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macrumors newbie
Original poster
Jun 15, 2018
Hi all,

I wonder if anyone can help. I've recently purchased a 2017 iMac Retina 4K (21.5 inch) and I'm looking for the easiest, cheapest way to add a second display.

Apologies if this question has been asked/answered before, but I can't seem to find a satisfactory answer anywhere.

In an ideal world, I'd have liked to have used my old iMac (21.5 inch Late 2013 iMac) as a second screen, but it seems there's no easy way to make this work (although if one of you can show me a way, I'd be your friend for life!).

Can anyone offer any advice?

Much appreciated.



macrumors member
Mar 31, 2016
Your iMac should support just about any display out there- you just might need a dongle or adapter cable. Video out should be over the Thunderbolt 3 (USB-C) ports, which means you’ll have the simplest time finding a cable that does USB-C to DisplayPort, and using that to connect to any external monitor that accepts DisplayPort. There are quite a few out there; I’ve had good experiences with some Dell options. Just do a bit of research on 21-24” 4K screens and see which one gets good reviews in your price range. :)

You’ll definitely need an adapter to connect to a display over HDMI, DVI, or VGA...if you’re buying new kit, save yourself the hassle and don’t bother going that route here.

As far as re-using your old iMac- They toyed with that exact feature on the first few years of the 27” models, but dropped it in 2012 and never supported it on the 21” model. If you don’t have a use for the machine, might consider selling it. Always a decent market for used iMacs in good condition.
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