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What is microSD Express and why is it important?



  Sample labeling for microSD Express cards.
SD mapping

SD Cards ̵

1; Everyone has a few, but nobody thinks much about it. That's proof of how well they work. But performance is always important, and microSD Express promises to make microSD cards much faster.

What happened to SD Express?

Announced in February 2019 as part of the SD 7.1 SD Association specification, microSD Express follows its bigger brother, SD Express, which landed in mid-2018 with a thud. SD Express cards were not launched this year, although the standard had promised four to five times the performance of the current SD cards. Now, with microSD Express, we could finally get lightning fast expansion cards for our laptops, smartphones and cameras.

It's not clear why nobody got excited about SD Express. Perhaps most companies were waiting for the introduction of the microSD version before they got serious. This is likely to be the case because of the emergence of early microSD Express cards at trade conferences as well as new card readers and firmware controllers that support both versions of SD Express.

There's nothing to buy yet, but that should change the not-too-distant future.

What is microSD Express?

  The logos PCIe and NVMe.
SD mapping

microSD Express is a smaller version of SD Express. These are new types of SD cards that support a maximum read speed of 985 megabytes per second (MB / s). Current microSD cards do not even reach 200 MB / s in comparison. The Express versions of SD use the PCIe 3.1 interface and NVMe. These are the same technologies used by fast M.2 solid-state drives in PCs. However, the new Express cards only use one PCIe lane, while M.2 NVMe drives typically use four.

The smaller microSD cards make it easier (literally) to use SD cards in phones and tablets and laptops. The only exception is digital cameras, which prefer full-size SD and CompactFlash cards.

What has changed?

In 2019, companies took action. Standards organizations can create all the new specifications they want, but if companies do not turn them into real products, it's just ideas.

For example, PCIe 4.0 was announced in 2017, but it was only with new products for reality PCs in 2019 (on time to announce the PCIe 5.0 specification). SD Express has a similar problem with slow adoption by device manufacturers and SD card manufacturers.

What hope does microSD Express have? For one thing, Western Digital (owner of SanDisk) demonstrated a SanDisk microSD Express card at Computex 2019 in Taiwan. The company has not announced a release date for the card, but the fact that it exists is promising.

  Test results that compare the speed of microSD Express with that of a recent microSD card.
microSD Express is considerably faster than the current microSD cards. Western Digital

WD showed the prototype of a card that carried a large video file of about 13 GB. During the file transfer test, WD indicated that the microSD Express card was able to transfer the file in less than 30 seconds. SanDisk compared this with the SanDisk Extreme UHS-I, which performed the same job in just under 2 1/2 minutes. This speed is about five times higher than that of current microSD UHS-I cards.

WD also worked with technology designer JMicron to create an early version of an external microSD card reader that you can connect to a PC via USB. This reader uses the same SanDisk microSD Express card. A benchmark tool achieved a read speed of 820 MB / s and a write speed of 475 MB / s. In short: When used with an internal card reader, it ran in the external reader similar to the microSD Express.

While these results sound promising, a company is doing everything in its power to make the most of its products in demonstrations. We want third parties to confirm WD's speed claims through independent testing before we put too much emphasis on those results.

In addition to WD's work, firmware maker Phison used its SD Express and microSD Express controllers, the PS5017. A controller is an essential low-level component that supports the communication of computer parts. Phison's work is still in its infancy and many improvements are needed. Cards up to 512GB are currently supported, though SD Express and microSD Express are expected to support up to a whopping 128 terabytes. This is more future proof than our current reality, but there are already SD cards with a capacity of 1 TB. So it is strange that a controller with about half of this capacity comes on the market shows some tendency in the industry to introduce the new SD card type.

More changes are needed

Although we do not think much about memory expansion cards, the benefits of faster storage make a big difference. If microSD Express delivers what it promises, it means better performance of our devices.

For laptops with a compatible card reader, the new speed means you could use microSD cards as secondary drives because their responsiveness and capacity would be so high. Many people are already using microSD cards, but performance degradation is noticeable on large file types. The new version of microSD Express should improve this to the extent that expansion cards work as fast (or faster) as 2.5-inch SATA-III SSDs.

Mobile phones are likely to lag behind in implementing microSD Express. They need new hardware to read the cards, as do laptops, but phones have a harder time dealing with potential heat problems than PCs and external devices. The faster you create a specific technology, the more heat is generally generated – even for non-moving parts. Lightning fast PCIe 4.0 M.2 SSDs, for example, rock massive heat shields to stay cool.

In this Computex video from WD, the external microSD Express reader is placed in front of a PC fan. This suggests that heat issues are currently a problem. And you can not put a fan in a smartphone – at least not most. Hopefully, all of this will be resolved in the coming months, and we'll find that microSD Express cards support devices that do so, dramatically speeding it up.


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