I have just bought the new 24" iMac (M1) and tried to connect my old iMac 27" (2013) as an external monitor. My new iMac won't detect the external display. I am using a USB-C Display Port to Mini-Display Port cable (no adapters). Please help.
iMac (M1, 2021)
That's not going to work. Your 27" 2013 iMac does not support, and never supported, Mini DisplayPort input.
It does support Thunderbolt Target Display Mode – where you are sending video from another Thunderbolt-equipped Mac over a Thunderbolt connection, and you use a special key combination to tell the 2013 iMac to display the incoming video.
Use your iMac as a display with target display mode - Apple Support
Unfortunately, Apple added some restrictions to Thunderbolt Target Display Mode. The "other Mac" (in this case, the 24" M1 iMac) must have been introduced in 2019 or earlier, and have macOS Catalina or earlier installed. Your 24" M1 iMac is new enough to fail both tests.
So even if you connected the iMacs with a Thunderbolt 3-to-2 adapter ($50), and a Thunderbolt 1/2 cable ($30), you wouldn't be able to use your 27" 2013 iMac in the way you want.
That's not going to work. Your 27" 2013 iMac does not support, and never supported, Mini DisplayPort input.
It does support Thunderbolt Target Display Mode – where you are sending video from another Thunderbolt-equipped Mac over a Thunderbolt connection, and you use a special key combination to tell the 2013 iMac to display the incoming video.
Use your iMac as a display with target display mode - Apple Support
Unfortunately, Apple added some restrictions to Thunderbolt Target Display Mode. The "other Mac" (in this case, the 24" M1 iMac) must have been introduced in 2019 or earlier, and have macOS Catalina or earlier installed. Your 24" M1 iMac is new enough to fail both tests.
So even if you connected the iMacs with a Thunderbolt 3-to-2 adapter ($50), and a Thunderbolt 1/2 cable ($30), you wouldn't be able to use your 27" 2013 iMac in the way you want.
That worked perfectly!!! Thank you so much!!
New Macs do not support Target Display Mode. You cannot use a another iMac as a monitor.
Use your iMac as a display with target display mode - Apple Support
Target Display won't work. I posted the link so you could see why.
What does work fairly well is AirServer as I mentioned. :)
Here's a screen shot of a 2012 iMac used as an AirPlay Receiver.
FWIW, you could try the trial of AirServer to see if it meets your needs. You would install it on your 2013 iMac so it can act as an AirPlay receiver.
Thank you for your replies.
I didn't want to dispose of my old iMac and thought I could use it in some way. I will try the target display mode as suggested. Thanks again. :)
Thank you so much, I will try that :)
You're welcome.
Connecting old iMac to my new iMac, as a second display
