Power consumption of Target Display Mode compared to monitor use.
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Power Consumption of Target Display Mode in 2009, 2010 iMac 27s
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Juicy Box
macrumors 604
Thanks for posting that.
I was curious about this myself, specifically about how much less the power consumption would be for the slower processors.
I knew that the Late 2009 to Mid 2010 27" iMacs would consume a lot more energy than a modern monitor, but depending on the usage, it still could worth it to some to use an existing iMac in TDM than to buy a new monitor.
As for buying an iMac to specifically use in TDM, it probably wouldn't be worth it for most people, unless they really like the iMac aesthetic or didn't use it that often.
For myself, I was thinking of retiring a power hungry 2006 Mac Pro 1,1 that I current use as a Plex Media Server, and replacing it with my M1 MM. But, this wouldn't happen until I replace my M1 MM with a M2 MM or maybe a next generation Mac Studio when it comes out.
My Mac Pro is currently headless, sitting in my cold basement, and I would probably keep my M1 MM headless as well, but I thought about maybe getting an old Mini DisplayPort iMac to use as a display when I didn't want to use Screen Sharing.
I even thought about using the old Mini DisplayPort iMac as my Plex Media Server until I figure out my next iMac. Use the iMac as a display when I need to, but mostly run it with the display sleeping.
Wonder what the power consumption would be with the iMac on, but the display a sleep?
I was curious about this myself, specifically about how much less the power consumption would be for the slower processors.
I knew that the Late 2009 to Mid 2010 27" iMacs would consume a lot more energy than a modern monitor, but depending on the usage, it still could worth it to some to use an existing iMac in TDM than to buy a new monitor.
As for buying an iMac to specifically use in TDM, it probably wouldn't be worth it for most people, unless they really like the iMac aesthetic or didn't use it that often.
For myself, I was thinking of retiring a power hungry 2006 Mac Pro 1,1 that I current use as a Plex Media Server, and replacing it with my M1 MM. But, this wouldn't happen until I replace my M1 MM with a M2 MM or maybe a next generation Mac Studio when it comes out.
My Mac Pro is currently headless, sitting in my cold basement, and I would probably keep my M1 MM headless as well, but I thought about maybe getting an old Mini DisplayPort iMac to use as a display when I didn't want to use Screen Sharing.
I even thought about using the old Mini DisplayPort iMac as my Plex Media Server until I figure out my next iMac. Use the iMac as a display when I need to, but mostly run it with the display sleeping.
Wonder what the power consumption would be with the iMac on, but the display a sleep?
The 2009 and 2010 27 inch iMacs only have one MiniDisplayPort so you can't do TDM and have an external display connected at the same time.
You can run macOS and TDM at the same time and flip between the two.
You can probably do screen sharing to the iMac while it's in TDM.
TDM doesn't work without macOS because macOS is needed to do the switch. For 2009 and 2010, the DisplayPort switch can be done in Linux. For Thunderbolt iMacs, Linux doesn't have the code needed to do the Thunderbolt switch.
I think that I have done screen sharing with an iMac in TDM mode. I have several videos on screen sharing with old Macs and have done lots of experiments.
I've never had the 2011, 2012 or 2013 iMacs so I've never had the opportunity to play with Thunderbolt and TDM.
Thunderbolt TDM has a DisplayPort switch to switch the iMac's display from the GPU to the DisplayPort Output Adapter of the Thunderbolt controller. I suppose this is similar to the switch that is used for DisplayPort TDM.
In addition to the DisplayPort switch, the Thunderbolt TDM code in the iMac and in the source Mac also have to somehow setup a tunnelled DisplayPort path that crosses the Thunderbolt domain boundary between the two Macs.
Normally, a tunnelled DisplayPort path doesn't cross a Thunderbolt domain boundary - the Thunderbolt dock or Thunderbolt display that is the destination of the path (where the DisplayPort display is connected) belongs to the domain of the host Thunderbolt controller. The host Thunderbolt controller has a DisplayPort Input Adapter and it knows where all the DisplayPort Output Adapters are located in its domain. I don't know how a path is setup to cross domains. I suppose the iMac can send info about how to setup the path to reach the DisplayPort Output Adapter that is located in its domain? Or maybe it's simpler than that. For example you could have iMac->dock <-> dock ->Mac where the domain boundary is between the two docks - yet Thunderbolt networking works in that case. A path needs to be setup for Thunderbolt networking. It could be just as easy to setup a tunnelled DisplayPort path. Linux and Windows can both do Thunderbolt networking but they don't have code for Thunderbolt Target Display Mode.
It seems to me that a Thunderbolt dock could be turned into a KVM. Two Macs can connect to it. The dock belongs to one of those two Macs. The owner Mac is able to output to the display. Some kind of software could make the owner Mac give up ownership of the display so the other Mac can display to it. Basically, the tunnelled DisplayPort path to the Mac is released and a new tunnelled path is created that connects the display to the other Mac. Maybe the same thing can be done for the tunnelled PCI paths so that the ownership of connected devices (keyboard, mouse, storage devices) will also switch to the other Mac. Or maybe the domain boundary can be moved entirely so that ownership of the dock (including the attached display and USB devices) passes to the other Mac.