I have a Mac Pro 5,1 with ElCapitan and HighSierra installed. I've upgraded the GPU to a Sapphire PULSE Radeon RX 580 8GB GDDR5, so that I can upgrade the HighSierra partition to Mojave. The card works fine when booted into HighSierra, but the display is pretty messed up when booted into ElCapitan - the screen slowly redraws any time I move the mouse at all, so pretty unusable. (With a 30" Apple Cinema HD Display).
I gather that some of the "metal" graphics cards are not supposed to be compatible with ElCapitan, but I wonder if there's some workaround (e.g. install HighSierra drivers into ElCapitan ?).
P.S. In case it helps someone ... I got around the absence of a boot screen on the RX580 by installing a third party boot manager called rEFInd-GOPFix (https://github.com/dakanji/Refind-GOPFix/releases/tag/v0.12.0.B).
I gather that some of the "metal" graphics cards are not supposed to be compatible with ElCapitan, but I wonder if there's some workaround (e.g. install HighSierra drivers into ElCapitan ?).
P.S. In case it helps someone ... I got around the absence of a boot screen on the RX580 by installing a third party boot manager called rEFInd-GOPFix (https://github.com/dakanji/Refind-GOPFix/releases/tag/v0.12.0.B).
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