Well, Im a programmer and I want bunch of monitors.

I have a 21.5 Inch 5K iMac, from 2017

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Just bought a DUAL HDMI Adapter from StarTech.com

My intention is to have 3 extra displays because the Mac has 2 thunderbolt 3 ports so in 1 port I connected the StarTech adapter and in the other one a simple Thunderbolt 3 to HDMI adapter

But when they are connected together I have 2 random displays working, I cant get the 3 extra display to work!

In the past I have both thunderbolt ports with the single HDMI adapter and worked fine.

Im afraid that this iMac, due its 4K resolution, can't handle 3 extra monitors.

What do you say? Thanks.

1 Answer 1


Apple documents the supported displays now from the installed OS:

Check how many displays your Mac supports: Choose Apple () menu > About This Mac > Support, then click Specifications. On the web page that appears, the number of displays your Mac supports appears under Video Support.

I don’t recommend using more than the official, but sometimes people are OK with adapters that split up a display if they don’t care about full resolution or refresh rates as much as maxing out the total square inches of display.

Another option is using an external GPU. See Use an external graphics processor with your Mac on Apple's website.

From your comments you should expect three 4k displays - up to 2 4K external displays and the iMac integrated one.

  • Great link on the eGPU - thunderbolt 3 is USB 4 is fast and hugely extensible for graphical expansion.
    – bmike
    Commented Oct 23, 2019 at 23:46
  • Wow really helpful information, my Mac specs tell that can handle up to 2 4K external display. Im using 2 FULL HD ones so I wonder if there's something I can do to change that. Commented Oct 23, 2019 at 23:52
  • 3 distinct 4K displays is a graphic beast. I love the LG 4K displays for text / programming @KarloA.López There are less expensive ones, Dell has some decent ones as well. Go vertical if you can side by side.
    – bmike
    Commented Oct 24, 2019 at 0:05

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