ST Digital's microSD buying guide

A1 memory cards best fit for mobile devices

The new rating guarantees the SD card is consistently fast enough to run apps directly off it

The new A1 rating indicates that microSD memory cards have met the performance standards for running apps reliably in mobile devices.
The new A1 rating indicates that microSD memory cards have met the performance standards for running apps reliably in mobile devices. PHOTO: REUTERS

Those looking to buy a flash memory card to store apps, music and photos in their Android smartphones and tablets now have an easier time picking a suitable card.

Retailers such as Best Denki, Challenger, Harvey Norman and Newstead Technologies have started bringing in microSD memory cards with the new A1 rating, which indicates that the card has met the performance standards for running apps reliably in mobile devices.

The A1 rating (Application Performance Class 1) was introduced as part of the SD 5.1 specifications released last November by the SD Association industry group, which represents over 900 manufacturers.

Memory maker SanDisk subsequently showed off its first A1-compliant memory products at the CES trade show in January.

Unlike digital video cameras that write large chunks of data to their memory cards at a time, the apps in smartphones typically write small amounts of data to random locations in the device's internal storage or memory card.

Therefore, a memory card needs to offer good sequential read and write speeds to perform well in cameras, but random read and write speeds are more important for apps in mobile devices.

To achieve the A1 rating, a memory card must provide a random read performance of 1,500 IOPS, a random write IOPS of 500 and a sustained sequential performance of 10MB/s. IOPS (input/output operations per second) is widely used to measure storage performance.

  • How we tested


    The microSD cards were tested with a Transcend USB 3.0 card reader connected to our computer. The storage benchmark - CrystalDiskMark 5.2.1 - was used to measure the sequential read and write speeds, as well as the random read and write performance of these cards.


    The one thing that stood out were the random write IOPS numbers for the Samsung Evo Plus and the SanDisk Extreme.

    IOPS (Input/Output Per Second) tells us how fast a device is able to handle I/O requests, which affects storage performance.

    These two cards were the only ones in this test to exceed 500 IOPS, which is the minimum number mandated by the A1 class rating. In other words, these two cards will run applications smoothly when used in your smartphones. They both even cost around the same at $1.08 to $1.09 per gigabyte.

    All the microSD cards, except for the Strontium Nitro, managed to meet the minimum A1 class requirements for random read performance. In fact, the Nitro's sequential write numbers are dismal for its price.

    The Toshiba Exceria looks like a good deal - it posted solid numbers for its price ($0.68 per gigabyte) - especially when compared with the Samsung Evo ($0.66 per gigabyte).

    Sony's microSD card is significantly more expensive than its competitors, though the company does include a free utility to recover data from damaged cards.

    Vincent Chang

Mr Kevin Schader, director of communications at the SD Association, said: "Recent changes to the Android operating system (see Adoptable Storage sidebar on the right) allow users to directly run apps from and store apps onto their microSD memory card. We designed the A1 App Performance Class as an easier way for consumers to find the right card for smartphones and tablets."

He told The Straits Times that A2 class memory cards that offer even better performance are likely to arrive in stores within a year. Samples of these A2 cards were unveiled at recent trade shows like Computex.

Gartner analyst Manjunath Bhat said that the new standard "improves the performance of the card so apps can now run directly off the microSD card". But he also believes that the future of the memory format is uncertain: "Technologies such as Android Instant apps will supersede and pose an existential threat to the microSD card."

Android Instant apps let users run apps without having to first install them on their devices. Since May this year, all app developers can build Instant app versions of their software.

"Mobile-device manufacturers are trying to minimise the number of moving parts for better reliability. They are embedding even SIM cards (called e-SIMs) into non-removable slots. The microSD card will follow a trend similar to that of the good old floppy disk," he said.

The Straits Times Digital spoke to a handful of smartphone users about the A1-rated microSD cards. None of them were aware of the rating, but they were open to trying out such cards.

Asked if she would be interested in the new A1 memory card, Ms Siti Aishah, 26, said: "It depends on the performance - but, yes, definitely. I think a microSD is important for phone backup."

To find out if the A1 card lives up to its billing, we obtained an A1-compliant SanDisk Ultra 32GB microSD card and compared it with a bunch of microSD cards bought from local stores.

How to pick the right microSD card

Before buying a new microSD card, ask yourself which device it is going into. Is it for a smartphone, camera or laptop?

A microSD card that is quick at writing small amounts of data to random locations in its memory is more suitable for smartphones and tablets. Meanwhile, a camera recording a 4K video is writing to a contiguous segment of the microSD's memory, which means sequential, not random, write performance is more important.

The SD Association has helpfully created various class ratings - Application Performance and Video Speed classes - to help consumers pick the right card.

But these labels are not always printed on the card. Alternatively, you can look at the read and write speeds provided, though these numbers usually refer to the sequential read and write speeds.

Manufacturers also use descriptors such as 4K video recording, as well as "action camera" and "tablets and smartphones" to indicate their suitability for these devices.

Most microSD cards come with 10-year or limited lifetime warranties, though a few offer shorter warranties.

Beware of fake microSD cards that have less storage than advertised. They are usually slower too, which may affect your device's performance. Buy your card from a reputable retailer instead of auction sites like eBay to reduce the risk of getting a fake. You can check if your microSD card is authentic with the SD Insight app from the Google Play Store.

What Android's Adoptable Storage feature is all about

Android 6.0 Marshmallow added the Adoptable Storage feature that lets an Android device "adopt" a microSD card such that it acts like internal storage.

Adopting a microSD card lets Android install apps that support this feature on the card. The operating system decides which location to place apps and data - internal or adopted storage - based on the amount of remaining free space. However, improper removal of the adopted microSD card or a microSD card failure may lead to errors and data loss.

After a microSD card is formatted as adoptable storage by an Android device, it is encrypted and tied to that device.

It cannot be read by any other device.

If you change your mind after adopting a card, you can format the microSD card as Portable storage (which will erase all data), reverting it to external storage that can be removed without any consequences. Portable storage is limited to storing media like photos, video and music, but not apps.

When you first choose to adopt a microSD card, Android runs a test to measure the card's performance. Depending on the device manufacturer, you may be prevented from using the card if it fails the test.

Your device's internal storage is almost certainly faster than any microSD card in the market.

Thus, adopting a microSD card could lead to slower overall performance for the device. However, this trade-off may be worthwhile for devices with paltry internal storage.

The new A1 class rating was introduced by the SD Association to help you choose microSD cards that are suitable for apps.

While Adoptable Storage is part of the Android system, this feature may not be implemented by all device manufacturers.

For instance, it is more likely to be found in entry-level smartphones than flagship models because the former usually have very little internal storage.

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A version of this article appeared in the print edition of The Straits Times on July 05, 2017, with the headline A1 memory cards best fit for mobile devices. Subscribe