Mac Pro and monitor options

Does anyone know … If I were to buy a new Mac Pro, could I connect my old (working) 27" 5K iMac to use it as a monitor? If so, how would that work? What cable connections would work? (My 2015 iMac only has Thunderbolt 2 ports) I assume I would have to power up the iMac, even to just use it as a monitor, right? So, that wouldn’t be very energy efficient, but with the cost of new 5K monitors … wow!
Please advise if this is feasible! Thanks!

I have a 2015 retina 27" iMac. Afaik it cannot be used as a monitor.

You might possibly be able to find a hardware techie who could modify it internally to do so, but thats not for the faint hearted. Its a shame, because it is a beautiful screen.

Or run Teamviewer or something similar on it and the new Mac Pro to use its screen remotely? (Not supported by SU though).

Might be better to sell it and buy a new monitor.

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I don’t have an iMac to test this on, but it looks possible:

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That’s very good to know - I hope to try it with my MacBook pro in a day or two, and will report back if/how it works.

The original instructions with the iMac said it wasn’t possible (then - late 2015).

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Thanks for the tip/lead Colin …
I will look into it!

Thanks John,
Please do report back on what you discover …
It would be such a waste to walk away from such a nice 27” 5K scene!

I see it needs a cable I haven’t got - Thunderbolt 3 (USB-C) to mini Display Port or Thunderbolt 2 cable. Apple do one, but for nearly £50. Will see if there’s a cheaper version on Amazon or eBay.

Amazon UK does this one for a more affordable £16 or so:

And that by the looks of it also needs a male to male Thunderbolt 2 or miniDisplayPort cable.

Which I can’t find (yet).

Or maybe there’s a single cable that will do it, USB-C to Mini Display Port?

Thought I found one on Amazon, but it says max display resolution is 4K, and my iMac is 5K. But maybe the best the MacBook can do is only 4K?

I have to go to a nearly local Apple Store this coming week but not until Thursday at earliest, so it may take a while to find the right cable at an affordable price. Looks as if the cable type and spec may be crucial.

Still willing to try this, but it will take a while to find a suitable cable with the right specs. Hopefully, before Christmas, but probably longer than my initial hope of a couple of days.


Looking further down the Apple support page I find, disappointingly:
iMac (Retina 5K, 27-inch, Late 2014) and later iMac models can’t be used as Target Display Mode displays.

So it looks as if it won’t work on a Late 2015 iMac. What a pity!

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I love Apple products, but they have a sometimes (evil?) tendency to restrict the futrue use flexibility beyond their products and intended use. And, of course, they are overly expensive!
Good Luck, we have the same year iMac, so keep me posted if you discover anything!
Thanks, Bill

Hey Colin,
You link informs me that: "iMac (Retina 5K, 27-inch, Late 2014) and later iMac models can’t be used as Target Display Mode displays".
This is a drag, because my iMac is a late 2015 model, and thus not workable!
I wonder WHY Apple feels compelled to limit the future use flexibility this way?
Very frustrating!
Thanks for trying to help!

That does seem odd. I’ll search more…

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They also have an annoying tendency to keep working well for many years beyond most of the competition, and retain some of the highest resale value in the industry. Go figure.

Anyway. What other manufacturer makes an all in one that you can use as a monitor beyond its intended use? Just curious which one is not evil.

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Yes monospaced,
Maybe “evil” is a bit too strong a word … like I said, I love Apple products, and have been a faithful consumer for many years. I’m just a bit frustrated that I can’t future convert this (perfectly good, but somewhat outdated) iMac in any way …
It’s a beautiful machine, but allows no upgrading beyond RAM additions (which I have done). I can’t reuse the monitor, or upgrade the CPU or the GPU, or easily install an SSD hard drive.
Apple’s message is: Buy a new one! (don’t upgrade, because our design has prevented that!)
Bit of a love/hate thing I guess … but, in balance, mostly love …

Thanks Colin,
Yes, you may have some search capabilities beyond us mere mortals … I’m hoping!

Who makes an all in one that allows you to make CPU and GPU upgrades? Also, if you haven’t noticed, most competing laptops are also locking down the upgrades. It’s necessary to get chassis small and where people want them. I really am curious. Which competing all in one with a 5k display (trick question, doesn’t exist) allows you to use it as a monitor after the computer is obsolete? Is there one or do you just want to focus on Apple being not as modular as a build it yourself box?

Thanks monospaced,
Actually Apple does make a platform that is much closer to a “modular build it yourself box”. It’s called the Mac Pro, and you can actually open it up and make upgrades and modifications. Bloody expensive, but its there …

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Yes, of course they do. But we’re talking about an iMac here.

The Mac Pro is expensive, but it would be far more expensive (and nearly impossible) to try to build a TRULY comparable PC. Several have tried, and got close, but they can’t match the expandability and finish at the price. And if you do go ahead and try to build a comparable from a Dell or HP, it is even more expensive than the Mac Pro, believe it or not.

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The MacPro specs are lackluster. A similar PC with a bigger SSD would cost much less (add a 200€ video card, GeForce GTX 780, for instance) to beat the Radeon in the Mac) Sorry for the Finnish in my examples:

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Well monospaced,
That makes me feel a little bit better about even considering purchasing a Mac Pro …
I took the liberty of looking up your profile and I see that you are running a Mac OS … what specifically is your machine?
Now that Apple is embarking on their own new M1 chip sets … prudence suggests that I wait to see what they produce in the next generation(s) of iMac’s and Mac Pro’s before I buy (of course this process will probably take years!). Or, maybe the “old” design Mac Pro’s will go on sale when there is something new? Do they ever do that?

Thanks Anssi,
Yes, it seems that the Mac Pro spec’s haven’t been updated to keep pace in a while.
And yes, there are very likely comparable and less expensive alternatives found in Windows machines.
But they are Windows machines. Part of the reason some of us are so fond of Apple machines is the Mac OS, not just the (beautiful) hardware.

I just responded to monospaced’s claim that the MacPro is so powerful that it is impossible to build a comparable Windows PC. I picked a comparable “workstation” from a local vendor and showed that it costs about half what the Mac Pro does. And my own “gaming” computer that cost about 1500€ outperforms those both, judging by benchmarks. Going through what the local vendor has to offer “out of the box” it seems to me that the fastest available computer is an about 4800€ “gaming” box (i9, RTX3080, etc.)

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