1066Mhz DDR3 Ram down clocked by Mac Pro to 800Mhz!!!

Discussion in 'Mac Pro' started by All Taken, Sep 17, 2010.

  1. All Taken macrumors 6502a

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    #1
    I purchased 3 sticks of 1066Mhz DDR3 ram for my 3.2Ghz Nahalem Mac Pro. The sticks were perfect and have the temperature sensors on board, it's hynix ram and is ECC Registered.

    I decided to buy a fourth stick making 16GB 4x4GB - When I installed the fourth stick the Mac down clocked the ram to 800mhz!. Any idea why? or better yet, how to get it running at 1066mhz again?

    I have tried using the new stick on its own and it's fine running along at 1066Mhz, if you add a fourth stick with any module being that fourth stick it auto downclocks the ram......

    Many Thanks
     
  2. linuxcooldude macrumors 68020

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    Mar 1, 2010
    #2
    The Mac pro uses a triple channel memory controller that is optimized to use three DIMM's.

    Adding the fourth DIMM forces the CPU to split the memory bandwidth between the third and fourth DIMMs, which drops the effective throughput to those DIMMs.

    The vast majority of applications don't saturate the memory bandwidth. If more memory is a priority I would not worry about lower memory speed.

    To get it back up to 1066Mhz speed would have to remove fourth DIMM and use 8 GIG DIMMS. Not sure if mixing of different size DIMMS in the three channels will effect anything.
     
  3. Umbongo macrumors 601

    Umbongo

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    #3
    First I'd find out if your memory is single rank, dual rank or quad rank. Also check what voltage each DIMM is: 1.35 or 1.5. Check each DIMM is exactly the same in those regards. There are a few ways where memory will run at 800MHz. Unfortunately as registered memory isn't supported on X58 boards (single processor) there is no documentation for it, just for dual socket ones.
     
  4. All Taken thread starter macrumors 6502a

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  5. cjoy macrumors member

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    Oct 24, 2008
    #5
    just stumbled over the above statement. :eek:
    can someone clarify wether the 2x8GB kit would work in a 2010 quad (2,8)?

    Kingston ValueRAM
    KVR1066D3Q8R7SK2/16G

    DIMM
    SDRAM-DDR3 - 1066 (PC3 - 8500)
    ECC-Support
    Registered
    CL 9
    240-Pin
    1024Mx72
    1,5 Volt (1,48 Volt - 1,52 Volt)
    Quad Rank x8
    Thermal Sensor


    also the whole quad-rank thing is not entirely clear to me... will this impact a future upgrade to 24GB (3 modules) of this type?
    thanks.
     
  6. Umbongo, Jan 18, 2011
    Last edited: Jan 18, 2011

    Umbongo macrumors 601

    Umbongo

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    #6
    Three quad rank modules will be fine. Adding a fourth would downclock it all to 800MHz.
     
  7. cjoy macrumors member

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    Oct 24, 2008
    #7
    actually the quad ranks are offered 50% cheaper than the identical kingston modules with dual rank... since I have no plans to go beyond 24GB (3x8) on this machine, this is good news.

    thank you very much.
     
  8. Umbongo macrumors 601

    Umbongo

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    #8
    Yeah edited my post after I checked prices.
     
  9. handheldgames macrumors 6502a

    handheldgames

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    Apr 4, 2009
    #9
    That should not be happening.... I am running 4x4GB sticks for 16gb@1066 on a 2009 MacPro Quad.

    IF your original set is a triple channel part, you must add an identical part to make it properly function. I had a similar issue adding in a part of OWC that was not matched, except my MacPro would not even boot up. Once I had the right chip, I was running just fine.

    Based on the benchmarks, the benefits in triple channel vs dual channel are so insignificant, it was more of marketing hype than anything that equates to a measurable boost in the user experience.
     

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  10. cjoy macrumors member

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    Oct 24, 2008
    #10

    keep in mind this is not about tripple/dual channel, but the type of memory itself. there have been conflicting statements concerning certain module types (quad-rank, registred) - this has nothing to do with dual-channel or triple-channel support.
     
  11. handheldgames macrumors 6502a

    handheldgames

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    Apr 4, 2009
    #11
    Exactly... But if you have ram rated for triple channel, you must get a 4th chip of the same type for it to properly work in the 2009 MacPro. This is probably why the RAM is slowing down - I'd call it lucky that it even works.
     
  12. cjoy macrumors member

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    Oct 24, 2008
    #12
    ram itself is not "triple-channel".. thats just marketing dust on the kits they sell. as long as the rank-type and size are equal, you can mix any ram from any brand you like and maintain triple channel support.. thats a chipset feature and not bound to certain ram modules.

    if, however, you add a fourth module the triple channel access to ram is no longer supported, as #3 and #4 have to share a lane... but again, this happens also when adding a module from a ram kit labled "triple channel bla kit"
     
  13. Umbongo macrumors 601

    Umbongo

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    #13
    Using quad-ranked DIMMs while also using more than one slot on any channel will see speed drop to 800MHz. This is a technical limitation of the platform. Doesn't matter if they are matched, or if you have 4, 5 or 6 DIMMs on the memory branch.
     
  14. cjoy macrumors member

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    Oct 24, 2008
    #14
    does that mean using 2 quad-rank modules in a nehalem quad would result in the mentioned speed drop?

    thanks,
    cj
     
  15. fabriciom macrumors 6502

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    Madrid, España
    #15
    So what ram modules should I use if I want to go 24gb (6x8) in a 2009? Can someone specify some models?

    -Thanks
     
  16. Umbongo macrumors 601

    Umbongo

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    #16
    It is only when you have more than 1 on any channel. So with only 2 you'd have one on channel 1 and one on channel 2. No problem here. Really it's only when using 4 or 8 on Mac Pros that there should be any issue.
     
  17. Umbongo macrumors 601

    Umbongo

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    #17
    KVR1066D3Q8R7SK3/24GI - That is a 3x8GB kit of quad ranked 1066MHz registered DIMMs with the thermal sensor. Goes for about €400. I can't say that anyone has tested it, but there is no technical reason why it won't work, Mac Pros aren't any more picky than other Intel systems and you can just return it using the EU distance selling laws (within 7 days) if there was any problem. Crucial are like twice that price.
     
  18. handheldgames macrumors 6502a

    handheldgames

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    Apr 4, 2009
    #18
    Just head over to macsales.com (other world computing) They have a great interface for selecting ram for the Mac Pro, it's that simple....

    Btw... Im running all 4 slots at 1066, not 800.
     

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  19. Umbongo macrumors 601

    Umbongo

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    #19
    OWC are great, but if you only plan on using 3 or 6 memory slots you can save 33% on the cost of 8GB DIMMs by going quad-ranked. 48GB of Kingston memory would be €800 vs around €1250 imported to Spain from OWC.

    :) All of the memory branded as suitable for the Mac Pro will be dual or single rank so shouldn't have issues. This only applies to those who want to save money by getting non-certified memory.
     
  20. fabriciom macrumors 6502

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    #20
    Will be purchasing that kit as soon as I finish paying for the 2 CPUs I just upgrade my mac pro with.
    Thanks for the info!
     
  21. MacMolly macrumors newbie

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    SF BAY area
    #21
    Safe to MIX?

    My first Mac Pro Quad has always run with 4 x 4 @1066 Mhz. About a week ago, I picked up a large amount of Hynix 4 GB chips and yesterday a 2nd Mac Pro arrived. I popped in 4 of the new sticks and sure enough, everything dropped to 800 mhz and back to 1066 mhz when I removed the 4th stick. I spent half a day (literally) trying to figure out what was wrong before I stumbled upon this post.

    I figured out on my own that the sharing of the 3rd & 4th sockets with "some" RAM brought everything down to 800mhz. But I also found out that "apparently" I could use 2 sticks of the "new" RAM in slots 1 & 2 and 2 sticks of the "old" RAM in slots 3 & 4 and end up with 1066mhz registering.

    Two questions:

    1) Is the RAM that down regulates to 800 Mhz called "quad core", and, if so, what type of RAM doesn't do that?

    2) Is it ok (wise) to mix and match to get to 1066 Mhz. Seems like a cheaper alternative to use a 50/50 split.
     
  22. Umbongo, Jan 31, 2011
    Last edited: Jan 31, 2011

    Umbongo macrumors 601

    Umbongo

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    #22
    It is "quad-ranked". Other types are dual-rank and single-rank. You may see it as SR, DR or QR withing a model name or list of specs.


    If it works, it works.

    My guess would be that it works on the Mac Pro because there is nothing put it place in the EFI to handle the situation so if it isn't going over the number of memory ranks the memory controller can access at 1066MHz then it won't downclock. On other boards the limit appears to be 12 ranks at 1066MHz. Either 3xQR or 6xDR. They likely set it in the BIOS that using QR and DR together drops it to 800MHz. 2xQR and 2xDR of course is 12 ranks total on a Mac Pro.
     
  23. Daud macrumors regular

    Joined:
    Oct 23, 2008
    #23
    Low cost options for 2009 2.66 Nehalem Quad

    Before getting this MP, I am trying to estimate the immediate additional cost and one of course is memory, as it "boasts" meager 3GB (3x1GB).

    Based of the info above, if I get the original memory (e.g. from somebody upgrading), then having 4x1GB, the clock speed will be maintained but the memory will be accessed on two channels only, correct ?

    Or, I can remove 1 stick and get two 3GB ones, for an arrangement
    2x1 and 2x3 for a total of 8GB. Not certain whether this would impair
    something..
    (8GB should be enough for me)
     
  24. Umbongo macrumors 601

    Umbongo

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    #24
    You can't get 3GB DIMMs.

    If you are only mixing 1GB and 2GB DIMMs that are branded for use with the Mac Pro then you will have no issues really, mix and match as much as you want.
     
  25. MacMolly macrumors newbie

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    SF BAY area
    #25
    Great Explanation

    I want to say thank you for posting such a clear and concise explanation for WHY this is happening and how to avoid it in the future. I've posted to other forums and NOBODY has come even close to explaining or even suggesting the "12" Rank maximum to maintain full bandwith. What this means to me next time I buy memory is that I'll need to know the "RANK" of the memory in order to be sure I can get optimal bandwith.

    Kudos, sir! I really appreciate it!
     

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