Question Asrock X99 Extreme 4, how to set primary GPU.


Jun 23, 2016

I have a PC since 2016, built on an Asrock X99 Extreme 4 mobo, i7 5820k (I don't think it matters) and an Asus GTX 960 strix. All these years I had the 960 put in PCIE 1 slot. Some days ago I bought a Zotac RTX 2070 blower, with the intention to install it together with 960 and use them in the following manner: I installed RTX 2070 in PCIE 1 slot and as I removed the GTX 960 from that slot, I now installed it in PCIE 3 slot. I connect my monitor (LG 24MP57VQ-P 24'') to both cards, using HDMI for the 2070 and VGA (with DVI-I adaptor) for the 960. So when I want to game, I use nvidia control panel and set 2070 as active gpu and change my monitor to HDMI input and when I want to use 2070 as CUDA renderer, I set 960 primary and I change monitor's input accordingly to VGA (so everything I see in my screen is rendered by 960) and then I have 2070 gpu and vram totally free and 100% available only to be used for rendering. It works, I just have some questions.

When I boot, for some reason motherboard uses gtx 960 to show post messages or bios. I remind you that 960 is now installed in PCIE 3 slot. so if I have my monitor input set to HDMI and I boot, I see nothing until windows logon screen, because if in windows 2070 was set as primary then of course it will use 2070 to render the windows environment. And I found no option in Asrock bios to try and force it to use 2070. If I unplug my monitor from 960, then post and bios show correctly on 2070 (HDMI connection), but if I plug back the monitor to 960 too, again it chooses 960 (VGA connection). Now you'll tell me, if everything is working, what is the problem if it uses 960 to post? Well, problem or not, there must be a way to set things according to what you want and anyway I am curious as anybody would be what causes mobo to choose a PCIE 3 slot card as primary instead of the PCIE 1 slot card. I just don't get it but if there is a way to change it I will do it.

Windows also puts 960 first in device manager and in nvidia control panel. Even though it shows in nvidia control panel information that 2070 is plugged in PCIE 1 and is gen3 x16 and 960 is plugged in PCIE 3 and is gen3 x8. But regarding the order of the 2 gpus, it puts first 960 and second 2070.

Thanks for your time.
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