I have the requisite model iMac -Late 2009 iMac, and a brand new PC build employing AMD Threadripper and a GTX1080. I would like to use the iMac as a display in target disk mode from the PC/

The GTX1080 outputs to three DP's(DisplayPorts) and an HDMI. I have tried TDM using a DP to MDP(MiniDisplayPort) cable but have not succeeded in getting past the floating Firewire logo that TDM shows on this iMac build.

I see on Apple's forums it is specifically mentioned that MDP to MDP cable is to be used, and yet, I can find no evidence on the web to suggest that there's any actual difference in the data transmission between DP & MDP.

Is this configuration supported?

  • ...floating Firewire logo? That sounds like Target Disk Mode, not Target Display Mode. I've had success with the same iMac going to an R9 Fury in a Windows build. Also just confirming that it's a 27" iMac? – JMY1000 Dec 19 '17 at 0:52
  • Yeah, its an "iMac (27-inch, Late 2009)" as copied from my 'about this Mac'. Ok, thank you, yes I was setting it up as Target Disk Mode... doh! Now, doing the command F2 thing all I get is a black screen. I probably should have mentioned that there is no OS on the PC as yet (hence the need to do TDM in the first place), and so the PC is (probably) wanting me to access the BIOS. Would this have any effect on why there's just a black screen? – devtank Dec 19 '17 at 2:47
  • For me, the iMacs would automatically switch to video from my tower as soon as it started, as long as the displays started off but not asleep–no command+F2 necessary (that seemed to only be needed with other Macs), and it displayed a BIOS just fine. – JMY1000 Dec 19 '17 at 3:04
  • Interesting. I'll try this now. – devtank Dec 19 '17 at 18:43
  • OK, well the iMac went black as soon as I booted up the PC, but then cut back to OSx as though Id physically pulled the DP cable. FYI This is an AMD Threadripper so there is no other video, other than the GTX1080 that I have installed. – devtank Dec 19 '17 at 18:47

Target Disk mode is booting with a T and the OS not running. You will see a FireWire / USB / Thunderbolt icon in this target mode on supported iMac.

Target Display mode has no icons and needs the Mac OS to be running and is entered with either Command - F2 or Command - Fn - F2 keys.

The link above has all the steps to qualify / check your connections and requirements.

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  • OP already confirmed that even when doing it properly that he's getting a black screen, so something else is up. – JMY1000 Dec 19 '17 at 4:39
  • @JMY1000 It's not clear to me that you would see the FireWire icon when entering TDM so I wanted to put up some sort of answer in case it's helpful. Are you saying TDM works without any operational OS running on the Mac end? – bmike Dec 19 '17 at 12:32
  • I have already read and re-read that Apple page. – devtank Dec 19 '17 at 20:21
  • @bmike Not saying that, just that even when they boot into macOS and do it properly it doesn't work (per their comments.) – JMY1000 Dec 19 '17 at 21:06

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