MrHoffman wrote:
Servant of Cats wrote:
A 2013 iMac running in Target Display Mode requires Thunderbolt input, not Mini DisplayPort input.
That restriction existed from the beginning – unlike Apple's current restrictions on the OSes that the two Macs can run, and on the hardware release date of the other Mac. It seems very likely that it is a technical restriction and that the PC would need to be capable of producing Thunderbolt-encapsulated DisplayPort.
If the PC had Thunderbolt 3 or 4 output, a Thunderbolt 3-to-2 adapter ($50) plus a Thunderbolt 1/2 cable ($30) would run about $80. for the privilege of trying to reuse a ~10-year-old 21.5" iMac as a substitute for a 1080p monitor, with no guarantee of success. It might be better to put the $80 towards the purchase of a real monitor.
Odd. i can (and did) find all sorts of discussions of success with this configuration:
https://www.vidmore.com/record-video/use-imac-as-monitor/
https://www.technewstoday.com/how-to-use-imac-as-a-monitor-for-pc/
https://iboysoft.com/wiki/target-display-mode-imac.html
All three of those articles refer to the Thunderbolt requirement, although the first one does a very poor job of explaining it. This is a requirement for SOME iMacs that support TDM, and not for others. A Late 2013 iMac would be one subject to the requirement. The Apple Support document also clearly refers to this requirement.
Basically, if a Mac that supports TDM came with a Mini DisplayPort port – and did NOT have Thunderbolt – it could accept Mini DisplayPort input. If a Mac that supports TDM came with a Thunderbolt port, it could only accept Thunderbolt input. The Thunderbolt 1 ports on those Macs had the same physical connectors as Mini DisplayPorts, and could pretend to be Mini DisplayPorts for video output purposes. Apple never said that the ports could pretend to be Mini DisplayPorts for TDM video input purposes.
This means that the "24-inch and 27-inch iMac models introduced in 2009 and 2010" were more desirable as TDM displays than the "iMac models introduced in 2011, 2012, 2013, and mid 2014", because the former were able to accept Mini DIsplayPort video input (by virtue of their lack of Thunderbolt). In the early days, few PCs had Thunderbolt, and even many recent Macs only had Mini DisplayPort. These days, USB-C to mDP adapter cables are dirt cheap, but a TB3-to-TB2 adapter + a TB 1/2 cable will run you about $80. Intel's decision that moving Thunderbolt 3 to the USB-C connector was desirable, going forward, was justifiable, and not meant to screw over Thunderbolt 1/2 users, but it has had the effect of making TB3/4 to TB1/2 connections more costly.