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User profile for user: Aremis
Aremis Author
User level: Level 1
84 points

Using an older iMac as a second monitor for a newish iMac or Macbook Air?

Hey everyone


I have a question that I feel little confused by. Any guidance would be appreciated.


Situation: Just got a new job that uses an iMac for daily work.

iMac (Retina 4K, 21.5-inch, 2019)

Running MacOS Big Sur


Small screen means a real nuisance to work on. Company allows secondary monitors but won't supply them.


My question: Can I use an older iMac connected to the new one as a secondary monitor?


My existing home computer is:

iMac (27-inch, mid 2011)

Running El Capitan


The new mac has Thunderbolt 3

The old Mac has Thunderbolt 2.


Ive read a lot of stuff that hasn't been 100% clear.


Can I use a Thunderbolt 3 to Thunderbolt 2 adapter https://support.apple.com/en-gb/HT207266 on the new iMac, and using a thunderbolt 2 cable connected to the adapter on one end and the old iMac on the other, turn the old iMac into a secondary screen?


(I also mentioned Macbook Air in the title, because Im considering buying a new Macbook Air for personal use and would like to use it in the same manner)


Any input would be greatly appreciated.


Cheers!

iMac 27″, OS X 10.11

Posted on Jul 5, 2021 8:23 AM

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User profile for user: D.I. Johnson
D.I. Johnson
User level: Level 7
23,771 points

Posted on Jul 5, 2021 8:42 AM

You cannot do what you are considering. The new iMac must be running Catalina or earlier.


Here are the rules for Target Display mode on iMac:

click> Use your iMac as a display with target display mode - Apple Support


Target display mode is a feature that was available only with certain older iMac models.


Only the following older iMac models can be used as an external display when plugged into another older Mac model:

  • iMac models introduced in 2011, 2012, 2013, and mid 2014 using Thunderbolt or Thunderbolt 2 cable.
  • 24-inch and 27-inch iMac models introduced in 2009 and 2010 using Mini DisplayPort cable.
  • The intended target iMac must be running macOS 10.13 High Sierra or earlier; it does not work with macOS 10.14 Mojave or later, or with Boot Camp and Windows.*
  • Retina display iMacs won’t work as target displays.


  • In all cases the source Mac that you're connecting FROM must have been introduced in 2019 or earlier and have macOS 10.15 Catalina or earlier installed.
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User profile for user: D.I. Johnson
D.I. Johnson
User level: Level 7
23,771 points

Jul 5, 2021 8:42 AM in response to Aremis

You cannot do what you are considering. The new iMac must be running Catalina or earlier.


Here are the rules for Target Display mode on iMac:

click> Use your iMac as a display with target display mode - Apple Support


Target display mode is a feature that was available only with certain older iMac models.


Only the following older iMac models can be used as an external display when plugged into another older Mac model:

  • iMac models introduced in 2011, 2012, 2013, and mid 2014 using Thunderbolt or Thunderbolt 2 cable.
  • 24-inch and 27-inch iMac models introduced in 2009 and 2010 using Mini DisplayPort cable.
  • The intended target iMac must be running macOS 10.13 High Sierra or earlier; it does not work with macOS 10.14 Mojave or later, or with Boot Camp and Windows.*
  • Retina display iMacs won’t work as target displays.


  • In all cases the source Mac that you're connecting FROM must have been introduced in 2019 or earlier and have macOS 10.15 Catalina or earlier installed.
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Using an older iMac as a second monitor for a newish iMac or Macbook Air?

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