800 MHz SO-DIMM RAM for new iMac?

Discussion in 'iMac' started by jmillar, Oct 3, 2007.

  1. jmillar macrumors newbie

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    Jul 20, 2007
    #1
    800 Mhz SO-DIMM ram is widely available now to match the FSB of the Santa Rosa Core 2 platform used in the iMac. Will a new aluminium iMac recognize it and clock it properly? 677 RAM was the initial spec due to a lack of suitable RAM when it hit the stores.
     
  2. RevToTheRedline macrumors 6502a

    RevToTheRedline

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    #2
    800Mhz is just the speed of the FSB. Putting PC2-6400 DDR2800 ram in the new iMac won't do anything, but make you spend more money for nothing.

    PC2-5300 is all you need
     
  3. kearneyTaaffe macrumors newbie

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    #3
    Well Said

    Well said Rev, also it should be noted that the new iMacs do not support dual channel memory.
     
  4. nawks macrumors newbie

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    #4
    :eek: i didnt know that! for real?
    forgive me for asking, i'm not really knowledgeable regarding hardware. but is it a "they don't support it now" or "they will never support it" kinda thing?
     
  5. flopticalcube macrumors G4

    flopticalcube

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    #5

    Attached Files:

  6. Luthcon Sloan macrumors newbie

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    #6
    First of all: Hi! I am new and a prospective iMac buyer soon when Leopard ships with them.

    I was also wondering why the memory speed does not match the FSB when the new iMacs have been introduced. Judging from the chipset specs the questions really comes up if PC6400 memory would be of any benefit, assuming iMacs can detect it properly and use it with the higher FSB throughput which could be achieved?

    Or maybe I am still too much a PC dude and worry too much about such things... :confused:
     
  7. flopticalcube macrumors G4

    flopticalcube

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    #7
    The limitation appears to be in the memory controller. The desktop chipset specs 800MHz max whereas the mobile specs 667MHz. I would trust Intel on this one and say 667 is the max.
     
  8. CanadaRAM macrumors G5

    CanadaRAM

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    #8
    Welcome to Mac Rumors, J, N, K and L

    First thing -- please search the forums for answers before posting, we have covered this perhaps 25 times in the las two months alone.

    At the top of the page, you'll see a tab called "Guides" - most frequently asked topics have a MR Guide written on them

    MR Guide to understanding Intel Mac RAM
     
  9. Luthcon Sloan macrumors newbie

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    #9
    Thanks for the quick reply, sounds reasonable. Thank you!

    Oh dear, I am just looking forward soo much switching to OS X I can hardly stand it anymore! :apple:
     
  10. RevToTheRedline macrumors 6502a

    RevToTheRedline

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  11. nyc2socal macrumors newbie

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    Sep 28, 2007
    #11
    For the longest, Crucial had the 800mhz up on their website as compatible.. According to some posters on the support forums, it would only recognize 3GB out of the 4GB installed..

    In the end, if you check Crucials web site now, they only advertise the 667mhz memory.. I take that as 667 is the only way to go..
     
  12. RevToTheRedline macrumors 6502a

    RevToTheRedline

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    #12
    The only thing I can think of 800mhz ram being good for (if you really wanna spend the extra cash money)

    Back when I used to build PC's I would buy much higher speed ram then I'd actually need, so I can run it's CAS latency very low, for example a stick of ram rated at CAS 5 (for example PC2-6400 DDR800) will probably run in CAS 3.5 or CAS 4 at 667Mhz

    Meaning you will see a tiny big of performance increase, I'm not talking 15-20%, but a little.

    Although, the way I obtained that with custom PC's with changing the whole bios memory latency configuration, I dunno if an iMac will automatically take advantage of this.
    The memory that comes standard in the iMacs is Hyundai Electric PC2-5300 with a CAS of 5 at 667mhz.
     
  13. oiskinhead macrumors newbie

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    Sep 2, 2007
    #13
    You should always match fsb and ram speeds closely for the best possible performance and to avoid bottlenecks in the system. Santa Rosa chipset does support 800 MHz memory and the iMac is based on that chipset. Apple's not the only one introducing and selling mismatched fsb/ram configurations, Dell and Sony use to do the same thing, be it to cut costs or because of low initial availability of specific new memory at the time a new product is introduced to the market, in this case the Al iMac. Going from 667 to 800 Mhz, you shouldn't see that much performance/speed increase anyways unless you're deep into gaming where every bit of speed increase counts, otherwise, quantity is better than speed.
     
  14. flopticalcube macrumors G4

    flopticalcube

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    #14
    Prove it.

    iMac is PM965 (Crestline) based. The desktop chipset is P965 (Broadwater) based.
     
  15. CanadaRAM macrumors G5

    CanadaRAM

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    #15
    How much RAM is recognized is completely independent of the RAM's speed.

    Pls read the Guide that was linked.

    CoreDuo machines will recognize 2 Gb (2 x 1 Gb)

    Core2Duo machines will recognize 3.3 of a total 4 Gb (2 x 2 Gb) in Dual Channel mode. OR 3 Gb (1 Gb + 2 Gb ) in Single channel mode

    Core2Duo SantaRosas can recognize the full 4 Gb of a 4 Gb install (2 x 2 Gb).

    There has never been any evidence that Macs since 1994 have automatically adjusted for lower latency operation when lower latency capable RAM has been installed. And since there is no BIOS to adjust there is no way of knowing, or forcing an intel Mac's latency settings.

    Since the RAM bus is limited by the 667 MHz hardware RAM controller on these machines, 800 MHz RAM is not going to do a thing.
     
  16. nyc2socal macrumors newbie

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    Sep 28, 2007
    #16
    And I completely agree. The example I gave was someone with a SantaRosa Core2Duo that installed 2x2GB 800mhz chips from Crucial into a 24" 2.8. The iMac only recognized 3GB for some odd reason. When the user called Crucial and explained the problem, Crucial acknowledged that there was an issue with 800mhz chips in the iMacs. A day or two later, the option for the 800mhz chips went off the memory advisor tool for the 2.8 @ Crucial.. It use to be the "recommended" option, but now it only displays the correct 677mhz.
     
  17. oiskinhead macrumors newbie

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    Sep 2, 2007
    #17
    :D Oooops!! should've read the guide before jumping to conclusions...my bad! It's just the way it has been done before. Too bad intel didn't include support for 800MHz memory for this chipset. There are some IBM laptops apparently using pc6400 memory in Santa Rosa boards, read all about it in notebookforums.com ...:apple:
     

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