If you've attempted to buy an SD or microSD card recently, you probably found out that there are many different kinds of cards with numerous different features. Depending on what device we intend to use the SD card on, we need to choose the appropriate UHS class, the Speed Class, the App Performance Class, and so on. Will it be V30 and above? How many GBs will we need? SDXC or SDHC?
We realize that for those who do not know what all these mean and want a card for their cell phone, buying an SD card can be a headache.
Sure, we could list the best SD and microSD cards in the market, and suggest specific features for each use. However, we think it is worth mentioning what those ratings mean and what purpose they serve.
If you are just looking for an SD card or a microSD card and you don’t want to know what all the fuss is about, you can just skip to the end of this guide.
Table of Contents
- How does an SD card work?
- What does Secure Digital mean?
- Solving the mystery...
- Bus Speed
- What about Speed Class?
- App Performance Class
- SD and microSD buying guide
- Did we help you pick an SD card?
How does an SD card work?
Secure Digital cards - yes, this is what SD stands for - are flash memory cards, and we use them as external storage on our modern devices.
SD cards differ from other flash memories since we can write over them thousands of times without damaging them. At the same time, they do not need any power to keep their data, as RAMs do. They do not even have moving parts like HDDs.
In other words, in a way, they are like tiny SSD drives, albeit with much lower performance.
The above features make them ideal for use on smartphones, digital cameras, and other devices that need portability, ample storage space, and endurance.
As with SSDs, the data on an SD card is stored in a series of electronic parts called NAND chips.
These circuits allow the data to be recorded and stored in the memory card. And since there are no moving parts, the data can be transferred at high speeds to and from the card, far exceeding the speeds of CD / DVDs or HDDs.
What does Secure Digital mean?
Before moving on, we'll say that SD cards conform to the standards developed and continue to be established by the Secure Digital Association.
The association was created by Panasonic, SanDisk, and Toshiba in January 2000 to develop and promote storage standards for flash memories.
In fact, the association used SanDisk’s technology as the basis for the new standards. We shouldn’t forget that SanDisk is the world leader when it comes to flash memory products.
The SD Association's headquarters are located in San Ramon, California, but it is not an organization or company that produces and promotes SD cards on the market. On the contrary, it is precisely what its name says: an association.
More than one thousand manufacturers are joining the association to contribute to the development of SD card technology and to create new standards.
In fact, if you look at any memory card, you will see the logo of the union.
If you've ever wondered why all SD cards have the same logo, now you know the reason.
Solving the mystery...
As already mentioned, the features on an SD card can seem extremely confusing, and may leave us scratching our heads. Indeed, we can not understand how something so small can be so complicated.
Below we will attempt to solve this puzzle, hoping we won't do more harm than good.
Thus, let's look at the categories one by one.
The physical size is the easiest factor to understand when talking about buying an SD card. Things are relatively simple, since each device only accepts a certain size.
Available sizes are shown in the image below.
SD or Full SD
This is the most common size on a memory card. These cards have nine pins at the back and are 32 x 24mm in size. Their thickness is at 2.1mm.
On their left side, we will find a switch that is used for write protection. We'll usually find these cards in digital cameras, camcorders, and other recorders.
The "mini" version of an SD card is called miniSD and is 20 x 21.5 mm in size, 1.4mm thick. It has 11 pins at the back, and it was the first attempt at downscaling the normal SD card.
Nowadays, it is very rare in devices, compared to the other two types.
Lastly, we have microSD cards. They are even smaller, at 15 x 11 mm, with a thickness of 1mm. They have eight pins at the back, and due to their small size, they are mainly used on smartphones.
Which one to choose?
Always choose the size that suits your device, which is pinpointed on the manual, or next to the device’s port.
We can also use special adapters to place micro and miniSD cards on Full SD ports.
So, if we already have an excellent microSD card, for example, and we want to place it in a camera that only accepts SD cards, maybe a simple adapter will suffice.
Our microSD might have already come with an adapter, as most manufacturers include it on the packaging.
Note that using the adapter will have no impact on the speed of the card. However, the ideal scenario is to use the specific size designed for each port.
Things are relatively simple in terms of capacity as well. In the market, we will find cards from 1GB up to several GBs. In fact, the larger SD cards to date are up to 512GB. The largest microSD card is a SanDisk, and it also amounts to 512GB.
However, we should pay close attention to cards that claim large capacities for a meager amount of money.
Apart from the fact that cards with such storage space sizes don’t exist yet, do you think it’s reasonable for an SD card to cost less than a 1TB HDD?
The miniSD cards, as we will see, do not reach such large capacities. Since they're practically a species that's near extinction in the market, their development has stopped.
So, we can simply choose the capacity of our SD card according to our needs, right?
No, the manufacturers didn’t want that to be so easy. Thus, they added extra letters and terminologies to SD cards, which are practically useless since they have to do with the capacity.
In other words, we have three card models in terms of capacity. From the oldest to the newest, they are the following:
If our card only has an SD logo on it, then its capacity is up to 2GB. Nowadays, this sign is almost extinct, since the 2GB capacity is not enough for even a 10-minute video on a modern smartphone.
This template uses a FAT 12 and 16 file system.
If the "SD" logo is accompanied by the letters "HC", then it means that the card capacity ranges from 4GB to 32GB. HC stands for "High Capacity".
As we mentioned above, this name is a useless advertising trick, since virtually every card shows exactly how many GBs it has.
However, SDHC cards use the FAT32 file system; this is why we can not write more than 4GB-files on these cards.
For example, if we have an SDHC card and record a video with a camcorder, once our video reaches 4GB, the camera will create a new video file even if we do not stop recording.
Respectively, "XC" stands for "Extended Capacity", which means even greater storage space. More specifically, SDXC cards start at 32GB, and they have the potential to go up to 2TB - once the manufacturers are able to build such cards.
This category includes only SD and microSD cards, as miniSDs do not come in such sizes.
In this template, the file system is exFAT, which means it doesn’t have the limitation of 4GB of the FAT format.
The largest file that can be stored in an exFAT file system is 16EB (Exabyte), equivalent to 16,000,000 TB. As you may have realized, chances are none of us will leave long enough to hold a card with such a storage capacity.
Which one to choose?
Although things are just about capacity, we need to check whether our device supports the standard of the card we choose. Some older devices do not accept more than 2GB. In other words, they do not support SDXC or SDHC.
The device or the manual usually displays one of the three logos below, depending on the template it supports.
Let us also mention that in logos, the capacity standards are combined with sizes. That is, if the device supports a microSD card, it will display a “microSDHC” or “microSDXC” logo.
The choice, therefore, is easy to make. If our device supports it, we select SDXC without a second thought. If it does not, or if we do not want such a big card, the SDHC is the way to go.
Now, if we have such an old device that it does not accept any of the above, maybe it's time to replace it.
In any case, devices always report the maximum limit in GB. Thus, we shouldn’t buy a memory card above this limit, because it won’t work.
The term UHS was created in 2010, and it is a brand marketing that refers to the type of bus that the memory card has, and thus the maximum speeds it can reach.
Below are the types of bus that exist so far, along with the maximum speeds they support.
Default Speed and High Speed
Default Speed is quite deprecated and marks bus 1.01.
The High Speed is also old, and it designates the maximum speeds for the simple SD cards we mentioned above. It also refers to bus version 1.10.
From version 3.01 onwards, the terminology changed to UHS, and the maximum card speeds increased respectively.
The table below provides some much-needed clarifications.
As we can see, the UHS is marked with I, II, or III next to the SDXC or SDHC logo. Simple SD cards do not support UHS, and there is no logo for Default Speed and High-Speed classes.
Which one to choose?
It is important to mention that the UHS-II, created in 2011, has a different layout on the cards than the UHS-I. The additional row of pins increases the available bandwidth to 150-300MB/s.
However, to take full advantage of a UHS-II memory card, our device must have the necessary pin connectors to read it correctly.
Until today, there are no UHS-II cell phones on the market, while users report low speeds by placing UHS-II cards on UHS-I slots. UHS-III cards, however, will be compatible with UHS-II ports when they are released on the market.
Also, all UHS types are backward-compatible with the previous generation. If we already have a UHS-I card but our device supports UHS-II, we will have no problem using it.
Again, we should consult our device’s manual to see the supported format.
If we have a card that does not support UHS, it means it has an older type of bus and therefore supports much slower speeds.
Usually, such cards will come at a meager price, despite the enormous capacities they may have.
Do not fall into the trap, though. We recommend at least UHS-I cards for every modern device unless our phone - for instance - is so old that it does not support it.
What about Speed Class?
The speed of a card does not play a special role when we just store files or take pictures with a smartphone. However, it's extremely important when we shoot video, especially if it's a high-resolution video.
Obviously, if our card cannot write data as quickly as our camera shoots, the resulting file will be unwatchable, and it won’t be the camera’s fault.
But, wait a second. Didn’t we just cover the bus speed on the section above?
Well, bus speed is the maximum speed that SD cards can achieve, depending on the type of bus they have.
But what about the minimum speeds? This is what the Speed Class is.
We should mention that we are talking about writing, not reading speeds, which is what we are most interested in.
The SD Association has created three classification categories that deal with how fast an SD card is at writing data. Each group has a bunch of subcategories. In fact, one card may fall into two or all three categories at the same time.
It seems that they weren't quite happy with the mess one category could create.
These categories are similar to the 80 Plus certifications in power supplies, but imagine it being much worse and confusing.
What can we say, the SD Association is not that famous for its effective marketing strategies.
The first certification is called "Speed Class," and refers to the minimum recording speed.
Speed Class is marked with a number inside a "C" shape on the card, and depending on the number, the card falls into four subcategories: Class 2, 4, 6, and 10.
Fortunately, these numbers are not random, but they designate the minimum writing speed in MB/s in each category. For example, a card that falls under Speed Class 6 guarantees a minimum write speed of 6MB/s.
Ultra High-Speed Class
The UHS Speed Class is another "measurement unit" of the recording speed for SD cards and refers more specifically to the minimum recording speed for videos. What's the difference; None, really.
Okay, it marks the transition to UHS bus from the High-Speed bus, but as far as speed is concerned, it makes no difference.
In short, the previous Speed Class terminology could be continued by merely increasing speeds.
So far there are two subcategories: UHS Speed Class 1 and 3. We will find them as U1 and U3.
Their logo is U-shaped, and the corresponding number is shown inside. The U1 supports a minimum write rate of 10MB/s, while U3 is 30MB/s.
In short, if the card has U1 or U3 certification, it means it has a UHS bus - something we knew because it has a separate UHS mark on it - and now it has the minimum speeds of 10MB/s and 30MB/s respectively.
Video Speed Class
Video Speed Class was created to distinguish cards that can support high resolution recording (4K or 8K).
This category also certifies support for the next generation flash memory, such as 3D NAND.
Video Speed Class, or just V Class, is denoted by the letter V and the minimum write speed in MB/s.
There are five available subcategories: V6, V10, V30, V60, and V90.
On some SD cards, manufacturers decide to add their own maximum speeds based on measurements they made on their products.
So, coupled with all of the symbols we have seen so far, on some cards we will also find a maximum speed. Those represent reading speeds, most of the time.
What on earth should I choose?
Good question. The following table summarizes all the above.
In general, the biggest certification is the one that matters. In other words, on cards that support V90, we will also find U3 and C10, which are practically useless to us.
No matter what device we want to use, nowadays we should always aim for at least U3 or V30 SD cards unless our hardware states otherwise.
If we have such a limited budget, we can drop down to U1 or V10, but only for playback or storage uses, rather than video recordings. Of course, the price gap is not that big, so it is not even worth considering.
In general, we should stay away from SD cards rated lower than U1, V10, and Class 10. These cards are a waste of money.
Professional photographers and videographers who record their material at 8K may find it to be worth investing in V60 and V90 cards. For the, even for 4K hardware, V30 cards are more than enough.
App Performance Class
The SD Association never misses an opportunity to create new logos and classes. Let’s hope they will run out of available space on the front of the card before they run out of letters.
The App Performance Class is a relatively new marketing terminology, which indicates that a card is good enough to install and run mobile apps smoothly.
Generally speaking, for video recording, we are interested in the continuous writing of a large file. This speed is known as sequential write speed.
On the contrary, devices such as smartphones and portable consoles interact with the memory space differently. Instead of a large file, they write and read multiple small files, which are stored in several places.
This type of speed is referred to as random read and random write speed. App Performance Class, therefore, certifies this type of speed.
There are two levels available: App Performance Class 1 and 2, or just A1 and A2.
The predicted speeds are shown in the table above.
Which one to choose?
Since this certification is new, there are not so many A1 models on the market, while A2 does not exist yet.
So, the problem of choosing between the two is pretty straightforward. The real question is, is it generally worth investing in an A1 memory card against a card that does not have this certification?
The answer is yes if we are going to use the memory card on smartphones or consoles to install apps and games on it.
Even the fastest memory card we have, regarding sequential write, does not guarantee that it will be equally fast at random read and write speeds.
On the other hand, if we want to use the card just for file storage or on cameras, the A1 certification is useless.
SD and microSD buying guide
Based on what we have described so far, in theory, we can pick an SD card depending on our needs.
Below we recommend some of the best cards in the market for each category. We have included models for the most common sizes in each class. There are countless cards from various manufacturers, so it's practically impossible to name them all.
If you are looking for something more specific, and the list didn’t cover your needs, feel free to leave a comment below, and we will suggest the card that suits your device.
UHS-II for maximum performance
If we want the best one to go, we need to put our hand deep into our pocket. UHS-II cards are the most expensive on the market, and for a good reason.
We will not get a UHS-II card for a smartphone, because they simply do not support them. It makes sense to look at such cards only for recording 4K videos, and only if you shoot at 60fps and above.
And since you are going the UHS-II route, you probably aim for large capacities, usually more than 64GB.
Thus, we suggest:
- Amplim V60 U3 C10 32GB-256GBama
- SanDisk Extreme Pro U3 64GB
- Sony SF-G64 U3 C10 32GB-128GB
- microSD SanDisk Extreme Pro U3 64GB
- microSD Lexar Professional 1800X U3 C10 32GB-128GB
- microSD Lexar Professional 1000X U3 32GB-128GB
UHS-I A1 to install smartphone apps
If we are looking to purchase an SD card for smartphones, these are the categories we are interested in for maximum performance.
Obviously, we look at the microSD category, as this is the standard for smartphones today.
- SanDisk Extreme Pro V30 U3 C10 A1 32GB
- Amplim V30 U3 A1 64GB
- Amplim V30 U3 A1 128GB
- SanDisk Extreme V30 U3 A1 256GB
UHS-I U3 or V30 and above for general usage
In this category, we will find the most VFM cards in terms of dollars to GB ratio, but also in terms of speed.
These cards will cover us for use on smartphones, cameras, and generally in 90% of cases if we are not looking for something more specialized. Most of the cards below come in various capacities so that you can choose according to your needs.
UHS-I U1 or V10
As we warned earlier, we do not recommend buying SD cards under the U3 classification. They have significantly lower speeds, without much value when it comes to price.
However, for simple storage space, and only if there is an absolute need to save some money, you can choose from the list below. Again, you can choose the capacity of your preference for each model.
- Transcend U1 C10 16GB-128GB
- Samsung EVO U1 32GB-128GB
- PNY Elite Performance U1 C10 32GB-512GB
- SanDisk Ultra C10 8GB-64GB
SD and microSD cards under U1 / V10 / Class 10
We can not recommend buying SD cards with these specifications, because we can not imagine anyone using them today.
Did we help you pick an SD card?
Buying an SD card should be a much more straightforward procedure than it is. With all these marketing names, it is very easy to confuse even the most experienced user.
If we helped you clear the mess in your head about all the SD card classifications, don’t forget to leave a comment below.
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