UE5 uses virtual textures. Each object has 8K source textures on disk, but only the parts of those textures that are visible and drawn are required. In a perfect VT engine, you need one texel per pixel, so 1440p would be 3.7 million pixels needing 3.7 texels. I can't remember what maps Epic said they were using, so for illustration let's say 10 bits per pixel for textures. That'd be 37 megabits, or about maybe 5 MB per frame. At 60 fps, if you were refreshing every single texel, that's 300 MB/s tops. However, use of texels is largely shared across frames, so reality is far less than that. You also store tiles including multiple used texels, so RAM requirements are higher than just 5 MB but streaming requirements are much lower.
The game Trials HD used VT at 720p. The calculations for that are on this forum and Sebbbi stated IIRC 7 MB/s. 1440p is 4x that, so 28 MBs doing the same thing trials was.
This is the joy of virtualisation. The old way of rendering graphics was keeping it all in RAM and only using a tiny part of that dataset per frame. Virtualisation allows you to just keep the parts in RAM necessary for what you see (and are about to see). It introduces a huge efficiency in data requirements by reducing the working set. The upside is far, far smaller RAM footprint, allowing more variety etc. The cost of this is higher steaming requirements, but that dataflow isn't particularly bandwidth intensive for the amount of geometry you get to see.
Conceptually, it's like foveated rendering. there's no point drawing the bits of the screen in high fidelity if your eye can't resolve them, so render just the smallest portion your eye is looking at in high quality and render the rest in low. the result is exactly the same but you reduce rendering requirements to a tiny fraction. Here, don't bother storing all the vertices (or texels) if you aren't using that data anytime soon. The future of rendering is moving towards efficiency, which is one of the key arguments some of us have raised over the raw TF comparisons with next-gen consoles over current-gen. Better ways of using the Flops means doing more work for the same raw resources. We're working smarter, not harder, and that evolution is happening all-round in the computing space.
