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iMac as second monitor to old one

Hi all,

I just bought the new 27" iMac, and my external monitor isn't compatible. I've talked with two different techs at Best Buy and both have told me the wrong cable, so I wanted to ask here. My old iMac is the 2010 model, with USB and firewire (I think that's what they're called) and I want to use it as the second monitor, but it doesn't have USB-C. What cable/adaptor, if any, would work? A thunderbolt cable doesn't because even though the techs said it had a USB end, it didn't. Any help would be much appreciated!

iMac 27″, macOS 11.5

Posted on Aug 8, 2021 9:52 AM

Reply
13 replies

Aug 8, 2021 11:11 AM in response to Writer26

Same link I provided and it clearly says:


To use any of these iMac models as an external display:

  • The iMac used as a display must have macOS High Sierra or earlier installed.
  • The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
  • The cable connecting the two Mac computers must be a Mini DisplayPort  cable.


Aug 8, 2021 10:27 AM in response to Writer26

Your 2010 iMac simply will not work as an external display. Please quit wasting your time. Target Display Mode is dead technology and Big Sur ( which is installed on the 2020) does not support Target Display Mode. Before you ask, no you cannot backdate the 2020 iMac to an earlier version of Mac OS.


In short, if your 2020 27" needs an external display you need to buy one. Please carefully read Target Display Mode (Target Display Mode).


We know this is not what you wanted to read but it is the truth, we your question multiple times per day and the answer is always the same.


By the way, you can find external displays that will work fine with the 2020 iMac for less than $100.

iMac as second monitor to old one

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