Charles Bewlay has a sad story:
My monitor that I use for my Mac mini got stolen in transit for repair. I’m wondering if I really need one since I have an iMac (that I can’t use as a monitor for it as it’s too old) and a 2015 MacBook Pro. And an HDMI TV. So how do I use the MacBook Pro and the TV as monitors?
We get variants on this question from time to time, and it’s one of the most frequently that I’m asked in person: someone wants to add a display to a Mac and they want to make use of what they have on hand instead of acquiring more hardware because of cost or space or sheer efficiency.
For Charles in particular, he must know through testing or by checking Apple’s support page for Target Display Mode that his iMac can’t act as a monitor. iMacs as far back as the 27-inch late 2009 model can engage this mode, which Apple explains how to use on that page. I know that folks who have such Macs often use them primarily as a computer, but then “dock” their laptop to have a larger second screen when they need to work on the laptop.(The article continues...)