iMac 21.5" as larger screen via target disk mode in OS X 10.5.8 works - mostly..

Discussion in 'iMac' started by sparkie7, Dec 14, 2009.

  1. sparkie7 macrumors 68020


    Oct 17, 2008
    .. along with some interesting anomalies..

    I'm traveling at the moment with my MBP 17". Arrived at my friends place who has a base iMac 21.5". Since I prefer to use the slightly larger screen to work off (even though my 17 MBP has more pixel density). So startup the iMac via TDM on my 17 MBP and to my surprise it works! - as my MBP only has leopard 10.5.8. I would have thought these iMacs would not run unless you have SL 10.6 loaded. It worked the 1st time, but crashed (grey vertical shade of death) twice after. On the 4th time it worked again. So that was weird (the inconsistency). Maybe 10.5.8 is NOT meant to be compatible with the new iMac's?

    There are a few things that don't work with this set up: the brightness control is set at one setting only (medium). I compared the geekbench and xbench scores of the iMac in 10.6.2 vs this TDM setup and the only thing lacking in scores was Processor integer performance 3565 vs 3401, Processor floating point performance 6381 vs 6093. And in XBench the CPU and Thread tests were marginally slower in the TDM setup (to be expected) but the interesting anomaly is that the OPenGL Graphics test is lower on the iMac stand alone test (140.88 frames/sec vs 258.80 frames/sec on the MBP TDM!) - very weird. Well apart from this one anomaly, it would seem SL is as to be expected optimised for the new iMacs.

    Once I get SL updater disks and update my MBP 17, then I expect the TDM route to be pretty seamless, unless there are some SL system & prefs inconsistencies b/w machine installs? ie MBP vs MP vs iMac

    One last anomaly I noticed is that with this set-up I am now seeing that I have full 4GB RAM in Activity monitor (instead of the 3.75 when I start up the iMac on its own and w/o TDM - as the 250MB apparently is used by the Graphics card). So, I am assuming that SL must be accessing the 250MB to work with the Nividia 9400, but 10.5.8 isn't? But still doesn't explain why the OpenGL test scores are actually slower (as above)

    Anyways, some geekery for those interested. Just good to know that the 21.5" can be used as a larger screen with its CPU power via TDM.

    Guess the  expert's can help answer some of the Q's and anomalies :)

    But for now I'll enjoy the flexibility of this set-up. Going to work on some intensive photoshop and graphics files and see if it stands up after some CPU and GPU bashing :D
  2. ZMacintosh macrumors 65816


    Nov 13, 2008
    wait, so you just connected your MBP via firewire and booted it up as an external drive or are you actually using the iMac screen via DisplayPort from both machines?
  3. kgeier82 macrumors 65816

    Feb 18, 2008
    I thought only the 27" had the DP input???
  4. xraydoc macrumors demi-god


    Oct 9, 2005
    I think what he's doing is booting the iMac off his laptop's hard drive, thus taking advantage of the iMac's faster processor and larger screen but using the contents of his laptop's HD.

    To the OP: I believe the new 16:9 iMacs (21.5" and 27") shipped originally with a special build of 10.6. Upgrade your laptop to 10.6.2 and you shouldn't have any more issues.
  5. sparkie7 thread starter macrumors 68020


    Oct 17, 2008
    what, xraydoc says. (btw i have a 17" MBP [non-unibody] with DVI port)

    yes, as i understand also

    Yes, correct

    I was surprised that 10.5.8 on my MBP worked on the iMac. I suppose I can't use the iMac's 10.6 install DVDs to update my MBP? [i'm thinking not and have to get proper SL installer disks]
  6. RosieB macrumors newbie

    Dec 24, 2010
    Using my exisiting iMac OS X 10.5.8 screen as a monitor for laptop?

    I am very untechnical so much of what I have read here is above my head, but in simple language, if I buy a new MAc Book Pro is there any way that I can use the 21" screen on my 2005 iMAc OS X as a monitor. I asked someone at Apple Store and was told that later models were fully compatible but that I would need special software, but he couldn't say what. Any help would be much appreciated as I shall miss my lovely screen but the computer itself is beginning to go slow.

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