Only 3 monitors working

[Sporkyzz]

Anyone have a clue why i can only get 3 monitors to work? When i click the 4th one just Greys out... 4090 7950x3d

[SnugglyGirl]

You may be over the limit for resolution.

Do a test and see if all the monitors will work set to 1440p.

On the 4090 specs it states this.

 

- Multi Monitor:

• 4 independent displays at 4K 120Hz using DP or HDMI
• 2 independent displays at 4K 240Hz or 8K 60Hz with DSC using DP or HDMI
• Other display configurations may be possible based on available bandwidth

[Kisai]

 

13 hours ago, Sporkyzz said:

Anyone have a clue why i can only get 3 monitors to work? When i click the 4th one just Greys out... 4090 7950x3d

It probably just doesn't have enough video bandwidth, but that again, depends on what you're using.

 

If you have connected all the devices with DP cables, directly to the dGPU, it should be fine.

If you've connected any of them with HDMI and have mistakenly connected one to the iGPU on the motherboard, then you're in generally unsupported territory. If you've connected a "display link" hub, (marketed as a way to plug in additional monitors) they are software-controlled GPU logic, so they have limits as well.

 

Generally, you should be able to connect as many monitors as the GPU has video bandwidth. So if you have 4, 4K monitors, that is 3840x2160x4x4x60 *8= 64gbits of bandwidth. Any combination of resolutions and refresh rates can't exceed what is defined as the maximum.

https://www.nvidia.com/en-us/geforce/graphics-cards/40-series/rtx-4090/

Quote

Display Support:	Maximum Resolution & Refresh Rate (1)	4K at 240Hz or 8K at 60Hz with DSC, HDR
	Standard Display Connectors	HDMI(2), 3x DisplayPort(3)
	Multi Monitor	up to 4(4)
	HDCP	2.3

 

So the important part is looking at (4) there which the previous poster quoted:

Quote

4 - Multi Monitor:

• 4 independent displays at 4K 120Hz using DP or HDMI
• 2 independent displays at 4K 240Hz or 8K 60Hz with DSC using DP or HDMI
• Other display configurations may be possible based on available bandwidth

So using back-of-the-envelope math, basically it's double the number I used above assuming SDR not HDR.

4(monitors) x 3840(h) x 2160(v) x 4(Bpp) x 120(hz) *8(bits)= 128gbits

 

So any combination of monitor configuration can't exceed 128gbits.

 

If you have 4, 4K monitors, therefor NONE of them can run above 120hz if you want it to work. If they're all 60hz, then there really shouldn't be a problem. If they run at 144hz, then that's a little too high. Likewise if you have something somewhere in between 1080p and 2160p like a 1440p display, then it's not quite using all the bandwidth a 4K would support, but not guarantee to work at 144hz either.

 

It's complicated. This might be more useful. Just add up each monitor. https://www.murideo.com/hdmi-21-bandwidth-calculator.html and if the combination of all 4 exceeds 128gbits, that's your problem. 

 

Another possibility, is simply that the HDMI or DP cables are not of the right type and the GPU is just signaling that this would overload the GPU.

 

It IS possible to use the iGPU on CPU's that have it in combination with dGPU's, however generally this is only a supported configuration on laptops. Desktops it's a bit of a crapshoot if the iGPU will work as intended. If you can, you should try to use the dGPU's ports as long as you haven't run out of bandwidth and only resort to the iGPU's ports as a last resort.

[Sporkyzz]

Okay so i have a g9 neo 240hz, 2 1080p 60hz monitors and one 27" 2560x1440 3 is connected to dp and one to hdmi.