Is it possible to connect 3 external displays (for a total of 4, including the built-in 5K display) to an iMac Retina 5K, 27-inch, 2017? I have the Radeon Pro 580 with 8GB of VRAM.

I do not need the external displays to be high resolution. In fact, all three of them need to connect via VGA using the following resolutions:

  • External displays 1 & 2: 1920x1080
  • External display 3: 1280x720

If necessary the 3rd display could be a different connection type (e.g. DVI) and/or resolution. The specs for external displays 1 & 2 are not negotiable.

I've reviewed this iMac's specs which seem to say only 2 external displays are supported via the two ThunderBolt 3 (USB-C) ports. However in my research about ThunderBolt it seems like it should be possible to run two simple displays off of one port.

  • Sorry to trouble but could you please let me know if you went with the Diamond USB Adapter? There is so much talk about needing Thunderbolt to add more than 1 external monitor. Now, I'm low on the food chain of Apple knowledge, and I bet that I could (and for just $51 might) add a 4th monitor with that product.
    – rather
    Commented Jul 28, 2017 at 1:42
  • btw: With so much screen real estate, I can't function without 2 magic trackpads. And, there is a way to assign the monitor into which each app opens its files. anyway, sorry to trouble.
    – rather
    Commented Jul 28, 2017 at 1:45
  • I have not tried your solution yet but I may end up doing so. I have some hoops to jump through on my end first so it will be a while before I can post back. Commented Jul 28, 2017 at 17:55

1 Answer 1


I have attached 3 external displays to my MacBook circa late 2011. I stumbled across this nifty product:
Diamond USB Multi-Display Adapter

1 monitor is via the MiniDisplay port and 2 are attached to a USB hub (at USB 2.0 speed).

However, on some forum (that I can't even find anymore) someone mentioned this could possibly cause my CPU to overheat. I have used this 3 monitor config for a few days with no problems and I just started monitoring CPU temp.

I suspect that the performance on those USB monitors is awful? I've no idea. I know so little about graphics, I don't even know how to test them for performance...

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