Why are two displays faster than one display?

[Understandout]

Hey guys. I hope this will be an easy question for you.

The specs don't really matter. I have recently bought a 21 inch screen to use with my laptop (Win 8.1). The resolution of the external screen and of my laptop are the exact same, 1080p. I do not need my laptop screen and figured I won't suffer any performance loss if I go to the Screen Resolution page and choose "Show Desktop only on 2." This disables my laptop screen and only uses the external display.

So here's the weird part. When playing a game (The Witcher 3), it worked fine on my laptop, but it runs horribly on the external display. The framerate is lowered significantly (used Fraps). I can also confirm the in-game settings haven't changed and the resolution is lowered to 768p, as it should be.

After going back to the Screen Resolution settings and choosing duplicate screens (both screens show the same), the game runs fine on the external display. This does not make sense to me. Why would my performance be better when the laptop projects images to two screens instead of one screen?

I would like to save my laptop the trouble of using my laptop screen at all and only use my external screen.

 

[jaguarskx]

It sounds like a video driver issue. Try updating to the most current version drivers for your graphics card. If that does not fix the issue, then you may need to wait for another driver revision.

 

[Understandout]

I figured it out and the problem was very specific to my laptop. I had my lid closed when I disabled my laptop screen and I opened it when I duplicated the screens. Apparently my fans are blocked when the lid is closed, which is why the laptop automatically chooses to cap the performance and stop it from overheating. This had no impact when browsing or playing a simple game like League of Legends, but The Witcher 3 obviously requires full power.

Sorry if I wasted anyone's time!

 

[hang-the-9]

I figured it out and the problem was very specific to my laptop. I had my lid closed when I disabled my laptop screen and I opened it when I duplicated the screens. Apparently my fans are blocked when the lid is closed, which is why the laptop automatically chooses to cap the performance and stop it from overheating. This had no impact when browsing or playing a simple game like League of Legends, but The Witcher 3 obviously requires full power.

Sorry if I wasted anyone's time!

Glad you found the answer, I would have gone with a video card issue also, maybe running on the onboard vs the faster second video card, so your finding out it was just a heat issue may help others troubleshoot a similar issue.