SD cards are small removable storage cards commonly used in digital cameras, cell phones, tablets, drones, dash cams, handheld gaming systems, and more. They allow you to capture photos, videos, music, documents, and other files. SD cards come in different storage capacities and speed classes indicating their performance level.
The newer and faster A1 and A2 speed classes were introduced in 2017 and 2018, respectively, for SD cards to better support the advanced media capabilities of smartphones and other mobile devices. They go beyond the previous UHS speed classes to provide higher levels of random read/write speeds and sustained sequential performance critical for 4K video capture, burst mode photography, gaming, and app performance. But which is better – A1 or A2?
Background on SD Cards
SD cards were first introduced in 1999 as a joint effort between SanDisk, Panasonic, and Toshiba as an improvement over MultiMediaCards (MMC). The SD format was based on the MMC format but included Digital Rights Management (DRM) and Write-Protect features [1]. The SD card provided greater capacity and speed compared to previous formats like CompactFlash.
There are several types of SD cards that have emerged over the years, including [1]:
- SD – The original SD card design with dimensions of 32 x 24 x 2.1 mm
- MiniSD – A smaller version with dimensions of 21.5 x 20 x 1.4 mm
- MicroSD – An even smaller design with dimensions of 15 x 11 x 1 mm
SD cards are commonly used in digital cameras, camcorders, mobile phones, tablets, gaming consoles, drones, and other electronics. They provide removable storage for photos, videos, music, documents, apps, and other data [2].
SD Card Speed Classes
SD card speed classes were created by the SD Association to provide a standardized way to indicate the minimum performance capabilities of SD cards in various use cases. The speed class rating on an SD card refers to its minimum guaranteed sustained write speed, which is measured in megabytes per second (MB/s).
There are several speed classes that can appear on SD cards:
- Class 2 – Minimum write speed of 2 MB/s
- Class 4 – Minimum write speed of 4 MB/s
- Class 6 – Minimum write speed of 6 MB/s
- Class 10 – Minimum write speed of 10 MB/s
Cards with faster speed class ratings are better suited for recording high resolution videos, high bitrate audio, burst photography, and other demanding applications. Most basic SD cards today are Class 10, indicating a minimum sustained write speed of 10 MB/s.
Beyond the standard speed classes, there are also UHS speed classes designed for ultra high-speed SD cards using the UHS-I and UHS-II interfaces. UHS-I cards have bus interface speeds up to 104 MB/s and UHS-II cards can reach bus speeds up to 312 MB/s. Common UHS speed ratings include UHS Speed Class 1 (U1) and UHS Speed Class 3 (U3).
Introducing A1 and A2
The A1 and A2 speed classes for SD cards were introduced in 2016 by the SD Association. They designate cards that are optimized for app performance, with minimum random read and write speeds.
The A1 specification requires a minimum sustained random read speed of 1500 IOPS (input/output operations per second) and a minimum sustained random write speed of 500 IOPS. The A2 specification builds on A1 with higher minimum requirements – 4000 IOPS random read and 2000 IOPS random write.
So in summary, A2 cards have significantly faster sustained random read and write speeds compared to A1, making them better optimized for running apps and games. The A1 spec is more of an entry-level app performance rating, while A2 represents more advanced performance 1.
A1 Speed Class
The A1 speed class was introduced in 2016 for microSD cards used in mobile devices. According to the SD Association, A1 cards must meet the following minimum performance requirements:
- Sequential read speed: At least 10MB/s
- Sequential write speed: At least 500KB/s
- Random read speed: At least 1,500 IOPS with 4KB blocks
- Random write speed: At least 500 IOPS with 4KB blocks
The random read and write speeds are particularly important for A1 cards, as they determine performance in running apps and other random access tasks. The A1 class targets cards used in smartphones and tablets for the following types of applications:
- Launching apps quickly
- Loading cached data from storage
- Saving game data
- Recording 4K video
In summary, A1 microSD cards are optimized for random read/write speeds to provide a responsive experience in mobile devices for frequently used apps, games, and tasks involving storage access.
A2 Speed Class
The A2 speed class was introduced in SD 6.0 specifications to indicate enhanced performance capabilities for advanced applications. To qualify as A2, a card must meet the following minimum requirements as per the SD Association:
Sequential Write Speed: 10MB/s
Random Write Speed: 4000 IOPS
Random Read Speed: 4000 IOPS
The higher sequential and random read/write speeds make A2 cards better suited for advanced apps, especially those that use the card as extended storage. Examples include:
- Professional photography and videography apps with burst mode shooting and 4K video recording. As per SD Association, A2 cards enable capture of large numbers of high-resolution images and extended lengths of 4K video.
- Gaming apps that read and write frequently like 3D games, multiplayer online battle arenas, etc. The faster speeds ensure lower load times and smoother gameplay.
In summary, A2 cards provide enhanced performance for advanced apps that require sustained sequential and random writes at high speeds.
Comparing Performance
When looking at benchmarks, A2 cards consistently outperform A1 cards, but the real-world differences are less noticeable for many everyday uses.
In typical benchmarks like CrystalDiskMark, A2 cards show significantly higher 4K random read/write speeds compared to A1. For example, the SanDisk Extreme A2 microSD gets up to 1900/1000 IOPS read/write compared to 1500/500 IOPS for their Extreme A1 card 1. These results translate to better performance in intensive applications like recording or playing back high bitrate 4K video.
However, for typical usage in apps, games, and lower resolution video, A1 cards are often sufficient. The small random read/write speed differences between A1 and A2 won’t be noticeable in lighter workloads. An A1 card can still reliably run apps and games designed for the A1/A2 spec. The performance gains only manifest in very I/O intensive workloads.
Ultimately, while A2 benchmarks faster, A1 cards provide adequate performance for most use cases. But for professional/industrial applications requiring sustained high speed I/O, A2 is recommended.
Pricing Differences
Overall, A2 SD cards tend to be more expensive than A1 cards when comparing prices per gigabyte. According to Amazon, a 128GB A1 micro SD card averages around $20, while a comparable 128GB A2 card averages around $25-30.
For example, the SanDisk Extreme Pro 128GB A2 micro SD card sells for $29.99, working out to around 24 cents per gigabyte. In comparison, the SanDisk Ultra 128GB A1 micro SD card goes for $18.99, or about 15 cents per gigabyte.
The price difference is largely attributed to the faster speeds and app performance that A2 cards offer over A1. However, for standard uses like full HD video recording, an A1 card is often sufficient while being more budget-friendly.
Use Cases: When to Choose A1 vs A2
When choosing between an A1 or A2 SD card, it often comes down to budget vs performance. A1 cards tend to be more affordable, while A2 cards offer faster random read/write speeds that benefit certain use cases.
For basic needs like full HD video recording, an A1 card is typically sufficient. The fast sequential write speeds of A1 meet the minimum requirements for recording high-resolution video at Full HD or 4K. However, the random performance of A1 cards can sometimes cause lags or frame drops during continuous burst shooting with cameras and drones. This is where A2 cards have the advantage.
The boosted random read/write capabilities of A2 cards make them better suited for devices that need to save files in rapid succession. This includes high-end mirrorless and DSLR cameras capturing rapid burst shots or RAW photos, as well as drones recording high bitrate video. The faster random performance reduces latency and prevents occasional lagging or frame drops.
For budget-focused users who don’t need peak performance, an A1 card still offers decent speeds at a lower price point. But those wanting the best performance for intense applications should choose A2 for seamless stable recording and capture.
Recommendations
When choosing between A1 and A2 SD cards, it depends on your specific use case. Here are some recommendations for the best A1 and A2 cards for different needs:
For Nintendo Switch or mobile gaming: SanDisk MicroSDXC Ultra 400GB. This A2 card has excellent 4K random read speeds perfect for gaming.
For DSLR/4K video recording: Samsung PRO Endurance 128GB. This A2 card has great sustained write speeds for recording high-res video.
For photo storage: SanDisk Extreme 128GB. The A1 rating provides good speeds for transferring photos.
For budget pick: PNY Elite 512GB. Decent A1 speeds at an affordable price.
Overall, A2 cards edge out A1 in terms of performance, but come at a price premium. For most use cases, A1 provides sufficient speeds at a lower cost. However, for intensive tasks like gaming or 4K video, spring for an A2 card.