800MHz memory on a 667Mhz iMac

Discussion in 'iMac' started by sbrekken, Jan 13, 2009.

  1. sbrekken macrumors newbie

    Joined:
    Jan 13, 2009
    #1
    I understand that the bus speed is fixed but will the faster memory damage my iMac or simply run at the slower 667mhz bus speed?
     
  2. Hellhammer Moderator

    Hellhammer

    Staff Member

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    Dec 10, 2008
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    Finland
    #2
    I think the mother board doesn't support 800MHz mem so yes it can damage your computer or not work properly. Just buy mem with same speed
     
  3. Bad Paper macrumors 6502

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    Apr 20, 2007
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    graphite clamshell
    #3
    Hellhammer is full of crap. The speed of the memory chip is simply the fastest (motherboard) speed at which it can reliably run. Putting "faster" RAM in the computer is not harmful; it is analogous to putting premium gasoline in a car that can run on the cheaper stuff.
     
  4. zygo macrumors member

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    Dec 17, 2006
    Location:
    UK
    #4
    I don't think it'll work. In theory it should, but for some reason 800MHz memory in a 667MHz machine doesn't work. At least not on the few I've tried-667 MacBooks and MacBook Pros. I would assume the same is true for the 667 iMacs seeing as they all use the same RAM and similar chipsets.
     
  5. zygo macrumors member

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    Dec 17, 2006
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    UK
    #5
    It shouldn't cause any damage-but the machine won't boot while it's installed.
     
  6. Sun Baked macrumors G5

    Sun Baked

    Joined:
    May 19, 2002
    #6
    Normally using the same class of memory, putting the faster memory in worked and got around the marginal memory problem.

    This round 800 won't work for 667 machines. Never bother to look at why the faster DDR2 memory was problematic this round.
     
  7. statik13 macrumors regular

    Joined:
    Jun 6, 2008
    #7
    Seemed to work for me. I put 4 gigs of 800mhz Kingston ram into my 667 iMac and it has been purring away for almost a month now.
     
  8. desantii macrumors 6502

    desantii

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    Sep 9, 2006
    Location:
    Aurora, IL
    #8
    I have also tried it (using 800mhz on 667mhz) and did not have a problem on an Imac.
    Now the interesting question is if the oppositee works, using 667 mhz on the latest Imacs(800mhz), why? you might ask. The cost of 4gb 667mhz dimms is much cheaper than the 800mhz and the performace difference should not be that great, definitely offset by more memory

    thnak
     
  9. fohawk17 macrumors regular

    fohawk17

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    Oct 17, 2008
    #9
    just because there is more memory doesnt mean that it will be better. why do you think the higher mhz run faster? cause of the higher number
     
  10. desantii macrumors 6502

    desantii

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    Sep 9, 2006
    Location:
    Aurora, IL
    #10
    Depending on your workload, 6gb of 667mhz will be faster than 4gb of 800mhz, specially if you do large images or have many VMs. Onc ethe machine sruns out of memory and uses the HDD for cache the access will be slower
     
  11. lixuelai macrumors 6502a

    Joined:
    Oct 29, 2008
    #11
    More memory > faster memory. There is very little difference between DDR2-667 and DDR2-800. Especially if the DDR2-667 is CAS 4 and the DDR2-800 is CAS 5. Now DDR2-800 is only a few bucks more so I'd just get it. But DDR2-800 does not play nice with some iMacs. Normally the RAM should be downclocked automatically but that does not happen. Same thing happens in the MBP 4.1.
     
  12. sbrekken thread starter macrumors newbie

    Joined:
    Jan 13, 2009
    #12
    Almost boots

    Thanks for all the info. Yes the two types of memory seem to be the same except for the speed. I can get my iMac to boot with the original 667 and one 800 but not both 800's. Any ideas????
     
  13. Bad Paper macrumors 6502

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    Apr 20, 2007
    Location:
    graphite clamshell
    #13
    Try switching the position of the 800s. Make sure it doesn't boot in both configurations. Also check that it will boot with the original 667 and *each* 800. One of your 800s may be bad.
     
  14. rayward macrumors 65816

    Joined:
    Mar 13, 2007
    Location:
    Houston, TX
    #14
    FWIW, I have a 2.8GHz iMac and recently upgraded the memory to 4gigs. I bought (and returned) memory chips from Crucial and the Apple Store and a few places in between, because my iMac wouldn't boot with the new memory installed.

    My iMac has an 800MHz front side bus, and I was being sold 800MHz (PC2 6400) chips. Finally the Apple Store figured out that I needed PC2 5300, which are rated at 667MHz. I plugged in a pair of those and al was good.
     
  15. DavyC412 macrumors member

    Joined:
    Nov 19, 2008
    #15
    it may or may not work, it depends on what the motherboard can support. if it doesnt work, i imagine it just wont work and not be damaging, but im not sure. i usually check the motherboard manual to see what clock speeds of ram will work stably with the MB, but i dunno how you can do that with apples logic board.
     
  16. iNotion macrumors regular

    iNotion

    Joined:
    Jun 5, 2008
    Location:
    Singapore
    #16
    hmmm...
    i am quite confused on the debate between 600 & 800mhz ram on the iMac...
    For my stock iMac 2.8Ghz with FSB of 1.07Ghz,
    it already comes with 2Gb ram 800mhz.(stock)

    A few mths ago, i max it up to 4gb ram 800Ghz and all is well till now.
     

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