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I’m purchasing a 2017 MacBook Pro and plan to use my old Mid-2011 iMac as a monitor in Target Display Mode.

I’ve discovered I need a USB-C to Thunderbolt 2 connection to make this work, but I’m having some difficulty finding a cable that works. I tried a USB-C to Mini-Display Port (using my work laptop, same as I’m ordering) without success.

Does such a cable exist?

I’ve seen male USB-C to female Thunderbolt 2 adapters that would require a male to male Thunderbolt cable, but they’re pricey and I’d like some confirmation that they work before I purchase one.

Can anyone confirm that this setup would work please?

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  • James, did you ever solve this problem? I have the exact same issue: Mid-11 iMac, and 2017 MB Pro... and indeed, that Thunderbolt 3 -> Thunderbolt 2 adapter is pretty expensive (here in Belgium: €55 = $62, plus the regular Thunderbolt 2 cable at €35 = $40). $100 Just to connect your (slower..) iMac to your faster MB-Pro... If it works, ok... I was also looking for a single cable, but that doesn't seem to exist.
    – HansM
    Commented Mar 14, 2019 at 20:40

2 Answers 2

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You're not going to find a Thunderbolt 3 to Thunderbolt 2 cable as an adapter is required to connect to legacy devices.

One of the (major) differentiators between Thunderbolt 1/2 and Thunderbolt 3 is that Thunderbolt 1/2 required the cable to be active (it required power to operate) whereas Thunderbolt 3 can use standard USB Type C cables (it's passive)1.

With these older Thunderbolt standards, the cable was active, meaning the cable itself is a device that requires power to operate (which is why most Thunderbolt 1 or 2 devices would require an external power source in order to function.)

Thunderbolt 3 is backward compatible, but will require an adapter.2

From the FAQ:

Is Thunderbolt 3 backwards compatible with Thunderbolt and Thunderbolt 2?

Yes, solutions and products built to Thunderbolt and Thunderbolt 2 specifications will work with Thunderbolt 3 via an adapter.

(emphasis mine)

To make your setup work, something like the StarTech TBT3TBTADAP TB 3 to Legacy TB adapter.

StarTech TBT3TBTADAP

I've personally used this adapter to connect a 2018 MacBook Pro to a legacy (Thunderbolt 1) WD MyBook Duo and it worked with no issues.

Note

This kind of adapter is only compatible with Thunderbolt devices, not Mini DisplayPort.

1 C|Net: USB Type-C and Thunderbolt 3: One port to connect them all

2 Thunderbolt Technology Frequently Asked Questions

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    I would recommend the Apple adapter from my answer instead as it is cheaper, and I have actually verified that it works with Target Display Mode!
    – jksoegaard
    Commented Nov 28, 2018 at 21:28
  • @jksoegaard - I tend to not recommend Apple branded adapters/dongles because they have a high tenancy to fail and the reviews on the Apple store seem to confirm my experiences.
    – Allan
    Commented Nov 28, 2018 at 21:36
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    Sounds like anecdotal evidence - my experience is the contrary. We have used many different types of Apple adapters/dongles in my company, and we've had very low failure rates. In particular, we haven't yet had a failed Thunderbolt 3 to Thunderbolt 2 adapter. Do you have any statistics to back up that Apple's hardware is subpar to StarTech?
    – jksoegaard
    Commented Nov 28, 2018 at 21:48
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    @jksoegaard as Allan said, the reviews on Apple adaptors are often rather low. I’d also like to point out that you dismissed his comment by saying it was anecdotal and proceeded to provide more anecdotal evidence. Do you have statistics?
    – Tim
    Commented Nov 29, 2018 at 0:03
  • @Tim I know it is anecdotal - that was the point. Two anecdotes that are conflicting - doesn't really help anyone. What is necessary is statistics in order to generally claim that Apple's adapters fails more often than other brands. If I had statistics, I would have posted them.
    – jksoegaard
    Commented Nov 29, 2018 at 8:38
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I don't think a straight-up cable exists, no. However, you can get an adapter/dongle that works perfectly well for your scenario. You'll need to Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter:

https://www.apple.com/us_smb_83039/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter

You can read more about the adapter here:

https://support.apple.com/en-gb/HT207266

Note that Target Display Mode is not using the same kind of signal as mini-DisplayPort - therefore a USB-C to mini-DisplayPort cable will not work! It needs to be an actual Thunderbolt 2 source.

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  • Re: signal for target display mode, it is either Thunderbolt or DisplayPort, depending on generation.
    – user71659
    Commented Nov 29, 2018 at 2:50
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    @user71659 Yes, but this question is about the mid-2011 iMac, which uses Thunderbolt - and not a mini-DisplayPort signal.
    – jksoegaard
    Commented Nov 29, 2018 at 8:39
  • just to validate what jksegaard said: to connect a 2017 Macbook Pro to a 2011 iMac, I recommend:
    – Antonio23249
    Commented Mar 2, 2019 at 5:28

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