2010 27in iMac used as display for Windows PC... Running Mojave or Catalina?

[natj910]

Hi guys, got a variant of this age old question that I couldn't find an exact answer for. I'm expecting a hard 'no' though lol

I've got a 2010 27in iMac I'm using in conjunction with a Windows PC. I use the iMac for uni so I don't get distracted by games & the like, and my Windows PC for everything else, with the iMac used as a monitor for the PC.

Now - I have noticed that the iMac changes to TDM the moment I plug in my PC's displayport cable, and only switches back if I turn off or unplug the PC. It will switch even while MacOS is still booting. Cmd+F2 doesn't work, although I am using an older wired Mac keyboard (could this be an issue?). So, my question is... Is TDM a purely hardware thing when driven from a non-Mac source?

If it is a purely hardware thing in this use case - will upgrading to Mojave or Catalina still stop TDM from working? I understand my GPU (HD5670) won't run these, but according to the dosdude guides the HD4850 should be OK with either OS, so I could fit one of those?

Admittedly this is kinda a 'for the fun of it' sort of thing, but having dark mode would be an absolute boon for my iMac; easier on my eyes for those long study sessions and subsequently worth the trouble. The darkchocolate and mySIMBL dark mode solutions for High Sierra just don't cut it lol

 

[Amethyst1]

Cmd+F2 doesn't work, although I am using an older wired Mac keyboard (could this be an issue?).

Yes. The command is actually Cmd+BrightnessUp, which may be mapped to F15 (or F16) on an older keyboard (it is on my circa 2003 A1048). So, try Cmd+F15 or Cmd+F16 just for kicks.

So, my question is... Is TDM a purely hardware thing when driven from a non-Mac source?

There's also a component in macOS, which is why the iMac has to at least have booted to the login screen for TDM to work - does yours switch even earlier?. Here's some technical detail on how switching into TDM actually works.

will upgrading to Mojave or Catalina still stop TDM from working?

Apple say switching into TDM was dropped in Mojave - I haven't personally checked if that is the case. I kept my 2010 27" iMac at High Sierra so I can hook up other systems in a pinch and use it as a display.

 

[natj910]

Yes. The command is actually Cmd+BrightnessUp, which may be mapped to F15 (or F16) on an older keyboard (it is on my circa 2003 A1048). So, try Cmd+F15 or Cmd+F16 just for kicks.


There's also a component in macOS, which is why the iMac has to at least have booted to the login screen for TDM to work - does yours switch even earlier?. Here's some technical detail on how switching into TDM actually works.


Apple say switching into TDM was dropped in Mojave - I haven't personally checked if that is the case. I kept my 2010 27" iMac at High Sierra so I can hook up other systems in a pinch and use it as a display.

I didn't know that about the Cmd+BrightnessUp - thanks. Still didn't work though, on either keyboard I have - it's mapped to F15 on my Mac keyboard, Pause/Break i.e. F15 on my K70 Mk2, works on neither. Unfortunately, I don't have an Apple Wireless or Magic Keyboard, although I could probably borrow one from work for testing if need be.

I just checked the bootup thing. A lot harder now it has an SSD in it lol, but didn't work. Did the black screen flash thing when I plugged it in, but went back to macOS instead of showing the Windows PC when it finished booting. I must have been wrong there, I thought it did it the other day but maybe not. My short term memory is shithouse TBH.

I was under the same impression re: Mojave TDM support, but I keep reading about people who supposedly have it working on later versions and that it was completely removed in Catalina. Wonder if there's a way to mess with SMC to patch it in... Either way, I'll have a read of that link and see if I can figure this out. Thanks for your help!

 

[Nguyen Duc Hieu]

I've just experienced new things when changing my Windows PC.

Old PC: HP Prodesk 600G1 SFF
Windows is a WindowsToGo version on a USB enclosure.
When the PC sleeps, iMac screen is on.
If I wake the PC first, then the iMac, TDM stops, each machine displays its own content. If I sleep and wake it up again, TDM kicks in again.

New PC: HP Elitedesk USDT (the mini one)
I moved the SSD inside the case, running in SATA mode.
When plugging the PC to the iMac, TDM auto kicks in.
When I sleep the PC, iMac screen stay black.
Even when I removed the DP cable or turn off the PC, the iMac stay black.
Maybe it's the difference of DP port circuit on the PCs that caused the weird acting on the iMac.
Maybe it's the graphic card that cause this.
I don't know. A little annoying in switching back to Mac, that's all.

 

[natj910]

I've just experienced new things when changing my Windows PC.

Old PC: HP Prodesk 600G1 SFF
Windows is a WindowsToGo version on a USB enclosure.
When the PC sleeps, iMac screen is on.
If I wake the PC first, then the iMac, TDM stops, each machine displays its own content. If I sleep and wake it up again, TDM kicks in again.

New PC: HP Elitedesk USDT (the mini one)
I moved the SSD inside the case, running in SATA mode.
When plugging the PC to the iMac, TDM auto kicks in.
When I sleep the PC, iMac screen stay black.
Even when I removed the DP cable or turn off the PC, the iMac stay black.
Maybe it's the difference of DP port circuit on the PCs that caused the weird acting on the iMac.
Maybe it's the graphic card that cause this.
I don't know. A little annoying in switching back to Mac, that's all.

That's actually pretty interesting, I haven't noticed it cause my PC is set to not go to sleep, just switch off the display. Basically it does exactly what I tell it to, goes black when the PC shuts it off, but when the PC is shut off or I unplug it's straight back to macOS (the login screen, to be exact.

Mine is a custom build, Ryzen 5 3600X, 32GB RAM, R9 390, booting off a nVME drive. So aside from the GPU, all pretty recent. Be interesting to see how it goes into the future with GPU updates, etc.