While SD Express remains profoundly unpopular, the CFExpress standard (preceded by XQD) is the norm for mid-range and up cameras these days. And CFX is, just like you expected, simply a (well-specified subset of) NVMe SSD in a somewhat more robust case. CFX readers are generally just like the article describes the SDX USB reader: There's a chip in there which talks PCIe and NVMe to the SSD and emulates SCSI over USB (UASP) on the host side:<p>> Wait a second. USB3 doesn’t do Bus Mastering. Either there’s something wrong with the device description, or there’s some hardcore multiplexing of lines going on. But the reality was less exсiting — it uses a JMicron JMS581LT host controller chip, which implements PCIe root/switch/something at least partially, and communicates with the card over PCIe. But it doesn’t pass it to the host, and communicates with the host over 10 Gib/s USB. Interesting chip overall, but not interesting as a DMA target.<p>However, there <i>are</i> also Thunderbolt CFX readers. And those do actually hook up the SSD to the host directly.<p>> By the way, the photo camera probably doesn’t need the speed of PCIe<p>"need" is a curious question, if you're inclined to shoot RAW + JPG and let 'er rip at 20 frames per second (no shutter means no wear, after all!) you're producing around 1.5 gigabytes of photos... per second. (In practice, card write speeds seem to tap out at around 850 MB/s).