Apple's New iMac Won't Feature With Target Display Mode, A Feature Allow iMac Use As An External Display
Apple has made it clear that the New 2017 iMac will not support the Target Display Mode, a feature which allows some iMac models that between 2009 and 2014 to use their built-in display as an external monitor for another Mac connected via Mini Display Port or Thunderbolt.
Apple for the first time to support this feature is on a Late 2009 27-inch iMac, which makes it easy to turn iMac into an external monitor, so even if iMac itself becomes obsolete, it still can be used as a monitor.
However, at the end of 2014, Apple stopped support this feature, the reason might be because a single Thunderbolt 2 Port may not be able to drive this new ultra-high resolution screen. Since then there haven’t any iMac to support the Target Display Mode.
Latest released New 4K, 5K iMac models support Thunderbolt 3 standard, means that the new models can have enough bandwidth to drive a 5K (5120 x 2880 resolution) display, the only question is whether Apple will support this feature.
An Apple Speaker told the media that the 2017 iMac is Not Designed to Support the Target Display Mode, clear that the feature will never return again. Apple has also clearly marked on its Support page states that "iMac (Retina 5K, 27-inch, Late 2014) and later iMac models will not featuring Target Display Mode displays."