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The SD 9.1 specification brings support for microSD Express cards with speeds up to 2GB/s, or twice the previous top speed introduced in the SD 9.1 spec. It does this via a PCIe Gen4 x1 lane. The SD Association has also unveiled four new SD Express classes with minimum speeds ranging from 150 MB/s to 600 MB/s. https://www.businesswire.com/news/home/20231019426797/en/microSD-Express-Doubles-Speeds-New-SD-Express-Speed-Classes-Introduced #SDCard #SDExpress #SDAssociation #Storage

Adata Launches SD Express Cards, A Format No Camera Supports

Adata has announced that it will be producing a line of SD Express memory cards, following Lexar which did the same earlier this year. It's unclear who these cards are for, however, as no manufacturer currently supports the spec.

Adata is a Taiwanese memory and storage manufacturer that has been operating since 2001, but it hasn't done much -- if anything -- in the memory card space in that time. The company has thus far focused on solid-state drives for personal computers as well as external storage solutions but appears to be ready to break into memory cards with the launch of its SD Express line.

PCWorld reports that the company will release what it is calling Premier Extreme SDXC SD 7.0 express cards that will use PCIe Gen 3 and promises read and write speeds of 800 MB/s and 700 MB/s respectively. The company also points out that these speeds are about 1.5 times faster than a standard SATA SSD, but up to eight times faster than a standard SD card.

SD Express is the SD Association's answer to CF Express, a card format that has three types and is already in use across the camera industry from stills photo cameras to video-focused cameras. Manufacturers were quick to sign on to the standard several years ago and notably Canon, Nikon, and Sony all signed on and currently support the standard across a range of devices. Sony, in particular, has been a strong supporter of the Type A standard, which is capable of half the read and write speeds of the larger Type B standard but is also much smaller -- A CFexpress Type A card is smaller than a typical SD card while a CFexpress Type B card is slightly larger than an SD card.

A common misconception is that SD Express is fully compatible with current devices that take SD cards. While the cards are technically backwards compatible, that statement is misleading since SD Express uses a different bus than current SD cards. SD Express uses the PCIe bus while current SD cards use the UHS bus. When an SD Express card is placed into a current-generation device's SD port, it can take advantage of a single lane of UHS but as a result will max out at UHS-I speeds, which caps at about 104 MB/s.

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Because of this glaring limitation, it's unclear why Adata or Lexar are building on the SD Express specification as PetaPixel sources confirm that to date, no manufacturer has signed on to produce any hardware that fully supports the format, meaning the best anyone can expect to get out of what will be more expensive cards is current UHS-I speeds. Additionally, there are no card readers on the market that can take advantage of the top speeds promised for SD Express, either. There is literally no hardware anywhere that supports these cards.

The main argument that most make against CFexpress is that it requires the purchase of both new cards and new readers, but SD express has those same limitations. Additionally, SD Express has theoretical speed caps that are well below the CFexpress theoretical limits. Current Type B cards typically reach read speeds of 1,700 MB/s and surpass 1,400 MB/s write speeds thanks to their two lanes of PCIe. Type A cards are slower due to their single-lane design, but still promise 800 MB/s read speeds and 700 MB/s write speeds which matches what SD Express is touting. The difference here is that CFexpress is actually supported and cameras and readers currently exist that use it.

What's more, CFexpress is likely to continue to grow in popularity as ProGrade Digital's recent choice to start manufacturing the cards shows it believes the format to be popular enough to warrant production costs.

Just as was the case with Lexar's SD Express announcement, Adata has not provided any information on when the cards will actually be available to purchase or how much they will cost. None of that really matters anyway, though, since no one can use the cards to begin with.

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Lexar Developing SD Express Memory Cards, But It’s Unclear Who For

Lexar has announced that it is actively developing on the thus far unused SD Express specification to create SD memory cards that use PCI Express (PCIe 4.0) and will more than triple the speeds of current UHS-II cards, but it's not clear who these cards will work for.

Lexar says that it is actively developing both regular SD Express as well as microSD Express memory cards. Its SD Express cards will have a capacity of up to 512 gigabytes while its microSD Express will cap out at 256 gigabytes.

Lexar SD Express and microSD Express memory cards will feature write speeds of up to 410MB/s and read speeds of up to 824MB/s, respectfully. Lexar is currently working with manufacturers of relevant host devices as part of its early development.

The SD Express specification is not new but was developed by the SD association several years ago in response to the Compact Flash organization's CFexpress specification. The idea would allow for the format to theoretically reach greater capacities and much faster speeds all while maintaining the same current SD card format with the promise of backward compatibility.

While this sounds great, the SD Express specification has not been actively developed for a reason -- it's not perfect. In 2019, PetaPixel spoke with ProGrade Digital's Wes Brewer who explained that there were many hidden drawbacks with the SD Express specification. For starters, SD Express cards would technically be backwards compatible, but only to UHS-I speeds.

“You can put it in there, and it’ll work, but it’ll only work as a UHS-I card," Brewer said. "So if the camera requires full SD UHS-II performance, it won’t work right. It won’t work as well as it’s supposed to like an SD UHS-II card would work.”

At the time, Brewer noted that no camera manufacturer was interested in the SD Express format and none were making any cameras that would work with it. To date, that has not changed and it's unclear who Lexar's cards would be for.

The SD Association's SDx specification allows for HC, XC and UC (high capacity, extended capacity, and ultra capacity) cards.

What's more, those looking to keep the SD form factor have already found a solution: CFexpress type A. Sony's latest cameras accept both standard UHS-II SD cards and CFexpress Type A cards in the same card slot. Back in 2019, Brewer predicted this.

In 2020, the specification was updated and allowed for transfer speeds for up to 3,983 megabytes per second, a huge leap in performance. It wasn't clear though if the backward compatibility issue had been solved nor if any camera or device manufacturer was even interested in supporting cards made with the specification.

Even if all the issues with SD Express were solved by the new specification and camera makers decide to support them, SD Express is a long way from challenging CFexpress. The read and write speeds promised on Lexar's coming SD Express cards may be up to three times better than UHS-II SD cards, but they are still well below current CFexpress speeds. Current Type B cards typically reach read speeds of 1,700 MB/s and surpass 1,400 MB/s write speeds thanks to their two lanes of PCIe. Type A cards are slower due to their single-lane design, but still promise 800 MB/s read speeds and 700 MB/s write speeds. While SD Express appears to be competitive on read speeds, Lexar's SD Express cards will only reach about half the write speed performance.

Lexar appears undeterred, however. The company plans to launch its new line of SD Express cards in 2022, but it is not clear what devices will support them or how much they will cost. That last note will be the most important, as SD Express may only be able to compete by undercutting the currently astronomical price of CFexpress.

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