Weird issue/Laptop faster when connected to external monitor

Hi all, this is something I wanted to post long time ago. I have a Dell XPS laptop with thunderbolt 4 ports. When using the laptop connected to an external 4K monitor (via a thunderbolt cable and with the laptop's display disabled) the laptop feels snappier, everything I do within Windows feels faster compared with doing the same task with the laptop on its own (not connected to external monitor and laptop's display enabled). It seems as if the external monitor would do some processing saving some of the laptop's CPU/GPU usage. Thanks for any feedback on this mystery.

The refresh rates are probably different on the two displays. Laptop panels aren't known for speed.

You should compare (using a real benchmark program, instead of "feel"):
- Speed on the internal display
- Speed on HDMI/DisplayPort (whatever is not Thunderbolt)
- Speed on Thunderbolt
- Does it slow down when you have both displays open?

garlin said:

The refresh rates are probably different on the two displays. Laptop panels aren't known for speed

I checked the specs and both the laptop's display and the external monitor display refresh rates are equal (60Hz). Plus, you may notice a difference in refresh rates when gaming, but simple tasks as opening Excel, Notepad, browsing, etc shouldn't be noticeable

garlin said:

Does it slow down when you have both displays open?

No, with both displays enabled (internal+external) it's snappier as when only the external is enabled. It only feels slower when using the laptop's internal display alone.

Not talking about display refresh, it is regarding how the external display is able to interpret the data it receives to show it quicker than the display onboard the laptop.

bro67 said:

Not talking about display refresh, it is regarding how the external display is able to interpret the data it receives to show it quicker than the display onboard the laptop.

Yes, I thought about that too, maybe the interface between the motherboard and the internal display has a bandwidth much lower than that of thunderbolt 4 used to connect to the external display. If so, it'd be a shame for Dell to use cheap components creating bottlenecks in such expensive laptop.

Cost is not the only driver. There are pricey AlienWare and other gaming laptops with 144 MHz displays.

For a consumer laptop, battery life is a major review score. As Apple knows well, if you unleash the full transfer rate -- power consumption goes thru the roof. With an external display, you know that's not a factor. A laptop is expected to work with battery power only.

I use my laptop always AC powered even when using internal display, very seldom do I use it unplugged. Of course the whole point of a laptop is being mobile, but at least they should include a faster display interface and give the choice of power saving using Power Options in Windows so to include both usage scenarios (AC vs battery). As a side note, the performance difference is not huge, but it's noticeable enough to make external monitor use more enjoyable.

antares said:

Hi all, this is something I wanted to post long time ago. I have a Dell XPS laptop with thunderbolt 4 ports. When using the laptop connected to an external 4K monitor (via a thunderbolt cable and with the laptop's display disabled) the laptop feels snappier, everything I do within Windows feels faster compared with doing the same task with the laptop on its own (not connected to external monitor and laptop's display enabled). It seems as if the external monitor would do some processing saving some of the laptop's CPU/GPU usage. Thanks for any feedback on this mystery.

I wanted to share a very similar experience. I have a Dell XPS 9520. When connected to my external monitor (27inch, 4k, 60hz refresh rate) the laptop feels much snapier than when using the laptop screen (the laptop is always plugged in). This doesn't happen with my work laptop (HP Zbook firefly G9).

The Graphics lane is probably different. For instance you could run your labtop via external GPU and see a difference. If you have the external display plugged in, the computer will see it as the first adapter to boot from and take higher priority. It is no different with a VGA. Could simply be the order of which comes first and bus-lane speed. Sometimes you have special lanes for specific bus that is dedicated.

Labtops are just computers down to their minimum and greatest quality is the portability.

Nope, it's not that. The dedicated graphics card is always disabled. I can only assume that for some reason the input lag is greater when the laptop is not connected to an external monitor. I note that I also use the external monitor as hub for my mouse and keyboard.