With SD Express technology, which is based on NVMe and PCIe, you will eventually be able to buy an SD card with speeds nearing 4GB/s.
The SD Association said that SD Express uses the well-known PCIe 4.0 specification and the latest NVMe specification (up to version 1.4) defined by PCI-SIG and NVM Express, respectively. SD 8.0 specification provides two transfer speed options for SD Express memory cards.
“The two transfer speeds are accomplished by supporting either PCIe 3.0 x2 or PCIe 4.0 x1 architectures with up to ~2GB/s and with PCIe 4.0 x2 technology with up to 4GB/s. SD Express cards offering PCIe 4.0 x1 architecture use the same form factor as defined for SD 7.0 specification cards with the second row of pins to deliver transfer speeds up to 2 GB/s. SD Express cards supporting dual PCIe lanes (PCIe 3.0 x2 or PCIe 4.0 x2 technologies) have three rows of pins”, the Association announced.