SD cards, or secure digital cards, are a type of memory card used in various electronic devices such as digital cameras, smartphones, tablets, and more. SD cards come in different speed classes which indicate the minimum guaranteed sustained write speed.
What do the speed classes on SD cards mean?
The speed class rating on SD cards refers to its minimum guaranteed continuous writing speed. Higher speed classes can support faster read/write speeds and are better for recording high-resolution videos or transferring large files quickly. There are several main speed classes for SD cards:
- Class 2 – Minimum write speed of 2MB/s
- Class 4 – Minimum write speed of 4MB/s
- Class 6 – Minimum write speed of 6MB/s
- Class 10 – Minimum write speed of 10MB/s
- UHS Speed Class 1 (U1) – Minimum write speed of 10MB/s
- UHS Speed Class 3 (U3) – Minimum write speed of 30MB/s
- Video Speed Class V6, V10, V30, V60, V90 – Minimum sequential write speeds of 6MB/s, 10MB/s, 30MB/s, 60MB/s and 90MB/s respectively for video recording
The regular speed classes (2, 4, 6, 10) denote the minimum sustained write speed in MB/s. UHS refers to Ultra High Speed and guarantees even faster minimum speeds for high performance needs. Video Speed Classes designate minimum speeds for different video recording resolutions and frame rates.
Do higher speed class cards have any other advantages?
In addition to supporting faster write/read speeds, higher speed SD cards have a few other potential advantages:
- Better performance – higher data transfer speeds means less time waiting for files to copy or apps/games to load.
- Shoot high resolution photos/videos – higher resolution media requires fast write speeds to quickly save large file sizes.
- Faster buffer clearing – the camera’s data buffer clears faster so you can take more consecutive shots.
- Reduced risk of data bottlenecks – high speed cards can help prevent bottlenecks when recording or transferring data.
What are the different types of SD cards?
There are several physical sizes and capacities of SD cards:
- SD – original SD card design, available from 8MB to 2GB.
- SDHC (High Capacity) – offer 4GB to 32GB storage.
- SDXC (Extended Capacity) – provide 64GB to 2TB storage.
- SDIOC – input/output cards used in some cameras.
- miniSD – smaller version of SD cards.
- microSD – even smaller design widely used in mobile devices.
The SDHC and SDXC designs allow for higher maximum capacities on a single card. All types use the same interface and are backwards compatible with SD host devices. miniSD and microSD cards require an adapter to work in regular SD slots.
Sizes of SD Cards
| SD Card Type | Dimensions |
|---|---|
| SD | 32 mm x 24 mm x 2.1 mm |
| miniSD | 21.5 mm x 20 mm x 1.4 mm |
| microSD | 15 mm x 11 mm x 1 mm |
Are there limitations of speed classes?
There are a few limitations to consider around SD card speed classes:
- Minimum sustained speeds – Classes only guarantee a minimum sustained write speed, but not peak speeds.
- Real-world variability – Actual speeds may be lower than rated depending on the device and conditions.
- Read vs write – Class ratings only reflect write speeds. Read speeds are often significantly higher.
- Format affects speed – Cards formatted with FAT32 tend to have slower speeds than exFAT format.
- Counterfeits – Fake cards may have false speed labels that don’t reflect actual performance.
- Conditions affect speed – Extreme temperatures, file sizes, device compatibility and other factors impact real-world speeds.
While classes indicate minimum performance levels, a card’s true speeds can vary substantially based on many technical and environmental factors. Speed should be one of several considerations when selecting an SD card along with capacity, brand, price, reliability ratings and intended use case.
How are SD card speeds measured and tested?
SD card speeds are tested and measured in a few key ways:
- Standardized tests – The SD Association uses standardized test conditions to assign speed classes for guaranteed minimum write performance levels.
- Synthetic benchmarks – Programs like CrystalDiskMark test sequential and random read/write speeds in a simulated usage environment.
- Real-world testing – Reviewers test cards in actual use cases like transferring files, shooting video and loading games to gauge performance.
- Lab equipment – Hardware like digitizers and oscilloscopes directly measure the electrical performance of an SD card’s interface and components.
Combining synthetic benchmarks with real-world testing provides consumers a more accurate view of a card’s speed capabilities and consistency across different workloads. Standardized classification tests ensure cards meet their advertised minimum speeds. Lab testing provides detailed electrical insights at the component level.
SD Card Speed Test Results
| SD Card | Tested Write Speed | Tested Read Speed |
|---|---|---|
| SanDisk Ultra 80MB/s | 83 MB/s | 98 MB/s |
| Samsung EVO Plus 100MB/s | 92 MB/s | 107 MB/s |
| Lexar Professional 2000x 150MB/s | 135 MB/s | 205 MB/s |
What are the best uses for each speed class?
Different SD card speed classes are suited for different uses:
- Class 2 – Basic phones, low res cameras
- Class 4/6 – Basic point and shoot cameras
- Class 10 – Mainstream/beginner cameras, Full HD video
- U1 – Advanced point and shoot, DSLR HD video
- U3 – High bitrate 4K video, burst mode photography
- V6/V10 – 1080p and 1440p video at moderate frame rates
- V30/V60/V90 – 4K video at higher frame rates and bitrates
For basic mobile and digital photography needs, Class 10 and U1 cards offer a good balance of speed and value. High bitrate 4K video and advanced cameras and camcorders will benefit most from UHS-3, V30, and V60/V90 rated cards. Matching the SD card performance to your recording needs helps maximize device compatibility and avoid issues.
What are the major SD card manufacturers?
Some of the major brands manufacturing SD cards include:
- SanDisk – Pioneer in flash memory cards and market leader in SD cards. Offers a broad range of capacities and speeds.
- Samsung – Major electronics manufacturer that produces a full SD card lineup including EVO and PRO lines.
- Kingston – Leading independent memory manufacturer with Canvas, Professional and other SD card series.
- Lexar – Brand focused on high performance cards for photography and video professionals.
- Sony – Media giant that makes its own branded lineup of fast SD cards.
- PNY – Offers a wide range of affordably priced SD cards for general consumer use.
Other manufacturers like Transcend, Silicon Power, Patriot and Integral also produce SD cards. SanDisk and Samsung control the majority of the market in terms of units shipped worldwide. Lexar targets high-end professional use while PNY focuses more on value-oriented consumer SD cards.
Are there any compatibility issues to be aware of?
Most SD cards will work in compatible devices, but there are some compatibility considerations to keep in mind:
- Physical size – miniSD and microSD cards require adapters for standard SD slots.
- Capacity limits – Older devices may have limits on maximum card capacity.
- Speed interoperability – Using too slow card in fast device can hamper performance.
- Brand and model – Rarely, specific devices may have issues with certain card models.
- Counterfeits – Fakes and knockoffs may not work properly or can cause data loss.
- Format – SDXC cards need to be formatted exFAT for full capacity support.
Following manufacturer guidelines on card capacity and speed recommendations can help avoid issues. The SD Association specifics certification standards for interchangeability and interoperability that most branded cards adhere to when made and tested properly.
How can you identify fake or counterfeit SD cards?
There are a few ways to spot counterfeit or fake SD cards:
- Check manufacturer packaging – Fake cards often sold in plain silver cases.
- Inspect card exterior – Blurred logos, misspellings and irregularities may indicate a fake.
- Run software validator – Programs like H2testw can analyze full card capacity and catch fakes.
- Benchmark speeds – Counterfeits often fail to deliver advertised speeds.
- Research seller reputation – Buying from untrusted sites increases risk of fakes.
- Verify serial numbers – Manufacturers can confirm legitimacy of serials.
- Low prices – Extremely cheap cards compared to MSRP frequently indicate fakes.
Performing a full card read/write test, cross-checking serials with the manufacturer, researching sellers and inspecting packaging are some of the best ways to avoid counterfeit cards. Paying more for cards from reputable local or online retailers can significantly reduce the risks.
What are the key specs to look for when buying an SD card?
Main factors to consider when selecting an SD card:
- Capacity – Amount of storage you need for your intended use and devices.
- Speed rating – Faster cards improve performance but increase price.
- Card type – Size needs to physically fit your devices’ slots.
- Brand – Stick with major brands for reliability and warranty support.
- Price – Balance price against capacity, speeds and brand reputation.
- Endurance – Card life span or total bytes written rating.
- Usage – Tailor card specs towards your specific needs like 4K video or burst shooting.
Narrowing your card choice by identifying the most important performance and compatibility needs helps ensure you select the right SD card for your devices and budget.
Conclusion
SD cards offer a standardized way to add substantial removable storage capacity to consumer electronics devices. Their speed class ratings represent minimum sustained write speeds but real-world performance can vary based on numerous technical factors. Higher speed ratings allow support for advanced functionality like high bitrate 4K video recording and fast burst image capture. Major manufacturers like SanDisk, Samsung, Lexar and Sony offer a wide selection of SD cards targeted towards different use cases. Carefully matching the card capabilities to your device specs and requirements helps ensure optimal performance and compatibility.