Modern smartphones are filled with content at an alarming rate: high-resolution photos, 4K videos and heavy games take up gigabytes of internal memory in a matter of days. When the built-in storage becomes full, the device starts to work slower, and notifications about lack of space become more and more annoying. At this moment, users remember the memory card slot, which is found in many models, and think about expanding the storage.
However, when you come to a store or open an online store catalog, you can be faced with a real chaos of abbreviations. SDHC, SDXC, Class 10, UHS-I, A1, A2 - it is easy for an uninitiated person to get confused in these designations. Wrong choice format can lead to the card simply not being detected by the system or operating unstable, causing failures when recording video or installing applications. To avoid unnecessary expenses and disappointments, you need to understand the technical nuances.
In this article we will analyze in detail what what format of the memory card your Android smartphone really needs, how to read the label and what to look for when buying. Understanding these characteristics will help you choose a medium that will unleash the potential of your device to 100%, ensuring fast operation and reliable data storage for many years.
Physical formats and compatibility with the phone
The first thing you need to decide is the physical size of the card. In the world of mobile devices, the standard microSDalmost reigns supreme. Full-size SD cards (about the size of a postage stamp) are not installed in modern smartphones due to their obvious dimensions. Therefore, if you are choosing a storage device for your phone, your choice is limited only by the microSD family.
It is important to understand that even within the microSD format there is an evolution of standards that determine the maximum amount of memory. Older phones may not see large capacity cards due to file system and controller limitations. SDHC (Secure Digital High Capacity) support volumes from 2 to 32 GB, while SDXC (Secure Digital eXtended Capacity) work with volumes from 64 GB to 2 TB and use the exFAT file system.
If you have a budget smartphone that is three or four years old, it may not support cards larger than 32 GB. At the same time, modern flagships easily “see” terabyte drives. Before purchasing, be sure to check the specifications of your device on the manufacturer's official website to find out the maximum supported capacity.
⚠️ Attention: Do not try to insert an SDXC card (64 GB or more) into a very old smartphone that officially only supports SDHC. The phone may not see the card at all or may require formatting it to an incompatible FAT32 file system, which will limit the amount of available space.
Speed classes and UHS labeling
Once you have decided on the physical size and maximum volume, it’s time to figure out the operating speed. This is a critical setting, especially if you plan to shoot video or transfer applications to the card. On the card body you can find many icons with numbers, and each of them carries specific information about the minimum write speed.
The most basic indicator is Class Speed, indicated by a number inside the letter C. Class 2, 4, 6 and 10 indicate the minimum write speed in megabytes per second (2, 4, 6 and 10 MB/s respectively). Today, the de facto standard is Class 10. It makes no sense to buy SIM class cards for a smartphone, since they will slow down even when simply copying photos.
For higher-speed operations there is marking UHS (Ultra High Speed). A U icon with a 1 or 3 inside represents a data bus. U1 guarantees a write speed of at least 10 MB/s, and U3 - at least 30 MB/s. If you shoot video in 4K, the presence of the U3 marking is a mandatory requirement, otherwise the recording will be interrupted or jerky.
- 🚀 Class 10 —the basic minimum for installation in a smartphone, suitable for photos and Full HD video.
- ⚡ UHS-I (U1/U3) —a modern standard that ensures fast interface operation and 4K recording.
- 🏎️ UHS-II —an ultra-high-speed standard with two rows of contacts, but most smartphones do not support this bus.
It is worth noting that the presence of UHS-II support in a phone is very rare. Therefore, there is no point in overpaying for such cards; the phone will still work with them at UHS-I speed. The optimal choice for most users will be a card marked U3 and V30.
Video Speed Class specification for shooting
We should also talk about the marking Video Speed Class, which is indicated by the letter V with a number. This standard was introduced specifically for owners of cameras and smartphones that shoot high-definition video. The number after V indicates the minimum guaranteed sequential writing speed, which is critical for streaming data recording without buffering.
For owners of Android smartphones, the most relevant classes are V30, V60 and V90. The V30 class provides speeds from 30 MB/s and is the “golden mean” for shooting in 4K at 30 or 60 frames per second. The higher classes V60 and V90 are focused on professional video shooting in 8K and are much more expensive, while in mobile photography their potential often remains unrealized.
If your goal is simply to store music, documents or contacts, there is no need to overpay for a high Video Speed Class. However, if blogging or mobile video shooting is your hobby, skimping on this option will result in lost frames and corrupted files. Always check your phone's camera specifications before choosing a card.
Before buying an expensive memory card, check in the camera settings whether your smartphone supports 4K video recording. If the maximum camera resolution is 1080p, a V10 or U1 class card will be enough for you.
Application Performance Class for installing apps
Many users want to transfer heavy games and applications to a memory card to free up internal space. For this task, the normal sequential write speed (which we discussed above) is not as important as the random read and write speed of small files. This is where the standard comes into the picture. Application Performance Class.
This class is designated by the letter A with a number: A1 or A2. Class A1 cards guarantee a minimum of 1500 read operations and 500 write operations per second (IOPS). Class A2 cards are significantly more productive: 4000 read operations and 2000 write operations. If you plan to install games directly onto the card, choosing A2 will make loading levels and running applications much smoother.
Without support for the Application Performance Class standard, launching applications from a memory card may be accompanied by long freezes and freezes. The internal memory of smartphones (UFS) works on different principles than memory cards, so even a fast card will be slower than the built-in storage, but class A2 brings their performance as close as possible.
| Performance class | Min. reading (IOPS) | Min. recording (IOPS) | What is it suitable for |
|---|---|---|---|
| A1 | 1500 | 500 | Light applications, photos, videos |
| A2 | 4000 | 2000 | Heavy games, multitasking |
| No class A | Not guaranteed | Not guaranteed | File storage only |
⚠️ Attention: For A2 class cards to work, support is required from the Android operating system (starting from the Oreo version) and the specific smartphone processor. If the device is old, the A2 card may not work faster than the regular A1.
Brand reliability and memory types
The memory card market is oversaturated with offers, and among them there are many fakes or low-quality products. Using noname brands is a lottery in which you risk losing all your data in one moment. Memory cards have a limited resource for rewriting cells, and cheap models often use rejected memory chips, which fail faster.
Well-known manufacturers, such as SanDisk, Samsung, Kingston and Lexargive a guarantee on their products and use high-quality controllers. They also offer specialized series, for example SanDisk High Endurance or Samsung Pro Endurance, which are designed for devices with constant loop recording, such as DVRs or surveillance cameras, but are also great for active smartphones.
When purchasing, pay attention to the packaging and holograms. Counterfeit cards often have volume that is “drawn” in software but is not physically present. When recording data beyond the actual volume, the old information is simply overwritten, leading to irreversible damage to the files. Buy electronics only from trusted stores.
How to check the authenticity of a memory card?
Download the free h3testw or F3X utility to your computer. Insert the card through the card reader and run the writing and verification test. The app will fill all available space with data and then try to read it. If the card is fake, the utility will show errors and the real physical volume.
File system and formatting in Android
After installing a new card in your smartphone, the system will offer to configure it. Here an important choice arises: use the card as portable storage or as internal memory. This choice affects the file system and data availability. In portable storage mode, the card is formatted in exFAT or FAT32 and can be read on any other device.
Adoptable Storage mode encrypts the card and merges it with the system partition. In this case, the card is formatted in a specific format that is understandable only to that specific phone. It will not be possible to remove and read such a card on a computer without complex manipulations, but this allows you to install applications and system data on it.
The file system exFAT is preferable for cards larger than 32 GB, since it removes the limit on the size of one file of 4 GB, which is the old FAT32 system. If you shoot long videos in high quality, FAT32 simply will not allow you to save the file, interrupting the recording. Android will automatically select the desired system when formatting, but it is useful to know about this.
☑️ Check before purchasing a card
The “internal memory” mode speeds up the smartphone, but binds the card to the device forever. It should be used only if the internal memory is critically low and the card speed is high (A2).
Frequently asked questions about choosing memory cards
Can I use a memory card from a camera in a phone?
Physically, a full-size SD card will not fit into the microSD slot without a special adapter, which usually not included with camera cards. Additionally, camera cards are often optimized for sequential recording and may not be A1/A2 rated, which will make apps run slow on your phone. It is better to buy a specialized card for mobile devices.
Why does the phone write that the card is damaged immediately after insertion?
This could mean several things: the card is formatted in the NTFS file system, which Android cannot read without superuser rights; the card has physical contact damage; or the phone does not support the capacity of this card (for example, they inserted 512 GB into an old phone). Try formatting the card through the phone settings menu (Settings → Storage → SD card → Format), after saving the data on your PC.
Does the speed of the card affect the quality of photo shooting?
On The quality of the image itself (resolution, color rendition) is not affected by the speed of the card, the camera matrix is responsible for this. However, the speed affects the speed of saving a series of pictures (burst mode) and the time that the phone will be “busy” after pressing the shutter button. A slow card will force you to wait for the buffer to clear before taking the next frame.
How to transfer apps to a memory card?
In modern versions of Android, this feature is often hidden or only available for certain applications. Go to Settings → Applications, select the desired app, press Storage and, if the button is active, select Edit → SD card. If there is no button, the application developer has prohibited the transfer, or your card is not formatted as internal memory.