4 ms·
> mark the speed on the USB ports, removing ambiguities Unfortunately it's not true. Quiz: what happens when a device capable of 20Gbps is plugged into a port
by riobard 5mo ago
> mark the speed on the USB ports, removing ambiguities
Unfortunately it's not true.
Quiz: what happens when a device capable of 20Gbps is plugged into a port marked as 40Gbps?
- ziml77 5mo agoI can't tell if this is a trick question that has something to do with a quirk of USB running multiple lanes in parallel to get higher speeds. Because if not then it's the same as any specification for connecting devices that allows for multiple speeds. It runs at the lowest of the max speeds supported of everything in the chain.
- riobard 5mo agoThat's exactly the issue. I'm just pointing out that it's a fantasy to hope for simple numbering of max supported speeds will simplify the current USB mess. It will not. Consumers would expect plugging a 20Gbps device into a 40Gbps port should result in 20Gbps negotiated speed. In reality it will mostly likely end up at 10Gbps (or less) because of the mess.
- adrian_b 5mo agoOlder Thunderbolt devices were not compatible with USB, so plugging them into an USB Type C port would not work. Newer Thunderbolt/USB 4 devices do not have any technical reason for preventing them to work as USB 3.2 2x2, i.e. to work at 20 Gb/s when plugged into a 20 Gb/s host port, and vice-versa for 20 Gb/s devices plugged into a USB 4/Thunderbolt host port, because both Thunderbolt and 20 Gb/s USB need the same wires in the cable and connector. I do not know if all USB 4 controllers also work at 20 Gb/s (USB 3.2 2x2), but if they do not work that should be considered a bug.
- eqvinox 5mo agoUSB4/TB4 devices doing (only) PCIe tunneling will absolutely not work on a USB3.2 port, or even on an USB4 port without PCIe support (which you can find on some very recent smartphones I believe. It's spec compliant, PCIe is optional.)
- deleted 5mo ago[deleted]