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The buyer’s guide to getting the right microSD card

Note: This article was first published on 20th February 2018.

Not all microSD cards are created equal

The microSD card is ubiquitous in the gadgets we use today. It’s rare for the average user to give it further thought – you buy one, and simply pop it into your device for more storage space. While that line of thought works, microSD cards can offer more to its users when they understand the full breadth and capabilities of the card better.

Sadly, not all microSD cards are created equal. Certain cards are better for loading apps for an Android smartphone, while others are better for portable gaming consoles, 4K video recording, photography, and other usage scenarios.

The minute differences in microSD card options are what prompted us to do a simple buying guide to help you better purchase the right type of card for your gadget and needs. Besides understanding the core specifications on your preferred card, we’ll also share some basic shopping tips in this guide.

It’s not just about the size

Storage size is one of the first considerations, but it shouldn’t be the only spec to care about because the rest of the symbols on your card indicates its overall performance.

Those symbols come from a standard created by a non-profit organization called SD Association. Founded in 2000 by SanDisk, Panasonic, and Toshiba, the SD Association attempts to simplify all the other specs that affect the performance of your SD and microSD cards. SD Association isn’t exactly the best at communicating these numbers to your average smartphone-touting auntie or uncle.

Image credit: The Straits Times.

The infographic by The Straits Times provides a visual way to understand what each symbol and its placement means. Below is a quick run-down on what your card is trying to tell you:


The storage size of your card in gigabytes (GB). This is pretty straightforward. As of writing, these cards can usually be found in 32GB, 64GB, 128GB, and 256GB. The theoretical maximum storage for SD and microSD cards is 2TB, but the largest known microSD capacity now sits at only 400GB.

Card type

This is only important if you’re using old gadgets from 2009 or earlier. The first generation’s called SD (Secure Digital), followed by SDHC (Secure Digital High Capacity), and the current generation is called SDXC (Secure Digital Extended Capacity). Each card type comes from a different technological age, so an old device with support up to SDHC may not be able to take in the new SDXC card. If your device can receive the latest card type, chances are, it can accept the older generations too.

Speed Class

The speed class of the card refers to its minimum sequential write speed, which is essential for video recording. SD Association continually updates its marketing tactics for sequential write speeds, which gets convoluted over time. Mostly, it has undergone three evolutions, namely:-

  • “Speed Class”, denoted by a number with a near-complete circle around it. It signifies the sequential write speed for the card. Speed Class 10, for instance, has a minimum write speed of 10MB/s.
  • “UHS Speed Class”, denoted by a number inside a U-shaped symbol. U1 represents a minimum of 10MB/s, while U3 indicates the card’s ability to write 30MB/s or higher sequentially. This particular speed class was introduced between 2010 to 2013.
  • “Video Speed Class” denoted by a stylized “V” followed by a number. “V30” means it has a minimum write speed of 30MB/s.

Currently, the highest available speed class is V90 (which means the card can sequentially write at 90MB/s or higher). If you are recording 4K video footage, SD Association recommends any card between 10MB/s to 60MB/s. That means that any card with Speed Class 10, U1, U3, V10, V30, or V60, is suitable for recording 4K footage.

Application Performance Class

This is a new standard created by SD Association in 2016, denoted by a stylized “A” next to a number. This performance class refers to the card’s minimum random read and random write speeds (measured in input/output operations per second – IOPS).

Currently, there are only A1 and A2 standards, and A1-capable cards have only recently entered consumer space. A1 has a minimum random write of 500 IOPS and minimum random read of 1,500 IOPS, while A2’s sits at 2,000 IOPS and 4,000 IOPS respectively.

Ideally, the higher-than-usual IOPS on these cards would allow smartphone users with Android 6.0 (and newer) to install apps using the Android Adopted Storage feature. Broadly speaking, users who have the habit of installing game apps onto the memory card will see reduced loading times, especially at the app’s startup. You can read much more about the new class here.

Take note that Android Adopted Storage encrypts the microSD card and treats it as part of the phone, so removing the microSD card would likely cause issues to the device and refuse to run – until you reformat the card and reset the phone. As such, consider this form of usage only if you don’t plan to remove the microSD card from the device.

Putting it all together

By applying what we’ve learned to The Straits Times’s infographic above, you can decode the symbols and understand what the card offers. The answer: it’s a 32GB microSD card that’s likely compatible with 2006 or newer devices, and it can record 4K videos at 30MB/s, with support for Android Adopted storage smartphones.

Here’s a table that captures how the SD card specifications have evolved over time:-

So, what microSD card should I get?

By now, it’s evident that the right microSD card for your device largely depends on the gadget you’re using.

A 4K action camera like the GoPro Hero6 can accept up to microSDXC cards, with Class 10 or U1 speeds, and a maximum capacity of 256GB. This particular SanDisk Ultra microSD card would seem like a good fit.

A person using an entry-level smartphone like a Xiaomi Redmi Note 4 would only have 32GB onboard storage, but the phone can accept microSD cards up to 128GB in capacity. The phone also comes with Android 6.0 OS, so it’s possible to use Android Adopted Storage. This means that a 128GB microSD card with A1 performance class would be ideal, so that the user can run as many apps as possible from the microSD, instead of using the limited internal storage space.

On the other hand, a user with a flagship smartphone like the Samsung Galaxy Note8 would be tempted to get a 256GB, A1-capable microSD for the device. However, the Note8’s internal storage uses UFS 2.0, which is still faster than loading apps from external storage. Perhaps a card with only Class 10 or U1 speeds would suffice for storing photos and videos since the phone already has an internal storage of 64GB for apps.

Armed with this information, we hope you’d be able to get a microSD card that’s best suited for your needs. If you have a favourite microSD card or brand, let us know in the comments!

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