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Target Display Mode Assistance Required Please

K

Karlos879

macrumors newbie
Original poster
Dec 23, 2025
7
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I am attempting to set up target display with my iMac, but I'm having all sorts of trouble doing it....and I'm in need of some assistance...

My setup:

Master - 27" Late 2012 iMac Model ID 13,2 running High Sierra 10.13.6

2nd display - 27" Mid 2010 iMac Model ID 11,3 running El Capitan 10.11.6

I have both a Thunderbolt 2 cable and a DisplayPort cable, but neither will work for me.

I would love some help here please if anyone knows what I'm doing wrong?! Thanks.
 
hg.wells said:
Looks like you’re need a USB adapter for mini-display port for the 2nd iMac as your 2012 iMac doesn’t have a mini display port.

Adapters for the Thunderbolt or USB-C port on your Mac - Apple Support

Learn about different adapters for the Thunderbolt 5, Thunderbolt 4, Thunderbolt 3, or USB-C port on your Mac.
support.apple.com support.apple.com
Click to expand...
Sorry, but this is just incorrect.

2012 iMac has Thunderbolt 2, which works natively as mini DisplayPort.


A Thunderbolt cable will not work, because the 2010 iMac does not have Thunderbolt. You will need to use a Mini DisplayPort to Mini DisplayPort cable. In theory using adapters between mini DisplayPort and full size DisplayPort may work, but to play it safe, get a cable that is mDP on both ends. Also note that some DisplayPort cables are directional. If it doesn't work in one way, switch which end is plugged in to which computer.

Turn on both systems, and log in to the OS on both systems. Make sure a keyboard is connected to both systems.

Press Command-F2 on the 2010 iMac. Depending on your keyboard, you may have to hold Fn while pressing Command-F2. It takes a couple seconds to switch.

I used Target Display Mode daily between my 2010 iMac and my 2012 Retina MacBook Pro for many years, while the iMac was acting as "home server" as well as extra display.
 
Anonymous Freak said:
Sorry, but this is just incorrect.

2012 iMac has Thunderbolt 2, which works natively as mini DisplayPort.


A Thunderbolt cable will not work, because the 2010 iMac does not have Thunderbolt. You will need to use a Mini DisplayPort to Mini DisplayPort cable. In theory using adapters between mini DisplayPort and full size DisplayPort may work, but to play it safe, get a cable that is mDP on both ends. Also note that some DisplayPort cables are directional. If it doesn't work in one way, switch which end is plugged in to which computer.

Turn on both systems, and log in to the OS on both systems. Make sure a keyboard is connected to both systems.

Press Command-F2 on the 2010 iMac. Depending on your keyboard, you may have to hold Fn while pressing Command-F2. It takes a couple seconds to switch.

I used Target Display Mode daily between my 2010 iMac and my 2012 Retina MacBook Pro for many years, while the iMac was acting as "home server" as well as extra display.
Click to expand...
Thanks for the extra possible ways to get this to work....!
I am using a Mini DisplayPort to Mini DisplayPort cable (I had both types of cable). I have also tried reversing the cable.
I have tried Command-F2 on the 2010 iMac. I have also tried Fn while pressing Command-F2.
It still isn't switching.....
I'm about to throw the 2nd monitor through the window!
I really didn't think it was going to be this hard!
 
I really thought the Mini DisplayPort to Mini DisplayPort cable was going to work...
The 2010 iMac clearly shows a Mini Display Port on the rear, and the 2012 iMac has 2 Thunderbolt ports. It this the issue? Will a Mini Display Port cable work in a Thunderbolt port?

I've also just tried a 27" Late 2011 iMac running High Sierra with the 2012 iMac, and I can't seem to get that working with either cable either......
 
Last edited:
Karlos879 said:
I have tried Command-F2 on the 2010 iMac. I have also tried Fn while pressing Command-F2.
Click to expand...
I have had issues with activating Target Display Mode with keyboards (even Apple keyboards) that were not the one that came with the iMac. This happened with two different sets of Macs that I was trying to use for TDM at different times, one was a 2010 iMac as the target and the other was a 2011 as a target.

Once I got it working using a different keyboard, the 2010 connected just by plugging it in from then on.
 
Karlos879 said:
I really thought the Mini DisplayPort to Mini DisplayPort cable was going to work...
The 2010 iMac clearly shows a Mini Display Port on the rear, and the 2012 iMac has 2 Thunderbolt ports. It this the issue? Will a Mini Display Port cable work in a Thunderbolt port?

I've also just tried a 27" Late 2011 iMac running High Sierra with the 2012 iMac, and I can't seem to get that working with either cable either......
Click to expand...
A Mini DisplayPort cable will work on a Thunderbolt port as an output, but only for video. Since that's all you're trying to use it for, it should work. This will only work if one or both machines have "mini DisplayPort only" ports.

For connecting two Thunderbolt-equipped computers (the 2011 and 2012 iMacs to each other) Target Display Mode only works when using a Thunderbolt cable. If both ends are Thunderbolt, you can't use a mini DisplayPort cable.

Again note that some DisplayPort cables are "one way" - try swapping ends of the cable. (So the end you first tried on the "target" Mac is plugged into the "source" Mac, and the end you had plugged into the "source" Mac is on the "target.")

It's also just possible that something is wrong with your Target Mac! Just to verify, it is actually a 27" iMac and not a 21.5", correct? On the non-Thunderbolt models, only the 27" model (2560x1440 screen resolution) supports Target Display Mode. The 21.5" models do not. (Thunderbolt-equipped 21.5" models do support it; as long as they are not "Retina display.")
 
Anonymous Freak said:
A Mini DisplayPort cable will work on a Thunderbolt port as an output, but only for video. Since that's all you're trying to use it for, it should work. This will only work if one or both machines have "mini DisplayPort only" ports.

For connecting two Thunderbolt-equipped computers (the 2011 and 2012 iMacs to each other) Target Display Mode only works when using a Thunderbolt cable. If both ends are Thunderbolt, you can't use a mini DisplayPort cable.

Again note that some DisplayPort cables are "one way" - try swapping ends of the cable. (So the end you first tried on the "target" Mac is plugged into the "source" Mac, and the end you had plugged into the "source" Mac is on the "target.")

It's also just possible that something is wrong with your Target Mac! Just to verify, it is actually a 27" iMac and not a 21.5", correct? On the non-Thunderbolt models, only the 27" model (2560x1440 screen resolution) supports Target Display Mode. The 21.5" models do not. (Thunderbolt-equipped 21.5" models do support it; as long as they are not "Retina display.")
Click to expand...
Thank you for the response.....
Yes, all the machines I have tried are 27".
I have tried the following:
Master - 27" Late 2012 iMac Model ID 13,2 running High Sierra 10.13.6 which has 2 thunderbolt ports
2nd display - 27" Mid 2010 iMac Model ID 11,3 running El Capitan 10.11.6 which has a mini display port
I have both a Thunderbolt 2 cable and a DisplayPort cable, but neither will work for me, and I have tried swapping the ends of the cables too.

I have also tried:
Master - 27" Late 2012 iMac Model ID 13,2 running High Sierra 10.13.6 which has 2 thunderbolt ports
2nd display - 27" Late 2011 iMac running High Sierra with the 2012 which has 2 thunderbolt ports
This did not work either.....

All of the displays are 2560x1440 screen resolution...
It's still a no go......!
 
Karlos879 said:
Master - 27" Late 2012 iMac Model ID 13,2 running High Sierra 10.13.6 which has 2 thunderbolt ports
Click to expand...

Karlos879 said:
Master - 27" Late 2012 iMac Model ID 13,2 running High Sierra 10.13.6 which has 2 thunderbolt ports
Click to expand...
Are these both the same machine? Maybe something is up with your master, then.


Have you tried a different keyboard:
Juicy Box said:
I have had issues with activating Target Display Mode with keyboards (even Apple keyboards) that were not the one that came with the iMac. This happened with two different sets of Macs that I was trying to use for TDM at different times, one was a 2010 iMac as the target and the other was a 2011 as a target.

Once I got it working using a different keyboard, the 2010 connected just by plugging it in from then on.
Click to expand...


Another thing to try to eliminate potential sources of issues, try doing your Mid 2011 iMac as the source and your Mid 2010 as the target. You can also try any device that has DisplayPort out as the source, and your Mid 2010 iMac as the target. The 27" Late 2009 and 27" Mid 2010 will work with any device (Mac, PC, or anything) that has DisplayPort output.
 
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Alright, I got my 2010 iMac out of storage and gave it a shot.

Target Display: iMac (27-inch, mid 2010, 2.8 GHz Intel Core i5) only has miniDisplayPort, no Thunderbolt. Running macOS High Sierra, the latest that supports Target Display Mode as the "target" system.

Cable used†: https://www.amazon.com/dp/B08Q2TP25K (I couldn't find the old mDP-to-mDP cable I used to use with it back in the day.)

From: MacBook (Unibody Aluminum, 2008, 2.4 GHz Intel Core 2 Duo) - miniDisplayPort only, no Thunderbolt, using mDP-to-mDP cable above. Running OS X El Capitan:



From: MacBook Pro (15-inch Retina, Mid 2012, 2.6 GHz Intel Core i7) - Thunderbolt, using mDP-to-mDP cable above. Running macOS Catalina, the latest that supports Target Display Mode as the "source" system:


(This is the configuration I used for seven years, until I upgraded that MacBook Pro to a 2019, retired the iMac as "home server", and bought a second 4K display.)


†(The cable listing says "Not Compatible with iMac/Mac to MacBook" and "Not compatible with Target DisplayMode", because I'm sure they got a lot of people thinking they could use this on the Thunderbolt-equipped "Target" iMacs. It absolutely is compatible with Macs when going to a DisplayPort (not Thunderbolt) display, and when going to a non-Thunderbolt 27" 2009-2010 iMac for Target Display Mode.)
 
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Also, one nice thing about the DisplayPort Target Display Mode iMacs over the later Thunderbolt?

Because to the "source" Mac, it's just a DisplayPort monitor, not a Thunderbolt device, it works on the latest Macs.

Using a USB-C-to-mini-DisplayPort cable (note: every one of these I could find is unidirectional. If you get one that is "Mini DisplayPort to USB-C", it won't work,) I can use my 2010 iMac as a display for my work M4 Pro MacBook Pro running Tahoe.

 
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