The SD Association announced a new standard for SD Express and microSD Express that adds new speed classes for the former and promises double the speeds of the latter. While great on paper, the updates do nothing to make the format desirable for camera makers.
The SD Association is adopting the next-generation of PCIe standards to its specification, just as the Compact Flash Association did earlier this month with CFexpress 4.0. In doing so, the SD Association says that microSD Express can reach up to 2 GB/s (theoretical).
“The latest generation of microSD Express uses the PCIe interface delivering a 1,969 megabytes per second (MB/s), nearly 2 gigabytes per second (GB/s) speeds by using the PCIe Gen4 x1 lane,” the organization explains.
“microSD Express was introduced with 985 MB/s speed maximum data transfer rate and the NVMe upper layer protocol in the SD 7.1 specification. The increase in speed gives product designers more storage options and SSD level performance for a variety of size constrained devices requiring easily repairable or upgradeable storage.”
In addition to that speed bump for microSD Express, SD Express received new Speed Classes that guarantee minimum read and write performance. Designated by a rounded box with a large “E” on the left, the following number would promise 150, 300, 450, or 600 MB/s minimum transfer speeds.
“By defining minimum assured sequential performance standards for SD Express memory cards, the SDA helps both device manufacturers and consumers ensure the best recording and playback of all types of content,” Hiroyuki Sakamoto, president of the SD Association, says.
“We doubled the speed of microSD Express to 2GB/s to give product manufacturers more storage options capable of handling the most demanding storage uses making SD Express memory cards a compelling, ecologically sound choice making it easier to repair and upgrade devices.”
Great on Paper, But Changes Nothing Practically
SD Express looks great on paper, but it has never gotten further than that. Unlike how the Compact Flash Association operates, the SD Association hasn’t done much more than just take the next generation of the PCIe standard and announce a specification that supports it without doing anything more to assure that the standard can even be successful.
While the CFA seems to spend a great deal of time working with both memory and camera manufacturers to assure they can each support it, the SD Association doesn’t even make sure either side can support previous versions of a specification, let alone new ones.
This issue is compounded by the backward compatibility problem that SD Express made for itself — an issue PetaPixel has written about extensively. In short, these cards are only backward compatible in the sense they work, but not to the true potential of a card — it will only ever be as fast as UHS-I.
Another issue with SD Express is heat management. PCIe is great because of its speed, but the cards can get very hot. Because they are so thin, an SD card that attempts to run at the same speed as a CFexpress will get so hot the plastic will melt unless it is thermally throttled, which will drop performance and defeat the purpose of using PCIe to begin with.
That, in short, is why SD Express was dead on arrival when it was announced and remains deep in the ground to this day. Lexar said it was making SD Express cards two years ago, but those never came to market and the company hasn’t mentioned the format since. Cards from other manufacturers that have come to market have — unsurprisingly — not impressed.
Try as the SD Association might, the format lacks support from either the memory or camera manufacturers, and given the widespread adoption of CFexpress, that is very unlikely to change. The dream of SD Express remains just that — a dream.
Image credits: SD Association