwards compatible with older hosts. However, the device must support UHS-I in order to take advantage of the extra speed capabilities of A2 cards. UHS-I was introduced in 2009 and is supported by most modern devices.
Older devices without UHS-I can still use A2 cards but will be limited to legacy speed modes. It’s a good idea to check your device’s tech specs or manual to confirm UHS-I support if you want to leverage the full performance.
How can you test the performance of your A2 card?
There are a few options for testing your A2 card to see if it lives up to its rated performance:
- Tools built into your OS – For example, BlackMagic on Macs or DiskMark in Windows.
- Cross-platform tools – Such as CrystalDiskMark or ATTO Disk Benchmark.
- IOmeter – For in-depth testing of IOPS performance.
- Real-world use – Try recording high bitrate video and see if it keeps up.
Test sequential and random read/write speeds using different block sizes. Compare against manufacturer specs or other cards to get a sense of expected performance.
How does the A2 rating compare to NVMe SSDs?
NVMe SSDs used in PC’s and laptops outperform A2 SD cards significantly:
- Sequential read – NVMe SSDs over 2500MB/s, A2 SD cards ~100MB/s
- Sequential write – NVMe SSDs up to 2500MB/s, A2 SD cards ~50MB/s
- Random read IOPS – NVMe SSDs up to 700K, A2 SD cards up to 20K
- Random write IOPS – NVMe SSDs over 150K, A2 SD cards up to 10K
However, A2 SD cards provide huge performance gains over hard disk drives and SATA SSDs. The small physical size and removable/portable nature of A2 SD cards make them very useful for smartphones, drones, cameras, and other devices.
Conclusion
The A2 rating indicates an SD card is designed to handle sustained write-intensive workloads while maintaining solid random read/write IOPS. It meets the demands of recording high-bitrate 4K/8K video, graphics-intensive gaming, burst-mode photography, and powerful productivity apps.
A2 builds on previous standards like U1 and U3 to deliver excellent performance for smartphones, tablets, cameras, gaming devices, and more. When shopping for a high-endurance SD card optimized for demanding multimedia workloads, the A2 marking signifies a great choice.
