SD Association announces microSD Express standard

The SD Association has officially announced the microSD Express standard, which brings PCI Express and Non-Volatile Memory Express (NVMe) support to the microSD form factor, while Micron and Western Digital push the limits of SDXC capacity with rival 1TB cards.

Part of the latest Secure Digital 7.1 standard, microSD Express offers full backwards compatibility with existing microSD standards but with the addition of PCI Express and Non-Volatile Memory Express (NVMe) connectivity. Providing both the card and the host device support the new standard, dubbed microSD Express, data rates are pushed up to a peak of 985MB/s, while the NVMe protocol provides advanced memory access capabilities out of the reach of current microSD implementations.

'MicroSD Express gives the mobile industry a compelling new choice to equip mobile devices with removable SSDs,' claims Hiroyuki Sakamoto, president of the SD Association. 'SD 7.1 prepares consumers and mobile device manufacturers to meet ever increasing storage demands for years to come.'

The microSD Express standard implements the PCI Express 3.1 and NVMe 1.3 specifications on a secondary row of pins, while retaining backwards compatibility with existing microSD cards on its primary pins. The SD Association claims that in addition to the improved data transfer rates, microSD Express cards will draw less power than their legacy equivalents.

The overall concept isn't new: Full-size Secure Digital cards received the SD Express standard back in June 2018, with the new revision simply shrinking the technology down to the more portable microSD form factor. The microSD Express standard also has the same drawback as its full-size equivalent: By co-opting the second set of pins for PCIe and NVMe use the cards lose the ability to support Ultra High Speed II and III (UHS-II and UHS-III) communication, dropping their maximum speed when microSD Express cards are used in non-Express readers or vice-versa from 624MB/s to just 104MB/s.

A decade on from when a 16GB microSD card was a notable achievement, meanwhile, both Micron and Western Digital have announced cards with a whopping 1TB capacity. Based in both cases on the microSDXC UHS-I standard, Western Digital's variant has the edge in performance with a claimed peak 160MB/s read and 90MB/s write speed to Micron's 100MB/s read and 95MB/s write.

Western Digital is also the only one of the pair to put a launch date and pricing to its products, promising that the SanDisk Extreme-branded card will launch in April for $449.99 (around £340 excluding taxes) while Micron's is scheduled for some time in the second quarter at an as-yet unspecified price. The SD Association, meanwhile, has not offered a timescale for SD Express nor microSD Express implementation in consumer devices.