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Ever since upgrading to a new PC and Windows 10 a few years back, I've experienced terrible lag (it's totally unusable, feels like 5 FPS) while trying to remote into the aforementioned desktop while the monitor is off.

This can be avoided if I use an HDMI cable alongside the DisplayPort cable going into the same monitor, but it's a very weird solution and I'd rather find a different fix.

I unfortunately need to use a DP cable to get the full specs out of my monitor, otherwise I would just opt to use HDMI only.

To my understanding, when the OS stops detecting a monitor (which seems to happen when you turn off a monitor that is connected via a DP cable), the GPU goes into a very low power-state. Is this something that can be changed within Windows?

I never experienced such issues on old hardware within Windows 7 and I've remoted into my old Windows 7 machine without a monitor many times in the past. This leads me to believe it's an issue within Windows 10 or modern hardware.

I've disable ULPS within the registry and I'm positive I've disabled every power saving setting within the BIOS.

I've seen comments on another website that suggest the use of a dummy HDMI plug or virtual display drivers, but again I'd rather an actual solution rather than an emulation workaround.

  • CPU: Ryzen 5 5600X
  • GPU: 6900 XT
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  • Just chiming in to add that this is indeed a thing: With my machine (no monitor connected at all, exclusive RDP usage), it happens when sent it into sleep/hibernate and then continuing work - laggy as hell. I also had to set the Windows Setting for Power Saving to "Ultimate" (basically turning it off AFAIU) to properly work via RDP. Maybe with such a plug as mentioned in the answer I could use sleep/hibernate again.
    – Martin
    Commented Apr 11 at 8:43

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You say:

“This can be avoided if I use an HDMI cable alongside the DisplayPort cable going into the same monitor, but it's a very weird solution and I'd rather find a different fix.”

Then you need to use what is called an HDMI “Dummy Plug” or “Headless 4K Display Emulator.”

I am not experienced with Windows, but I faced a problem with a similar slowness with RDP on a Mac mini running OS X and the issue was solved by using an “HDMI Dummy Plug.”

Basically it plugs into your machine’s HDMI port and tricks it into thinking an HDMI display is connected. Thus enabling remote sessions to be sped up because graphics are now being rendered by the GPU; instead of software rendering which is slow.

Why does this work? Not too sure!

I believe that for many systems the HDMI port needs to be active for the GPU to render graphics on an RDP connection. And this device works by tricking your system into believing that an HDMI monitor is connected to the system; thus RDP graphics are rendered via the GPU instead of software rendering which is CPU intensive and slow.

Here are two examples of this cheap and tiny devices with key descriptive text copied here for clarity:

  • Adafruit’s “HDMI Dummy Plug” (Product ID: 4247): “This HDMI Dummy Plug is a small device that acts as a display emulator. Once it's plugged into the video output socket on your device or computer, the plug punks the operating system into detecting a connected display, and voilà! Now you have unimpeded access to your graphics card hardware.”
  • OWC’s Newer Technology HDMI Headless 4K Display Emulator (SKU: NWTADP4KHEAD): “With the NewerTech HDMI Headless 4K Display Emulator, you can now break free of limited 1024 x 768 or 1280 x 1024 resolution headaches when accessing macOS, Windows, and Linux machines remotely while viewing the desktop with up to full 4K 4096 x 2160 resolution.”

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Bonus Update: Further research by me found out these “HDMI Dummy Plugs” can also be known as “EDID emulators”; more info below:

“EDID records the information of a display such as the dimensions/screen size, original resolution, color properties, frequency range limits, etc. EDID handshakes enable the information exchange and when the computer gets it, it will deliver the image that fits the display.”

And this:

“EDID emulator helps address communication issues between an HDMI video source and a display. By copying or ghosting an EDID, the emulator can relay information from the display to the computer.”

Note that while HDMI dummy plugs are relatively simple and cheap devices, EDID emulators are more complex and can do a few more cool tricks like trick systems into believing non-HDCP compliant displays are HDCP compliant.

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    I can confirm that we use this exact type of device for this exact reason in the test farms at work.
    – gilliduck
    Commented Apr 10 at 10:48
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    I use the cheap basic dummy plug for remote desktop software that 'needs' a live desktop - that they're that cheap is one of the few good things that came out of the bitcoin frenzy :D
    – Journeyman Geek ♦
    Commented Apr 11 at 2:39
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    An edid emulator is an entirely more complex and wonderful device that lets you do slightly naughty things- and rather pricier. The dummy plugs are rather simple devices - I used a emulator to outright lie about HDCP compliance and it was glorious. superuser.com/a/1777323/10165
    – Journeyman Geek ♦
    Commented Apr 12 at 4:19

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