A very noticeable feature is that USB4 can tunnel USB3, which means it works like an USB hub, instead of an external PCIe USB controller (like in Thunderbolt). USB2 is still just physically separately transported over the D+/D- pins.
USB4 actually provides both USB 1/2 and 3 tunnelling, but it's incorrect to say it behaves like a hub because it involves needing an appropriate endpoint on the other end. Effectively a virtual cable, iirc, though there are at least two different mechanisms.
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A very noticeable feature is that USB4 can tunnel USB3, which means it works like an USB hub, instead of an external PCIe USB controller (like in Thunderbolt). USB2 is still just physically separately transported over the D+/D- pins.
USB4 actually provides both USB 1/2 and 3 tunnelling, but it's incorrect to say it behaves like a hub because it involves needing an appropriate endpoint on the other end. Effectively a virtual cable, iirc, though there are at least two different mechanisms.