Tech

SD Express: Memory cards with PCIe 4.0 come close to high-end SSDs

The SD Association has published the SD 8.0 card specifications, which quadruples the maximum transfer rate compared to SD 7.0 to just under 4 GB / s. The SD Association provides for the use of two PCI Express 4.0 lanes including NVMe protocol. Corresponding memory cards are similar in terms of transfer speed and connection to current high-end SSDs such as Samsung's SSD 970 Evo Plus – only expensive models with four PCIe 4.0 lanes are even faster.

SD 7.0 has so far been limited to using a single PCIe 3.0 lane for just under 1 GB / s. The later specification extension SD 7.1 contains SD as well as micro SD cards, which are not yet considered by the successor. As an intermediate step sees the SD 8.0 specification also the use of a single PCIe 4.0 lane for almost 2 GB / s. Alternatively, manufacturers can use two PCIe 3.0 lanes or operate an SD Express card with PCIe 4.0 in a PCIe 3.0 mode.

Visually, SD cards only differ from previous versions when using two PCIe lanes (whether 4.0 or 3.0): the wider interface requires a third row of pins on the back of the card. Even the fastest SD-Express models remain fully downward compatible, so they work in conjunction with age-old controllers – but the transfer rate then drops to 12.5 Mbytes / s at worst. The other way around, coming SD-8.0 controllers can also handle old memory cards.

SD Express cards with two PCIe lanes have a third row of pins (see right).

(Image: SD Association)

SD-Express cards are useful for cameras, for example to film in 8K resolution with a high refresh rate or to be able to take more pictures per second in RAW. Upcoming game consoles from SD Express could also benefit, for example Nintendo is using SD cards for the Switch.



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It will still take years before memory cards with 4 GB / s come onto the market. So far, not even SD-7.0 versions with 1 GB / s are available. Experience has shown that camera manufacturers take even longer to use newer controllers.


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. (tagsToTranslate) SD 8.0 (t) SD Association (t) SD card (t) memory cards