How to buy the best SD card for your camera, phone, tablet

Memory card speed, class, and capacity differences explained.

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Finally, the test revealed yet another factor that comes into play with SD media: the memory bus of your device. We expected the 90MBps 256GB SanDisk Extreme to blow away the 400GB SanDisk Ultra, which while not specifying its maximum speed rating, is but a U1 card. The fact that the two performed so closely has less to do with the SD and more to do with its host—the camera. The 2015-vintage Sony Alpha R7 II apparently uses a very old USB 2.0 bus coupled with a large buffer, so it can basically never exceed about 35MBps writes. We know this from extensive testing Alik Griffin has done on the Alpha R7 II. Paying extra for 90MBps would be a waste.

Granted, having a faster card does mean you can move the pictures to your computer much faster, but that’s probably not as important as write speeds in the camera itself.

To confirm our hypothesis about the camera bottleneck, we used a SanDisk UHS-I USB adapter to write a single 6GB 4K video file to each of the cards from a laptop. The 256GB SanDisk Extreme was at or around its rated 90MBps write speed, while the 400MB SanDisk Ultra wrote at about 40MBps. The two remaining SanDisk cards were obviously much, much slower, with writes at 10MBps or less. Each card was formatted prior to testing, using the exFAT file system.

sd card file write IDG

We timed how long it took to write a single 6GB file to each microSD card from a PC.

The upshot for DSLR photographers focused on still photos is to pay for a card that can write at close to the maximum write speed of your camera. The 3-year-old Sony camera obviously has a serious limitation, but a camera produced in 2018 or 2019 is unlikely to be as hindered.

Look for the rated write speed of the card. You won’t always find one, but the good news is, cards that can hit high write speeds usually like to brag about it on their packaging.

What’s the best SD card for an Android phone or tablet?

When it comes to an Android phone or tablet, you can pretty much give up on using speed class or write speeds to choose a memory card. While video cares about uninterrupted minimum speeds and still photography cares about maximum write speed, the designation that concerns running applications from a card is “Application Performance Class,” expressed as Class 1 (A1) and Class 2 (A2) markings.

These specs ratify a minimum sustained sequential write speed of 10MBps, and more importantly for application use, a minimum random read and minimum random write performance.

img application SD Association

For tablet or phone use, better random read and random write speed is more important if you intend to run an app from the card.

This is typically measured in IOPS (input/output operations per second) and indicates how fast a card can read and write bits from different areas of the memory card.

Unlike video and photo reads and writes, which are mostly sequential, application use from a card tends to jump around. Higher IOPS improves app performance.

Tested: Why A1 and A2 probably don’t even matter

While memory cards are typically tested in a PC with Windows-based storage tools, we wanted to see if we could detect a difference in the place the cards would be used: a phone. We used an LG V40 ThinQ phone with the Qualcomm SnapDragon 845 SoC running Android Oreo, and AndroBench 5.01 to measure the performance of each of the cards—an A1 card, an A2 card, and two cards that lack any such class marking (as noted in the chart below).

We did not test the cards using Android’s Adoptable Storage, as the V40 doesn’t offer the option, nor would it allow AndroBench to run its tests. Each of the cards was formatted in the phone prior to use.

The results between the A1 and A2 cards were mixed. In random reads, the A1-rated SanDisk Ultra 400GB came out in front by about 30 percent. In the perhaps more critical random write performance, the A2-rated SanDisk Extreme performed best.

sd card random read IDG

Random reads saw the A1-rated SanDisk Ultra 400GB ahead of the pack. The surprise is the underwhelming performance of the SanDisk Extreme 256GB.

But even there, the Extreme card’s performance was underwhelming. That’s due to the same issue we had in our DSLR tests above: the hardware.

sd card random write IDG

Random writes were better on the faster SanDisk Extreme, but nothing to write home about.

Technically, the SanDisk Extreme is rated for almost four times the random-write speed as the SanDisk Ultra, but to achieve that, you need hardware and firmware that fully supports the newer A2 specification. Today, there are no known Android phones or tablets that support the 2016-era SD 5.01 specification. Even worse for those hoping to use a 400GB microSD card to host apps—today’s phones don’t even support A1 yet.

In fact, the Qualcomm SnapDragon 845 SoC inside the V40 and other premium phones only supports SD version 3.01, which was passed in 2010. The App Performance specs for A1 and A2 were passed in 2016 with version 5.1.

Even worse: We ran AndroBench on the V40’s 64GB of Flash storage and saw about 15 times the performance of the SanDisk Extreme in random reads, and about nine times that card in random writes. 

The practical upshot is that if you want to store apps on your microSD card and get more performance, an A1 card can’t hurt. It’s likely to have have higher random performance than one without a rating, though your phone’s limitations may not allow it to reach its full potential. And yeah, it’s just not worth paying a premium for an A2 card just yet.

The two caveats here are if you want to use the card primarily for storing media for consumption, or for capturing your own videos. If you want to, say, copy 128GB of MP3 and video files to the SD card to watch or listen to, you may want to pay for a card with faster write speeds, such as this 100MBps SanDisk Ultra. This will greatly cut down how long it takes to copy the media to the card on your PC or your mobile device. If you plan to use your device for capturing video on a regular basis, you should probably follow the same guidelines from the video section above—a Class 10 works in most cases, such as this Kingston Canvas Select

Best Memory Card for Nintendo Switch SanDisk

SanDisk’s officially licensed memory card for the Nintendo Switch isn’t worth it as comparable cards can be had at a lower price.

What’s the best SD card for a Nintendo Switch?

Nintendo’s own guidance is to use a UHS-I card with a “transfer speed” of 60MBps to 95MBps (UHS-I is not to be confused with the U1 or U3 Speed Class markings, which just mean minimum write speeds of 10MBps and 30MBps, respectively). Nintendo also says that “the higher the transfer speed, the better gameplay experience on Nintendo Switch.”

That’s likely meant to lower the load time of games, which can be fairly large (Take-Two’s NBA 2K19, for example, is 31.5GB), although the average Nintendo Switch game is under 3GB in size.

Nevertheless, the UHS-I bus supports multiple maximum performance modes: 12.5MBps, 25MBps, 50MBps, or 104MBps—and it’s unclear which mode the Tegra X1 in the Switch uses. In our tests below, we found very little difference between a SanDisk Extreme with a 160MBps maximum read speed and our basic SanDisk card with a 45MBps maximum.

For most gamers, we think it boils down to capacity first with explicitly stated read performance a very close second for the best experience on the Switch. Note: Cards often don’t state their read performance unless it’s worth touting, so if you want to ensure your card doesn’t fall below the maximum potential, you’ll probably end up with something a little overkill in this department. 

Since the card is not primarily for video, the Class, U-, and V-ratings don’t matter much. And since Tegra X1 is likely limited to version 3.01 of the SD specification, A1 and A2 ratings aren’t relevant, either.

If you’re a serious Safety Sally, you can go ahead and buy an “official” memory card, such as the 128GB SanDisk Nintendo Switch. It’s rated for 100MB/s read and 90MB/s write speeds and carries U3 and V30 markings. But it can cost as much as $35 on Amazon. Alternatively, you could save some money by opting for a 128GB SanDisk Ultra card with a 100MBps read speed—you’d save about $15 and probably never notice a difference.

Tested: Memory card performance in the Nintendo Switch

Rather than go off our gut instincts we decided to look at one aspect of game experience: level loads. We installed the 21GB game Doom on each of the memory cards used in our previous tests above and then timed how long it took to open the level Resource Operations.

We averaged three level loads and restarted the Switch between runs. The results, as you can see, are pretty underwhelming. The four cards used in the tests range from yuck to yum, but the Switch doesn’t care all that much what it eats.

The reason? Level loads for a game aren’t always about sheer read performance. They can often be CPU intensive as texture assets and sound assets are decompressed before game play can begin.

The basic upshot is that a faster memory card can indeed lower the level loads and game starts, but probably not by much.

Best SD Card for Nintendo Switch? What’s cheap IDG

What’s the best memory card for a Nintendo Switch? The cheapest and largest probably.

What’s the best SD card for a dash cam or nanny cam?

If you just bought a dash cam and are eyeing a card that simply offers the most capacity for the price, you might be making a huge mistake. That’s because memory cards actually have a limited lifespan. While DSLR or action-cam usage is unlikely to hit that limit, a surveillance or dash cam is a different story.

Take your average cheap Black Friday-special card and drop it in a dash cam and it just might quit in a few months. In a crash cam or surveillance cam, that’s a disaster.

The answer is a “High Endurance” card, which is purpose-built for heavy use and harsh environmental conditions.

transcend high edurance Amazon

If you’re buying a microSD card for a dash cam or surveillance, it’s recommended that you opt for one rated for “high endurance,” to keep it from dying at a critical moment.

The 32GB Transcend High Endurance card, for example, is rated for 6,000 hours of 1080p video before possibly quitting. Endurance on these cards usually increases with capacity, so the same Transcend card at 16GB is rated for 3,000 hours, while the 64GB version is rated for 12,000 hours.

Transcend attributes the lifespan to its use of higher-performance MLC NAND, which is a less data-dense version of memory. Competitors such as SanDisk say MLC isn’t the only answer—firmware and controller NAND matter too. Although SanDisk doesn’t disclose its memory type (we believe it to be 3D TLC) the company’s own 64GB High Endurance memory card is rated to live for 10,000 hours, and 5,000 for the 32GB version. Again, the recommended course of action is to buy what your dash-cam maker recommends. If you don’t know, a high-endurance memory card makes the most sense.

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