Last June, the SD Association announced SD Express, an incredibly fast SD card standard that taps a PC’s PCI Express bus for speeds up to 985 Mbytes/s. Virtually no one adopted it. Now, the SD Association has tried again, applying the same spec to the much more popular microSD card form factor: microSD Express.
On paper, the SD Express standard should have succeeded. With support for both the PCI Express bus as well as the NVMe memory access layer, SD Express cards could have provided external removable storage about as fast as an internal SSD—great news for laptops. But the majority of laptops and smartphones (if they support removeable storage at all) use the more compact microSD form factor instead.
Now, microSD Express should combine fantastic performance with the popularity of the microSD form factor. It puts a single channel of PCIe into the microSD card itself, so that it can hit a bandwidth of 985MBps. That also means the standard should scale up in the future, so that it can support Gen4 (2GBps) and Gen5 (4GBps) specs. The SD Alliance also says the new cards will consume less energy than a regular microSD card, though with the same power tolerances.
Fortunately, microSD Express cards are also backward-compatible, meaning you’d be able to use them on older devices that support microSD cards, even if they don't support the new microSD Express interface. Those older devices wouldn’t be able to write data to the cards as quickly as a microSD Express-compatible device would, of course.
Here's how fast the new spec is. A tablet like the Microsoft Surface Pro 6 supports microSDXC cards, which are available in three speeds: UHS-I, -II, and -III. It's pretty rare to find UHS-II cards like this Lexar UHS-II 64GB card, with bandwidth of 300MBps. Nearly a gigabyte per second of bandwidth, like the microSD Express standard would provide, would be a significant jump.
Here’s what to look for
Right now, there’s a laundry list of SD and microSD cards and specs, each slightly different than the last. MicroSD Express cards are covered by the SD7.1 spec, so a phone or laptop that includes SD7.1 microSD card support should be covered by the microSD Express specification. Don’t bother shopping for a card or an SD7.1-compliant laptop just yet—none exist. But in the future, keep an eye out for either SD 7.1 support or the “Express” designation—those are the tipoffs to this faster spec.
Here are the microSD Express logos, as supplied by the SD Association:
What this means to you: Now that the SD Association has brought the high-speed PCIe interface to microSD, the stars may have aligned for a substantive increase in external memory performance. It remains to be seen, though, whether laptop makers will adopt the technology—and whether they’ll be able to market it to consumers, who will likely be unaware of its new capabilities.