Share Thunderbolt Monitor between Two Computers

Discussion in 'Mac Accessories' started by paulrbeers, Jan 5, 2012.

  1. paulrbeers macrumors 68040

    Dec 17, 2009
    I have three thunderbolt enabled macs (see signature). I often times use my Macbook Air and my Mac Mini while sitting at my desk. I don't use them "at the same time", but rather switch between then. I would love to buy the Thunderbolt display and use it for both and "switch" between them (i.e. one hooked up via the built in thunderbolt cable and pick up another thunderbolt cable to hook the other up via the thunderbolt port). Here are my questions:

    A. is it even possible?
    B. how do I switch between which computer is using the screen?
    C. what about anything plugged into the display, I would assume only the "target" computer gets access to it?

    I've thought about just dumping the Mac Mini if it isn't possible and go with an iMac instead and use target display mode. I might go that route if this isn't possible.
  2. sampers macrumors member

    Apr 7, 2010
  3. iVoid macrumors 65816

    Jan 9, 2007
    Keep in mind using a Displayport KVM will work to switch the display between two computers, but you loose all the thunderbolt capabilities (the ports on the TB display, the daisy chaining of TB devices from the two TB ports).

    Only way to retain the TB capabilities would be to switch the cable back and forth. (no TB switches available and not likely for a while, if ever).
  4. Lennyvalentin macrumors 65816


    Apr 25, 2011
    I don't think that would work at all. The TBD does not accept plain Displayport video input, it must come packaged as a thunderbolt data signal. Connecting a KVM inbetween the Mac and the TBD would turn the Mac's TB output into displayport out, and that doesn't work with the TBD. I've tried it on my own gear, and nada.

    I don't know what happens if you hook up a thunderbolt Mac using Apple's TB cable to the TBD's daisy-chain port though. I've not had any surplus money to throw at that extraordinarily expensive cable. There's a very very slim chance it might work if the main TB cable isn't connected, or at least if the device it is connected to is powered off. I wouldn't bet the farm on it though by any stretch; the daisy-chain port is probably designed as an output only, relegating the TBD as a one-device-only monitor.

    On the other hand, Samsung's S27A850D, which I also own and is REALLY nice, both in design and performance, can show the video output of two computers simultaneously. It also has a USB3 hub built-in, giving it 5Gbit/s I/O capability once Apple finally releases some USB3 Macs.

    It only has one Displayport input though, so if you want to plug two Macs into it and one isn't a Mac Pro you'll need a dual-link capable DVI to DP converter, and those are a bit costly.
  5. August51 macrumors newbie


    Nov 17, 2009
    No, the TB port on the TB display is not output only. I just now set up my MacBook Pro with a TB cable to a TBD TB port and the built-in cable of that TBD connected to an iMac.

    [MacBook] =-----= [Thunderbolt Display] O-----= [iMac]
    TB cable ------^ Built-in cable from TBD ----^

    I could NOT get the MacBook to recognize both external "monitors" even when I put the iMac to "sleep".

    However, the MacBook could indeed display on the iMac when I put it into Target Display Mode (Cmd+F2). So the daily chain was passing things through but the iMac controlled the TBD. All the iMac windows and screens moved to the TBD where it seemed like everything was working, I could log in and see all my windows and the mouse worked for all window controls and menus, ...

    BUT the keyboard would only recognize "a", "A", Option+A, and Cmd+A. Weird, when I could log in, right? (I assure you that my password has different characters than those.) I tried both USB and Bluetooth keyboards and the on-screen keyboard with the same results. That's one weird bug and I'm trying to find out how to report it to Apple.

    I did NOT try turning the iMac off. I presume that because of the direct connection from the MacBook to the TBD, it would indeed work as an external monitor for the MacBook, but I didn't try it because having the iMac off won't work for how I want to use them.

    I hope this helps,

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