Quad Core (Nehalem) iMac: where's the triple channel RAM?

Discussion in 'iMac' started by Styxie, Oct 20, 2009.

  1. Styxie macrumors member

    Joined:
    Oct 29, 2008
    Location:
    Holland
    #1
    Now, I'm not that sure about my CPU knowledge, but as I understand the new Nehalem processors can use triple channel memory (instead of dual memory used by the C2D Macs). So why does the new Core i5 or i7 iMac have 4GB of RAM standard? That's not divideable by three, so I'm guessing they're not using the triple channel thing. If you remember, the Mac Pro's do come standard with either 3GB or 6GB RAM. I dont geddit...
     
  2. Salavat23 macrumors 6502

    Joined:
    Feb 7, 2008
    #2
    Because the i5 and i7 CPUs used in the iMac are based on the P55 platform. They only support 1 or 2 channels.

    If you wanted 3 channels, you need a 900-series Core i7 or a 3000/5000 series Xeon.
     
  3. cloudstrife13 macrumors member

    Joined:
    Aug 13, 2007
    #4
    It looks like the chips in the iMac are the Core i7 860 and the Core i5 750 they only have dual channel DDR3 memory controllers on them.

    But they do support DDR3 1333MHz when the other i7's with tri channel only officially supported DDR3 1066MHz.

    Most tests show that real world performance doesn't really change too much.

    Here's a good review on the Core i7 860: http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3641
     
  4. Palliser macrumors regular

    Joined:
    Jul 28, 2007
    Location:
    USA
    #5
    this is good to know... I was seriously considering waiting till next year to grab a new(er) iMac. But if it really doesn't make much of a difference that is good to know.
     
  5. Cave Man macrumors 604

    Cave Man

  6. canyonblue737 macrumors 6502a

    Joined:
    Jan 10, 2005
    #7
    the i5 2.66 is the i5-750 and the i7 2.8 is the i7-860 when you look at charts. the "8xx" series i7's don't do 3 channel memory, you need to step up to the "9xx" series for that. after having read a ton of i5/i7 info/reviews it seems i can summarize it like this:

    1. i5/i7 will give a reasonable boost over core 2 duo in every day applications immediately.
    2. 3 channel memory vs. 2 channel memory accounts for only a tiny performance boost and likely isn't a big loss on the i7 end.
    3. i7 offers hyper threading allowing for 8 virtual cores and i5 doesn't. this won't amount to much until more applications can handle high numbers of cores and use grand central dispatch in leopard, so i5 vs. i7 right now isn't a huge difference. however the difference will grow in time and clearly the i7 is the more future proof CPU if you intend to keep your iMac for some time.

    i went i7, a $500 increase over the core 2 duo but for me it is worth it because i intend to use the computer for several years and will run video / photo software i think will grow to use the power of the i7. if i was on a tighter budget i would have been happy with the i5 but at this point i would simply not want to buy another core 2 duo, it is 3 year old technology and has many downsides moving forward.
     
  7. twoodcc macrumors P6

    twoodcc

    Joined:
    Feb 3, 2005
    Location:
    Right side of wrong
    #8
    after looking that review, i agree. the 860 is slightly faster than the 920
     
  8. pblanton macrumors newbie

    Joined:
    Mar 5, 2009
    #9
    I agree with canyonblue737. I also went with the i7 (still about two weeks out). I am a Microsoft .NET developer that must use Windows 7 on a daily basis, but am about a year-old Mac convert. Windows 7 LOVES the Core i7 and since I still have to use Windows, I am happy to be getting it.

    That said, the Core 2 DUO in my unibody Macbook Pro also runs Windows 7 like a rocket-sled on rails. My Macbook has been the best Windows machine I have ever had. :)
     

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