afshin6760 wrote on 2025-12-19, 08:32:

Hi , […]
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Hi ,

I’m planning a setup where I have a modern GPU (e.g., RTX 5050) for gaming, but want to use a CRT monitor via an older secondary GPU (e.g., Radeon R56) because DP→VGA adapters don’t give proper refresh rates above 60Hz.

I’m wondering:

1. Is this setup actually feasible?

2. Could it cause any bottleneck or conflict between the GPUs?

3. Does the modern GPU need to have a monitor connected for mirroring/output, or can the CRT run entirely on the old GPU independently?

Thanks for any insights!

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, I have never tried this but I think you'll run into some quirks if there is even a way to do it. If you think about it, a GPU is built to output to... well, it's outputs. Forcing the final rendered frame back through the PCI-E interface to another card, through it's GPU and to that GPU's outputs would not be desired behavior for a graphics card normally.

I think if there's a way to get the RTX card's output mirrored to the other card you'll run into issues with refresh rates and resolutions, among other things. Simply because the RTX card will not have a way to communicate with the other display (for EDID, vsync, etc.) since it is connected to a different card.

Anyway, I could be wrong about all this. Just wanted to put in my two cents. If you do get it working please post about your experiences here because this kind of setup isn't well documented online.

Ozzuneoj wrote on 2025-12-19, 11:19:

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, […]
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afshin6760 wrote on 2025-12-19, 08:32:

Hi , […]
Show full quote

Hi ,

I’m planning a setup where I have a modern GPU (e.g., RTX 5050) for gaming, but want to use a CRT monitor via an older secondary GPU (e.g., Radeon R56) because DP→VGA adapters don’t give proper refresh rates above 60Hz.

I’m wondering:

1. Is this setup actually feasible?

2. Could it cause any bottleneck or conflict between the GPUs?

3. Does the modern GPU need to have a monitor connected for mirroring/output, or can the CRT run entirely on the old GPU independently?

Thanks for any insights!

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, I have never tried this but I think you'll run into some quirks if there is even a way to do it. If you think about it, a GPU is built to output to... well, it's outputs. Forcing the final rendered frame back through the PCI-E interface to another card, through it's GPU and to that GPU's outputs would not be desired behavior for a graphics card normally.

I think if there's a way to get the RTX card's output mirrored to the other card you'll run into issues with refresh rates and resolutions, among other things. Simply because the RTX card will not have a way to communicate with the other display (for EDID, vsync, etc.) since it is connected to a different card.

Anyway, I could be wrong about all this. Just wanted to put in my two cents. If you do get it working please post about your experiences here because this kind of setup isn't well documented online.

On my old laptop, the NVIDIA 710M doesn’t actually output the display—Intel HD Graphics 2000 handles all the display tasks, both for the built-in screen and for a CRT, including EDID, refresh rate, resolution, and Vsync. I think the same thing should happen on a desktop setup using an older AMD GPU for the CRT while an RTX 5050 handles rendering.

I assume you want to do this, but on a motherboard with VGA output: https://www.youtube.com/watch?v=_rxFxdvO3fQ

A lot of people use this method and buy cheap(ish) compute AMD/Nvidia cards without any outputs to play games. I think it's a bit more complicated to pull on Windows with 2 discrete cards.

The Serpent Rider wrote on 2025-12-19, 12:43:

I assume you want to do this, but on a motherboard with VGA output: https://www.youtube.com/watch?v=_rxFxdvO3fQ

A lot of people use this method and buy cheap(ish) compute AMD/Nvidia cards without any outputs to play games. I think it's a bit more complicated to pull on Windows with 2 discrete cards.

Do you mean using the iGPU instead of a second old GPU for the CRT?

What resolutions are you targeting? There are HDMI to VGA adapters that can hit 120Hz at 640x480. There are also DP to VGA adapters that do support higher refresh rates as well. The problem is the DACs in them change all the time, so be prepared to buy and do returns if they don't work.

https://www.youtube.com/watch?v=U58nfvEklcs

SScorpio wrote on 2025-12-19, 13:36:

What resolutions are you targeting? There are HDMI to VGA adapters that can hit 120Hz at 640x480. There are also DP to VGA adapters that do support higher refresh rates as well. The problem is the DACs in them change all the time, so be prepared to buy and do returns if they don't work.

https://www.youtube.com/watch?v=U58nfvEklcs

At least in my country's (iran) market there are no good converters that give 1024 x 768 85hz

afshin6760 wrote on 2025-12-19, 12:32:

Ozzuneoj wrote on 2025-12-19, 11:19:

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, […]
Show full quote

afshin6760 wrote on 2025-12-19, 08:32:

Hi , […]
Show full quote

Hi ,

I’m planning a setup where I have a modern GPU (e.g., RTX 5050) for gaming, but want to use a CRT monitor via an older secondary GPU (e.g., Radeon R56) because DP→VGA adapters don’t give proper refresh rates above 60Hz.

I’m wondering:

1. Is this setup actually feasible?

2. Could it cause any bottleneck or conflict between the GPUs?

3. Does the modern GPU need to have a monitor connected for mirroring/output, or can the CRT run entirely on the old GPU independently?

Thanks for any insights!

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, I have never tried this but I think you'll run into some quirks if there is even a way to do it. If you think about it, a GPU is built to output to... well, it's outputs. Forcing the final rendered frame back through the PCI-E interface to another card, through it's GPU and to that GPU's outputs would not be desired behavior for a graphics card normally.

I think if there's a way to get the RTX card's output mirrored to the other card you'll run into issues with refresh rates and resolutions, among other things. Simply because the RTX card will not have a way to communicate with the other display (for EDID, vsync, etc.) since it is connected to a different card.

Anyway, I could be wrong about all this. Just wanted to put in my two cents. If you do get it working please post about your experiences here because this kind of setup isn't well documented online.

On my old laptop, the NVIDIA 710M doesn’t actually output the display—Intel HD Graphics 2000 handles all the display tasks, both for the built-in screen and for a CRT, including EDID, refresh rate, resolution, and Vsync. I think the same thing should happen on a desktop setup using an older AMD GPU for the CRT while an RTX 5050 handles rendering.

Yes, that's common on laptops because they are built with that configuration in mind but on desktops using two discrete GPUs the situation is very different.

afshin6760 wrote on 2025-12-19, 13:26:

Do you mean using the iGPU instead of a second old GPU for the CRT?

Yes.

The Serpent Rider wrote on 2025-12-19, 14:55:

afshin6760 wrote on 2025-12-19, 13:26:

Do you mean using the iGPU instead of a second old GPU for the CRT?

Yes.

It makes sense, but if the RTX 5050 can actually send the image to the IGPU (and not have the IGPU render the game) and not create a bottleneck?

Ozzuneoj wrote on 2025-12-19, 14:41:

afshin6760 wrote on 2025-12-19, 12:32:

Ozzuneoj wrote on 2025-12-19, 11:19:

If you are talking about having the RTX 5050 do the game rendering and having the end result output through the Radeon to a CRT, I have never tried this but I think you'll run into some quirks if there is even a way to do it. If you think about it, a GPU is built to output to... well, it's outputs. Forcing the final rendered frame back through the PCI-E interface to another card, through it's GPU and to that GPU's outputs would not be desired behavior for a graphics card normally.

I think if there's a way to get the RTX card's output mirrored to the other card you'll run into issues with refresh rates and resolutions, among other things. Simply because the RTX card will not have a way to communicate with the other display (for EDID, vsync, etc.) since it is connected to a different card.

Anyway, I could be wrong about all this. Just wanted to put in my two cents. If you do get it working please post about your experiences here because this kind of setup isn't well documented online.

On my old laptop, the NVIDIA 710M doesn’t actually output the display—Intel HD Graphics 2000 handles all the display tasks, both for the built-in screen and for a CRT, including EDID, refresh rate, resolution, and Vsync. I think the same thing should happen on a desktop setup using an older AMD GPU for the CRT while an RTX 5050 handles rendering.

Yes, that's common on laptops because they are built with that configuration in mind but on desktops using two discrete GPUs the situation is very different.

how about rtx 5050 and igpu ? (If the crt vga is connected to the motherboard) (and not using igpu to render the game )

afshin6760 wrote on 2025-12-19, 15:27:

It makes sense, but if the RTX 5050 can actually send the image to the IGPU (and not have the IGPU render the game) and not create a bottleneck?

I'm pretty sure none of the garden variety CRTs can exceed double data link DVI limit, which is about 8 Gbps. Even if you place RTX 5050 into a PCIe 3.0 slot, that's still about 60Gbps. And if you use a non-gimped RTX card with full 16x lanes, that's 120Gbps.

You didn't mention platform but this scenario of rendering on one GPU and outputting to displays connected to a different GPU is possible on Linux using PRIME, named after the option in the Nvidia drivers and originally introduced by them, and has since been implemented in the open source driver (mainly usable on Intel and AMD). See the Arch Linux wiki for details.

The framebuffer is transferred from the GPU that did the rendering to the GPU with the displays connected to it (i.e. performing the scanout). There is a minor performance impact since some PCIe bandwidth is used for that; for 1024x768x32 85Hz this is 255MiB/s or about as much as PCIe 1.0x1. I haven't tried this before though, I use only iGPUs on desktops.

jtchip wrote on 2025-12-20, 02:38:

You didn't mention platform but this scenario of rendering on one GPU and outputting to displays connected to a different GPU is possible on Linux using PRIME, named after the option in the Nvidia drivers and originally introduced by them, and has since been implemented in the open source driver (mainly usable on Intel and AMD). See the Arch Linux wiki for details.

The framebuffer is transferred from the GPU that did the rendering to the GPU with the displays connected to it (i.e. performing the scanout). There is a minor performance impact since some PCIe bandwidth is used for that; for 1024x768x32 85Hz this is 255MiB/s or about as much as PCIe 1.0x1. I haven't tried this before though, I use only iGPUs on desktops.

That makes sense, thanks for the detailed bandwidth breakdown — 255 MB/s is surprisingly low.
I’m staying on Windows (10/11), which already allows selecting GPUs per app via the Graphics Settings (high performance vs power saving), so this still seems viable.
Based on this, using an old AMD card purely for VGA/CRT scan-out shouldn’t be a bottleneck.

All laptops since gpus were ever added do this.

I believe that due to the immense number of people who plugged into their mobo and called support complaining of performance, the "branch" of the driver that enabled that was made standard at a modest performance cost.

So... It might "just work".

All it really is is copying the framebuffer from one card to another.

If it does just work, buy the next dumbass you see a beer.
They do important work.

myne wrote on 2025-12-20, 12:03:

All laptops since gpus were ever added do this. […]
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All laptops since gpus were ever added do this.

I believe that due to the immense number of people who plugged into their mobo and called support complaining of performance, the "branch" of the driver that enabled that was made standard at a modest performance cost.

So... It might "just work".

All it really is is copying the framebuffer from one card to another.

If it does just work, buy the next dumbass you see a beer.
They do important work.

so I don't know it's better use old gddr3 amd gpu or igpu

Try igpu if you have it first.

myne wrote on 2025-12-20, 14:01:

Try igpu if you have it first.

I don't have it im planning to buy a pc parts . i only have laptop now

After a little research, I found out that using this method with an iGPU is much more risky because many motherboards do not allow the simultaneous use of an iGPU and graphics.
i guess i should get b560 plus + 10400f/10100f + secondary gddr3 amd gpu with vga output

myne wrote on 2025-12-20, 12:03:

All laptops since gpus were ever added do this.

Not necessarily, the earlier ones used a mux to switch the display outputs between the integrated and discrete GPUs. AIUI those made in the last 10-15 years, perhaps when PCIe bandwidth became sufficient so as to not cause a significant performance dip, switched to mux-less designs.

myne wrote on 2025-12-20, 12:03:

All it really is is copying the framebuffer from one card to another.

Indeed but it needs the drivers to have ability to do that. Easier to do that on a laptop with a fixed configuration and laptop vendor-supplied drivers but a potential nightmare on a desktop with any combination of devices and drivers.

In a sense this is a special case of ATI Crossfire where instead of sharing the rendering between 2 GPUs (one of which can even be integrated in the case of Hybrid Crossfire), one GPU does all of the rendering work.

afshin6760 wrote on 2025-12-20, 19:03:

After a little research, I found out that using this method with an iGPU is much more risky because many motherboards do not allow the simultaneous use of an iGPU and graphics.

It depends on the motherboard. Don't know about Windows but on Linux this combination has some use because the dGPU is disabled, and hence draws no power, when not in use and iGPUs have lower power draw at idle or light loads.

In any case, this thread really belongs on Milliways since an old secondary GPU that can do this really isn't that old. You should ask on other forums too.