Can an old display cause a MBP to run slow and pinball?

I have been using an Apple Cinema Display since I bought it new in 2010. It’s currently attached to a 2018 MacBook Pro running Mojave.

The MBP would often beachball when I had too many Safari tabs open. When I ran Activity Monitor, I saw kernel_task and WindowServer using a lot of system resources.

Last night I remembered reading an article that said WindowServer can slow your system down if you’re running an external display. And I thought, “I don’t think I have this problem when the MBP is running disconnected.”

So I disconnected the Cinema Display and all morning the MBP has been zooming along.

Could the Cinema Display indeed be the cause of the problem or is my newly speeded up Mac a coincidence? And is there a fix other than buying a new display?

I have the MBP connected to the Cinema Display using this USB-C to Mini Display Port adapter. Maybe the adapter is the problem?

P.S. I’m actually not particularly dissatisfied just working in the 13" MBP display with no external monitor attached.

I think it’s probably that’s a factor.
When I was researching for my MBP purchase I was trying to establish if it was worth having a dedicated video card or not. I read something similar to what you have by the sounds of it. When there are more pixels to push it hits the performance, having a dedicated graphics card is supposed to take that work load.

The 13"s only have the integrated intel graphics don’t they rather than the dedicated Radeon Graphics? (Or did they do some 13’s with that option??)

You could try setting the display to a lower resolution and see if that helps? I believe another option is to get a dedicated graphics card housed in an external case (eGPU I think they call them).

I seem to recall hearing that an eGPU is expensive.

@stu_w, you’ve given me some excellent suggestions. The support page you referenced says the MBP13 2018 will indeed support one or two external displays at much higher resolution than this ancient Apple Cinema display can deliver.

However, you’ve planted an idea: Previously, I ran the MBP with the external display attached and the notebook open. I never use the notebook display and the external display together, so I closed the notebook and we’ll see if that works better.

Even as old as it is, the Cinema Display is more comfortable than the built-in notebook display when I’m working at my desk.

I do want to replace this old thing – but I’ve promised myself I won’t do it until I organize my office. And that’s going to take a while!

I suspect this old Apple Display is just plain worn out (to use a technical electrical engineering term) and requires an excessive amount of compute and/or memory to run. Either that or the adapter is the problem.

I welcome other insights on this!

I can’t imagine that a single external (non-4K/5K) external display would cause any modern Mac any difficulty at all. Maybe something weird is going on with the electronics of the (oldish) display that’s causing issues for the Mac, but even that is kind of hard to fathom. In no way is this stressing the GPU capability of your computer though.

That’s what I’m thinking.

I reconnected the old display – because the big screen is more comfortable, even if the resolution is nowhere near as good as a modern display – and it seems to be running fine.

But I haven’t been putting it to heavy use either. We’ll see how it goes in a couple of days.