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Learn how to buy SD or microSD card correctly for your purpose

Article last updated: 08/04/2019

Have you ever taken an SD card in your hand and seen a lot of numbers and letters on it without having a clue what they mean? In this article we explain what each one means and give you tips on how to choose the card according to its use.

Quick Guide:

If you are currently in a store or very close to buying the card and need to quickly understand how to evaluate it, we have made this image below for your guidance. We use MicroSD cards as reference in the images, but all information is also valid for larger SD models.

Why so many numbers and letters?

Technologies change constantly, every year there is some improvement in software or hardware, so storage media such as SD need to keep up.

SD Assosciation has created classes and nomenclatures so we can identify how each card works just by looking (despite the wide variety of information), they are spelled on the card and are very visible, let's understand what they mean?


These are the currently available card templates, each has a format, a storage memory limit, and are available in version micro SD. Currently the most common models are SDHC and SDXCThis is because SD supports a maximum of 2GB of storage.

SD, Secure High Capacity (SDHC) and Secure Extended Capacity (SDXC)

These markings do not define which card has the fastest file transfer speed, they only define storage limit and format type. Before you buy a card for your smartphone, camera, drone, or other device, look at what standards it supports.

SD Standard – supports up to 2GB of storage memory using system FAT 12 or FAT 16 News

D to buy a smartphone with the value of the accessory

SDHC Standard – Supports 2GB to 32GB storage memory and uses formatting FAT32

SDXC Standard – supports 32 to 2TB of storage memory using exFAT formatting

The pattern appears graphed as in the image above. In the example above, on the left is microSDXC and right is microSDHC.

When formatting the card, it is recommended to use this software from SD Association which guarantees the ideal settings according to the model. Formatting a card anyway, regardless of the file system, is sure to have performance issues or malfunctions. For example, you decide to put a 64GB SDXC card in a device that only supports up to 32GB (SDHC), this will not work!

Another detail, and perhaps you have already noticed, is that although most smartphones currently support up to 2TB of storage, you will often see a micro SD with this sale specification. This is because these devices are not currently manufactured. SanDisk's model with the most storage memory today was released in 2019. It has 1TB and is, of course, in the SDXC category.

Even if microSDs are not yet available with 2TB, manufacturers fit the technology and sell their future-proof handsets. Although most people change their smarpthones in a few years, some even from year to year.


This class defines the minimum sequential recording speed supported by the card. If your card is class 10, for example, it is guaranteed by the manufacturer that it offers at least 10 MB / s of sequential recording. It appears in a C with the class number inside, just like the image above. If you want to shoot in full HD, it is recommended that you use a card at least class 6.

Supported classes and speeds:

Class 2 – Supports up to 2 MB / s of sequential recording

Class 4 – Supports up to 4 MB / s of sequential recording

Class 6 – Supports up to 6 MB / s of sequential recording

Class 10 – Supports up to 10 MB / s of sequential recording

UHS and speed modes 1, 2 and 3

The SD Association explains on this page that Default Speed, listed in the table below, was the first speed mode created and supported up to 12.5 MB / s. Next was created High Speed ​​mode thinking about the emergence of digital cameras. Later other models were established with the intention of speeding up reading and writing, such as: UHS-I, UHS-II and UHS-III.

These standards define how the card communicates with the device and even have physical changes from one to another, but this physical difference only occurs from the UHS I to UHS II model as in the image below. UHS II and UHS III have the same form. These additional pins allow for faster read and write speeds.

There are currently no products on the market that appear with UHS III. We contacted the SD Association and they replied that there is not yet a date for the cards to start arriving with the apparent UHS III.

When it hits the market, UHS III will appear on the cards as in the image opposite.

Remember that this table is designated by the SD Association and this does not mean that all companies follow it to the letter, so even with this information, it is important to know as much as you can about a card before you buy it.

U1, and U3

To rate the speed UHS The SD Association created the classes U1 and U3. After the creation of speed classes 2, 4, 6, 10, an exclusive technology class UHS was presented, U1 and U3.

The SD card, that older model that supports a maximum of 2 GB of storage, is not represented by speeds U1 and U3. Only UHS I, UHS II, and UHS III appear in this class.

U1 guarantees a minimum write speed of 10MB / s, while the U3 offers at least 30MB / s. Below is an example of how they appear on the card.

How to buy the best microSD for smartphone?

Your choice will depend on the use you want to have on your smartphone. Below we talk about the use of Apps on the smartphone.

Application use

With the launch of Android Marshmallow 6.0 in 2015, it became possible to install applications on microSD in case there is little space available on internal storage. But for these apps to work well you need to choose the card that has the ideal ideas.

So you can run apps fast and smoothly on your smartphone, just buy one micro SD with high MB / s transfer. Smartphone applications need to read many small files at once instead of a few large files from time to time. In this case, MB / s are not that important, which really matters how much IOPS supported by the card.

IOPS stands for: Input and Output Operations per Second

The higher the number of IOPS, the more files can be transferred at one time and this is what matters most when running apps on smartphones, as apps often require reading many small files.

Fine, but how do I know when buying? Will I have to read some manual or try my luck? The SD Association has created a certificate to help you consumers identify when microSD offers the minimum necessary to perform well with applications on your device. Currently the cards indicated for use in smartphones come with the certificate TO 1 or A2 spelled.

Note that between the two classes released the amount of MB / s the same, which shows exactly what I commented above, what really matters in the performance of microSD in smartphones the number of IOPS. Amid other certificates, A1 and A2 appear as in the image below.

In the video below you can see the difference between application speed when using a microSD with A1 and another without this standard. At the beginning of the video, at 19 seconds, he explains that A1 is a new format that allows reading and writing files randomly unlike sequentially.

How to buy the right card to shoot smoothly?

Buying a card that is not fast enough to record video on your device, be it a drone, a smartphone or a professional camera, cause audio and picture delays on the recorded video or the device will display an error message. The latter situation has been more common lately in drones.


Device the fastest UHS-I flash card in the world

But then how do you know which card to use when shooting? You basically need to know what quality you are going to record at and what the transfer speed in MB / s is for this quality you choose. If you have a drone that shoots in 4k, you don't want to buy a 10 MB / s transfer card, for example.

The SD Association has created a card speed class to facilitate proper selection. This class is written on the card and is divided into V6, V10, V30, V60, V90. Each indicates an average write speed in MB / s. Below you see microSDXC UHS U3 V30 cards with A1 technology.

In this case the V30 indicates that this card is capable of transferring files at a sequential minimum speed of 30MB / s. It is suitable for recordings in Fullhd and even 4k. However, not all cards come with this marking, as it is somewhat new and there are still many older products released prior to it circulating on the market. So it is often necessary to be guided by the other classes. In the table below you can see the equivalent speeds between classes and the supported qualities. If you look for a card V30 and don't find a card U3 serve well as the table shows.

This table by the SD Association summarizes very well what you need to know when buying your movie card. If you only want FullHD, a class 10, U1 or V10 card will ensure that the video is recorded smoothly.

It is important to note that in the table, the SD Association warns, in its upper right corner, that the speed required for recording varies according to the conditions determined on the device. Taking this into consideration, it is more appropriate if you want to shoot in Full hd, buy at least one card V10 and risk one V6, for example. If you want 4k, choose one that is at least U3 or V30, try to film 8k with V30, certainly not perfect or not even recognized by the device.

Unfortunately having to understand all this complicated letter soup for those who simply want to buy a card and go recording. Anyway, we need to ask 3 questions: what format does my device support (SDXC or SDHC), what am I going to do with it (shoot, use apps), how fast I want to record (to know which class is best). This makes it easier to organize this mess. We hope we helped, any questions, can send question in the comments.

SD Express Cards

The SD Association has introduced a new standard that uses NVMe and PCIe technologies for reading and storing information on memory cards. The name given to the cards was SD Express and allows transfer speeds of up to 985MB / s. In addition to specifications that guarantee much more speed, reaching almost 10 times more than the current, also has backwards compatibility with various devices on the market.

According to the SD Association, this also enables more storage memory, rising from 2TB (SDXC) to 128TB (SDUC). They act as the popular SSDs, Solid States Drivers, which are trending and should be set as the storage standard soon.

NM Cards and the future of memory cards

Mobile devices are the industry's main motivation for continuing to evolve storage technologies with faster speed, lower power consumption and also a smaller size. In smartphones this is very evident, since getting a little more space can allow a larger battery or a thinner body.

To try to approach this solution, from now on we should expect technologies to take up a smaller footprint and offer a greater number of advantages. Huawei, the Chinese smartphone company, recently introduced its two tops of the line, the Mate 20 and the Mate 20 Pro. In them, a new technology was introduced, the NM Card, or Nano Memory Card. According to the company, this new memory card 45% smaller than the microSDs and can offer the minimum of 256GB storage with transfer speeds up to 90MB / s.

The most interesting thing about this Huawei technology is the possibility of the user choosing if he uses the space of his SIM chip for a phone chip or for storage with an NM Card. Other companies have already suggested replacing microSDs, Huawei was not the first. THE Sony tried to popularize the Memory Stick, and Samsung the UFS card, but none of them were very successful. As the Nano Card has only been adopted by Huawi so far, it remains to be seen to see if it is adopted by other manufacturers.

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