GROUP TEST: MicroSD cards
Storage is cheap, but sometimes it pays to choose wisely. Jim Martin explains how to choose a microSD card that’s right for your needs and rounds up your best options
Just about everything with a memory card slot takes microSD these days. From phones and tablets to action cameras, dash cams and drones: they all use microSD for storage. Just any old card won’t do though, especially if you’re trying to record HD or even 4K video. Over the following pages we explain how to choose a microSD card that’s right for your needs.
First of all, it’s important to understand microSD standards as well as all the markings. There are different types of microSD card, even if they look identical.
The first is microSDHC. The HC stands for High Capacity is covers sizes from 4- to 32GB. Above 32GB is microSDXC (XC stands for eXtended Capacity), and the largest card you can currently buy is 200GB. However, the latest phones, including the HTC 10, claim to support microSD cards up to 2TB. Check your device’s support before buying a card: many dash cams don’t support SDXC, so are limited to 32GB.
There are three different standards for speed, and you may see more than one on a card. The original speed marking was a number inside the letter C (middle in the image, left). The number denoted the minimum sustained write speed, so a ‘Class 6’ card would be capable of writing at 6MB/s – six megabytes per second. That’s a sequential write speed, so it only applies when writing large amounts of data (such as
when recording video) in sequential memory cells. It doesn’t apply to random 4KB writes, which is the typical use in a phone or tablet when small amounts of data are written to random locations.
Many devices which record HD video demand a Class 10 card, but most Class 10 microSD cards are capable of much more than the minimum of 10MB/s write speed.
This is where the UHS system comes in. It stands for Ultra High Speed, and uses a number in the letter U to denote the class. A UHS class 1 card writes at a minimum of 10MB/s and a UHS class 3 card writes at a minimum of 30MB/s.
You may also see UHS-I or UHS-II on the card. This tells you which technology the card uses. The UHS-I ‘bus’ can operate at up to 104MB/s, while the UHS-II bus can transfer data at up to 312MB/s. This doesn’t mean the card will read and write at those speeds, only the maximums.
In order to benefit from the higher speeds available with a UHS-I or UHSII microSD card, you’ll need a device that’s compatible with this standard. You can easily spot a UHS-II card as it has a second row of pins underneath the main set. All the cards on test here are either Class 10 or UHS-I.
There’s a new speed class system, called the Video Class. You’ll start seeing this on cards soon, as a V with a number beside it. Like the original Class system, it denotes the minimum sequential write speed in MB/s and ranges from V6 up to V90.
The SD Association recommends the following classes of card for recording at different video resolutions:
Temperature, X-ray and shock-proof
MicroSD cards are tiny and easy to lose, but in addition to buying a carry case for your collection, it’s important to choose cards that will survive travelling and any other factors which threaten their operation.
Some manufacturers state that their cards are water-proof and also X-ray proof. However, these are characteristics of pretty much all microSD cards. Data isn’t stored magnetically, so airport scanners shouldn’t pose a problem, and as long as you’re not trying to read or write data to the card in a non-waterproof card reader underwater, a microSD card should shrug off getting wet.
Cards can also be rated to survive in certain temperatures, say from -25 to 85ºC, be ‘shock’ proof and more. As long as you’re not paying more for such cards, there’s no harm in buying one of these cards so that you can claim on the warranty if it fails because it got too hot or was vibrated too much. Quite how you would prove the cause of failure is another matter.
Warranty, therefore, is more important than any of these things: check not only the duration but also the terms but also what it covers.
Which cards to buy
Our recommendation is to stick to the wellknown brands, which will offer a warranty on their cards. Reputable companies include: Toshiba, Samsung, SanDisk, Lexar, Kingston and Verbatim, among others.
There are plenty of fakes and counterfeit microSD cards, so make sure you buy from a trusted seller. If you see a card on eBay that’s a lot cheaper than you expect it to be, there’s probably a reason. Before you buy a card, check the maximum capacity of your device. Some are limited to 32GB as they are SDHC, not SDXC. It’s tempting to get a 128GB card for under £30, but it won’t work if your device can’t access it.
If you’re buying storage with the intention of recording 4K video, go for a card that’s UHS-I Class 3 rated. Many also recommend the same if you’re recording 1080p, especially at high frame rates.
It’s hard to buy using specifications, as it’s the small-file transfer speeds, which make a difference here.
Many devices which record HD video demand a Class 10 card, but most Class 10 microSD cards are capable of much more than the minimum of 10MB/s write speed
The requirements are similar to drones and action cameras, but you’ll tend to find dash cams are less demanding when it comes to write speeds. Most manufacturers recommend a Class 10 card or better.
How we test
We use CrystalDiskMark to test the read and write speeds of each card. This tests both the sequential speeds (reading and writing large blocks of data) and small-file performance, using 4KB reads and writes.
Tests are carried out on our Intel Core i7-based test rig over USB 3.0. We use the full-size SD adaptors which come with cards and a Lexar Professional USB 3.0 Dual-Slot Reader. If a card comes with its own USB 3.0 adaptor, as with Lexar’s own card, we use that instead.
UHS Speed Class Bus Speed Speed Class
UHS-I UHS-II Minimum sequential write speed Card image 90MB/s 60MB/s 30MB/s 10MB/s 6MB/s 4MB/s 2MB/s Speed Class UHS Speed Class Video Class Speed Corresponding video format Speed Class The necessary speed varies by each recording/playback device condition, even in the same format