using a 27" 2009 iMac as second display for 2017 MacBook Pro

Hey, joecab.

Thank you for getting back to us. Going by the models of the Macs you'll be using, the information is below.

Use your iMac as a display with Target Display Mode

System Requirements

You need the following to use Target Display Mode:

• A Mac notebook or desktop with a Mini DisplayPort or Thunderbolt port. If your Mac has Thunderbolt 3 (USB-C) ports, you can connect it using the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter.
• A Thunderbolt cable or a Mini DisplayPort to Mini DisplayPort cable
• A supported iMac with OS X v10.6.1 or later

See the list below for iMac models that support Target Display Mode, the type of cable you need to connect that model of iMac, and the kind of port you need on your other Mac.

iMac models you can use as a display	Cable you need	Port you need on your other Mac
iMac (27-inch, Late 2009)	Mini DisplayPort to Mini DisplayPort	Mini DisplayPort or Thunderbolt
iMac (27-inch, Mid 2010)	Mini DisplayPort to Mini DisplayPort	Mini DisplayPort or Thunderbolt
iMac (Mid 2011-Mid 2014)	Thunderbolt	Thunderbolt

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple

You'll plug that into the new MacBook Pro, then use a Thunderbolt/Mini Display cable to go from the Thunderbolt 3 to Thunderbolt 2 adapter into the MiniDisplay port on the iMac.

Cheers!

Hey, joecab.

I see that you have a late 2009 27" iMac and would like to use it as a second display with your 2017 MacBook Pro. I'm happy to provide the information you need.

Use your iMac as a display with Target Display Mode

Target Display Mode lets you use the built-in display on a supported iMac as an external display for another Mac.

Enjoy your day!

How about using this iMac as a display with the 2017 MacBook?