Resizable Base Address Register. In short, rather than the 256MB of mapped memory available to the CPU for any PCI device, ReBAR capable devices can map larger memory to the CPU’s addressable memory space. Without ReBAR or sufficient tricks (that Intel GPUs lack) you have to shuffle 256MB chunks around between GPU and CPU.
Using an Intel discrete GPU on a system that lacks ReBAR support results in somewhat lower performance, not a complete inability to use more than 256MB of VRAM.
Source? I don't know what happened for the Linux drivers, but the Windows drivers definitely booted and ran benchmarks without ReBAR when the Arc A380 launched, because there were lots of published comparisons of the performance impact on workloads that definitely didn't fit in 256MB.
Unfortunately I can't edit my earlier post, because I can't find it - might have been distorted rumour that reached me, then :/
Wasn't helped by my experience reacting very strongly to story of early Arc drivers being problematic because the devs were too used to GPU being just a ring-bus away ;-)
