Already 2018 the SD Association had presented the new SD Express specification in SD card standard 7.0, which provided for a maximum transfer speed of 985 MB/s via PCIe 3.0 - then in May 2020 via SD standard 8.0 even a speed of around 4 GB/s (3,938 MB/s) via two PCIe 4.0 lanes was defined (SD Express Gen4x2).
Now, memory card specialist Lexar has become the first manufacturer to announce the development of matching SD and microSD memory cards for SD Express Standard 8.0, which are said to offer a theoretical maximum read speed of up to 985 MB/s and thus transfer data three times faster than the fastest UHS-II SD card currently available. The Lexar SD Express memory cards use two PCle 3.0 lanes, utilize the NVMe Express (NVMe) protocol, and are backward compatible.
Lexar SD/microSD Express cards
As a controller, Lexar uses the SM2708 from Silicon Motion, which since recently supports not only the SD 7.0 but also SD 8.0 specification, but remains limited by its PCIe 3.0 x2 interface and can thus only achieve a theoretical maximum transfer speed of 1,700 MB/s.
Although Lexar speaks in the press release of a possible maximum data transfer rate of almost 4 GB per second according to SD 8.0, this is only the theoretical upper speed limit when using PCIe 4. 0 and is far from being reached in practice when reading or writing data from the SD Express cards: so the Lexar SD Express and microSD Express memory cards will reach speeds of only up to 824 MB/s when reading or 410 MB/s when writing, which is fast enough for recording and playing back 8K or RAW video, RAW continuous shooting or even 360-degree videos.
SD standards comparison
Why Lexar mentions the maximum SD 8.0 speed of 4 GB/s in this context therefore remains puzzling, perhaps referring to future SD Express versions, which will then have PCIe 4.0 interfaces. Although the new SD Express cards will also be compatible with older devices that use SD cards, their speed will then be limited to the maximum UHS-I speed of 104 MB/s.
SD Express and CFexpress 2.0 in comparison
Since new memory cards are useless on their own, Lexar is currently working with manufacturers of corresponding SD Express host devices and plans to launch them in 2022. Not mentioned, however, is the commitment of, for example, camera manufacturers to the new format, which is a competitor to the now quite established CFexpress cards, which, for example, www. slashcam.de/4K-Kamera-Vergleich-782e1cdb1f238939e7eb5388603657cb.html (used by the Sony FX6, A7S III, Canon EOS R5 and Canon EOS C300 Mark III), because without devices that use SD Express as a (recording) medium, SD Express threatens to be stillborn, especially since the first Lexar SD Express cards are not expected to hit the market until 2022. The Lexar SD Express memory cards should then be available with capacity options up to 512 GB, microSD Express cards in capacities up to 256 GB.
Wise CFexpress Type-B cards
CFexpress 2.0 cards are available in three formats: As compact Type A cards, which use one PCIe 3.0 lane and reach 1 GB/s, and in the future as larger Type C models with capacities of up to 4 TB and up to four PCI 3.0 lanes (more precisely 1,2 or 4) - depending on the number of lanes used, the speed also scales, which can then be 1 GB/s, 2 GB/s or (in the future) also 4 GB/s. However, the most common are CFexpress 1.0 cards in XQD and Type-B form factor (which use two PCIe 3.0 lanes with a maximum speed of 2 GB/s - these are used by the Canon EOS R5,Panasonic S1 with V-Log,Nikon Z6 and Nikon Z7 for example.
Canon EOS R5
Compared to this, SD Express with a maximum speed of around 824 MB/s and a capacity of 512 GB is still in its infancy - especially since the first models are not scheduled to appear until 2022. SD Express could only be successful if the sometimes very high prices of CF Express are significantly undercut - provided that camera manufacturers implement SD Express at all.
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