Thunderbolt, MiniDisplayPort, Target Display Mode = ????

February 21, 2012 8:58 AM

I have a late 2010 Macbook Pro (MacbookPro6,3) running Lion (10.7.3) and an iMac of indeterminate vintage (iMac11,3) running Snow Leopard (10.6.8). I have a Thunderbolt cable. Neither mac supports Thunderbolt; both have MiniDisplayPort connectors. I want to run the iMac in Target Display Mode as a second display for the MacBook Pro. Can I make this happen?

I know that the iMac supports Target Display Mode with a MiniDisplayPort <> MiniDisplayPort cable. The tech at my campus Apple store sold me a Thunderbolt cable (same connectors as MiniDisplayPort, but with active electronics, right?). Target Display Mode is not working -- I press cmd+F2 on the iMac and nothing happens. I can see several potential problems: 1) different OS versions interfering with target display mode. 2) thunderbolt cable is incapable of acting like a passive MiniDisplayPort cable.

Do I need to search out an old MiniDisplayPort cable to make it work, or is this doomed to fail because of the mismatched OSes?

posted by Alterscape to computers & internet (6 answers total)

According to this this support page from Apple, what you're doing should work, since "a converter that converts other electrical, video, and audio protocols from another source device to Mini DisplayPort compliant signals" is acceptable.

If you want to eliminate the cable as the issue and you can wait a few days for shipping, you can get an ordinary Mini DisplayPort cable on Monoprice.com for around four bucks.
posted by bcwinters at 9:51 AM on February 21

Ordered. There's no reason I NEED a Thunderbolt connector, and $6.50 shipping inclusive is a hell of a lot better than $50+ tax (thank you campus store).
posted by Alterscape at 10:16 AM on February 21

Unless something has changed in software, it is *not* the case that all iMacs can run in target display mode (i.e. serve as a display for an external computer). I had an iMac that I got in late 2008 that explicitly did not allow this. This article seems to suggest that "Late 2009" iMacs are the first to support this.
posted by Betelgeuse at 10:26 AM on February 21

Your iMac shouldn't have any problem, then.

Try the MDP cable. If it doesn't work, Google. If it's actually a flaw, it will be discussed in the Apple forums. They're incredibly comprehensive. Seems like Apple folk are more likely to take to support forums than others.
posted by supercres at 11:10 AM on February 21

When I returned the Thunderbolt cable, a different tech was on duty -- he claimed that actually it's MDP that's active, not TB. Ah well, we'll see if this works when the new MDP cable shows up. Thanks for the advice, all! I'll report back after I get the new cable and try it out.
posted by Alterscape at 11:30 AM on February 21

Just a follow-up to say that I got the Monoprice MiniDisplayPort cable in the mail and it worked exactly as you said, bcwinters. Thank you!
posted by Alterscape at 2:41 PM on March 1