RAM in a Mac Pro, Quad Core Xeon, early 2009.

Discussion in 'Mac Pro' started by tsuki, Nov 16, 2009.

  1. tsuki macrumors newbie

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    #1
    Hey, I;ve searched a lot on this but don't seem to be getting any straight answers for myself so was hoping someone could iron out my queries.

    I've just ordered my Mac Pro (very excited) and intend on upgrading the RAM myself.

    OWC will cost too much with import tax, Crucial and Kingston seem costly too.

    Upon investigation, DDR3 1066Mhz Ram is not that common in terms of people that do it. It seems that Corsair, OCZ etc do good RAM, but is 1333Mhz and so not in Apples range as they are locked at 1066. These 1333 are the same price as 1066 or less sometimes.

    My question is: Even though they may remain locked at 1066, can I use 1333 in my Mac Pro? I intend to use Boot Camp for Windows 7 for gaming, so better RAM would improve that hopefully.

    I'm dropping an EVGA GTX 295 in too which should be pretty sweet :D

    Thank you.
     
  2. gugucom macrumors 68020

    gugucom

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    #2
    Apple use Hynix ECC UDIMMs at CL7 running 1066 MHz as you say. But 1333 memory of the same brand does it also. It just switches down in my experience.

    If you want to use maximum RAM capacity you can fill all four slots with 8 GB RDIMM sticks but bandwidth will drop considerably (33%) due to the fact you drop one memory channel from 3 to 2.

    Unfortunately Windows cannot use the faster RAM either. This is due to the EFI firmware locking the memory clock multiplier at 8 instead of 10.

    Here in Europe Google "Mihatsch Trading Ebay" for very good service and competitive pricing. They do custom designed kits for the 2009 Mac Pro. If you have made a mistake you can return everything within 2 weeks due to the remote sales or online sales law.
     
  3. tsuki thread starter macrumors newbie

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    #3
    Ah cheers for that man, will any brand of ECC registered 1333 do the job? There's just so much more choice at that clock speed.

    I'm guessing Apple have locked down that multiplier as hard as it can be locked down. No way to change?

    I have no need for that much RAM, I was considering either 6 or 8 gig. Am I right in reading that having three of the four slots filled rather than all four is better yes? Or is that only on the full 8GB sticks/

    Will check that website and see what it says.

    Thank you.
     
  4. nanofrog macrumors G4

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    #4
    Yes. UDIMM is usually cheaper though.

    Yes, its a fixed value in the firmware, and no way to change it. Perhaps someone will write a utility that allows users to re-writes the value, but I wouldn't bet on it. ;)

    Good luck. :)
     
  5. gugucom macrumors 68020

    gugucom

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    #5
    You have to either run UDIMMs or RDIMMs. Mixing will not work. Filling three Slots with the same sticks is the fastest but you can also use two pairs of rising capacity. Slot1 and Slot2 have an independent memory channel. Slot 3 and Slot 4 share the same memory channel. I give you a table.


    Slot1 Slot2 Slot3 Slot4 (Size in GB)
    2......2......2.......-
    2......2......1.......1
    4......4......4.......-
    4......4......2.......2

    The nice thing about using 2,2,1,1 is having to buy only 2x2GB. The next time round you only need to buy 2x4GB. If you use UDIMMs only and the same specification except for the capacity you can mix 1066 and 1333 of the Hynix sticks. It should work with other brands as well. But this is where it becomes an advantage to buy from a known vendor who gives you kits that have been tested and will take it back in case it doesn't work.
     
  6. nanofrog macrumors G4

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    #6
    UDIMM should be less expensive though, no matter the location (taxes, shipping,..).

    Unfortunately, keeping the same value (DIMM density), the OEM memory must be pulled. Otherwise it's only capable of adding a single 1GB UDIMM to make the capacity = 4GB. Too little for what tsuki wants.

    The idea of going with a 2x 4GB kit, followed by another is a very good idea if it must be spaced (identical kit to retain a unified type; UDIMM or RDIMM) over time to reach 8GB (budget reasons). :)
     
  7. tsuki thread starter macrumors newbie

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    #7
    I think going for 2 x 4GB is going to be the way I'm going to go. Good expandability without slowing the thing down by installing in all 4 slots. I can always get another 4GB module if I like.

    Now I've just got to decide which brand....
     
  8. gugucom macrumors 68020

    gugucom

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    #8
    If you just install 2 x 4GB you will pull down your bandwidth because you are only using 2 of your 3 memory channels. It will not matter for most apps but if you ever experience computing speed bottlenecks adding 2x 2GB might help.
     
  9. tsuki thread starter macrumors newbie

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    #9
    Wow Apple don't make it easy do they? A few years ago I remember building pc's and it was a whole lot easier doing that! OK... will make decisions about having either 2gb 2gb 2gb empty or 2gb 2gn 1gb 1gb. Perhaps the Kingston stuff from MacUpgrades.

    Thanks for all your help guys!
     
  10. gugucom macrumors 68020

    gugucom

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    #10
    You are right, Intel build a very power full system with triple memory channels. That would not be too bad if Apple had fitted all memory channels with two DIMM slots. But they fitted one DIMM to the first two channels and two to the third which makes little sense. Most users who look into the details criticize that and agree Apple should provide six DIMM slots (2 per memory channel) like most other manufacturers.
     
  11. tsuki thread starter macrumors newbie

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    #11
    Agreed. Sometimes I reckon that they just make in difficult to discourage anyone from detouring from the norm. I really like Apple in many ways but I don't agree with this forced homogenisation of computers.

    Ergo, I decided to be difficult and add an EVGA GTX 295 which they don't provide, and don't prepare for. I've got some guides which give reasonable walk through, although it's not cut and dry yet.

    I think I'm going to go for the 2 - 2 - 1 - 1 configuration. It means I can go up to 12 with a 2x4gb upgrade when I want. How much performance do you reckon I will lose by filling all four slots?
     
  12. Umbongo macrumors 601

    Umbongo

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    #12
    You lose like 30% of your bandwidth by using 4 slots instead of 3, less with RDIMMs. However this may have no impact on your usage.
     
  13. gugucom macrumors 68020

    gugucom

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    #13
    If you put half size DIMMs in the 3rd and 4th slot you do not loose any significant bandwidth. Only if you leave those slots empty you loose the third channel which means 33% bandwidth loss.

    The third channel has the two DIMM slots and uses the combined capacity of both. It means that all three channels will run in symmetry again.

    The beauty of that solution is the relatively cost efficient upgrade until you reach 4 GB density. Beyond 4 GB DIMM size you need to switch from UDIMM to RDIMM and you cannot mix.

    This means anybody who considers not using any 1 or 2 GB modules should definitely buy 4 GB RDIMMs. He can use them on the third channel and needs only 2 x 8GB modules if that upgrade occurrs.
     
  14. gugucom macrumors 68020

    gugucom

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    #14
    Not if he fits half size DIMMs on the 3rd memory channel.
     
  15. Umbongo macrumors 601

    Umbongo

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    #15
    Where are you getting this information from? Have you benchmarked this or something to get numbers that show it, because it isn't how the technology is documented.
     
  16. plong macrumors newbie

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    #16
    Echoing the common sentiment, this is so confusing! So there are 4 slots for RAM modules, but Apple only wants you to use three of them? Huh?

    I was searching the RAM sites when i stumbled across this:
    So if I were to buy 2 4GB sticks, to add to my 3 GB of factory RAM, will it work?

    Can I run 4 - 4 - 1 - 1?
     
  17. Umbongo macrumors 601

    Umbongo

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    #17
    You get the best performance in 3s. Apple only went with 4 slots per processors probably due to physical case size and the realworld performance differences being minimal for the majority of their intended customer's use.

    OWC had issues with this early on, I don't know if they still do. Maybe contact whoever you buy from first.
     
  18. gugucom macrumors 68020

    gugucom

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    #18
    First, it is logical if you consider the technology.

    Second, I did read up on the 5500 Intel tech stuff.

    Third, I did some Geekbench tests while I was having the modules here.

    Since then I have returned two DIMMS and so I could not run more memory related tests. But I asure you the band width difference between running 4 GB in one DIMM/channel and 4GB in two DIMMs/channel is single digit. You will not realize it under normal conditions.
     
  19. gugucom macrumors 68020

    gugucom

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    #19
    No that will not work well.

    2 - 2 - 1 - 1 will work.
    4 - 4 - 2 - 2 will work equally well.

    And always make sure you do not mix UDIMM with RDIMM. Particularly the 4GB sticks are available in both technologies at very similar prices. This may be the reason why certain kits do not mix.
     
  20. yg17 macrumors G5

    yg17

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    #20
    So, on a quad core Mac, is there any reason not to run 4x2GB sticks of RAM, filling up all the DIMM slots?
     
  21. gugucom macrumors 68020

    gugucom

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    #21
    Yes, you would be loosing bandwidth because the third channel would not be symmetrically populated. But the bandwidth would be still way beyond the 2008 RAM, which ran dual channel and 800 MHz.
     
  22. yg17 macrumors G5

    yg17

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    #22
    Ugh, this is so confusing. So it sounds like, for bandwidth purposes, I'm better off with 3x2 or 3x4?
     
  23. gugucom macrumors 68020

    gugucom

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    #23
    Yes, but for cost you would be better off with mixed modules mentioned in #19 for the same capacity. 2 GB DIMMs are better value/GB than 4 GB DIMMs.
     
  24. Umbongo macrumors 601

    Umbongo

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    #24
    I agree you won't notice the differences unless memory bandwidth poses a limitation which it does not for most things. And slower memory is better than less memory.

    In a Mac Pro you have:

    bank 0
    channel 1
    channel 2
    channel 3

    bank 1
    channel 1

    With all slots filled it should interleave (0:1 and 0:2) and (0:3 and 1:1) then interleave those two pair. You lose like 25% bandwidth rather than 33% because it isn't dual channel in the sense of just having DIMMs in 0:1 and 0:2. You see more lost on the benchmarks with UDIMMs due to having memory installed beyond bank 0 (RDIMMs don't have this problem). This is correlated by the memory bandwidth benchmarks that came out early on.

    What you seem to be suggesting is that when you install the same capacity on each channel (total) it interleaves 0:1 and 1:1 and then that pair with 0:2 and 0:3 to get triple channel. I agree logically this makes sense, but I've not seen it mentioned anywhere and I have to question if that were the case why it wouldn't happen with 4GB (2x2GB) on channel 1 as mixed capacity modules are supported. A link to where you determined this from would be great.

    What I do think might be helpful is if we were to compile some sort of list of the best configurations of memory modules in regards to the Mac Pro that can just be pasted in to threads of this kind. The problem wth RDIMMs is I don't know if any support the thermal sensor, though if you want the best performance/capacity it is soemthing that can probably be overlooked.

    As much as people complained about FB-DIMMs they sure were easier to understand.
     
  25. gugucom macrumors 68020

    gugucom

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    #25
    [​IMG]

    This picture should make it much clearer. Intel have foreseen 18 DIMM slots but I have covered those that are not used by Apple.

    For the quad just take away the right side of the picture. The DIMMs are numbered as in Apple's MP4,1 nomenclature. Memory channels are bottom 1 and top 3 on both CPUs. I have not labeled those to avoid confusion.

    Channel 3 runs the DIMMs 3and 4 respectively 7 and 8 on the second CPU.

    When you fill only two DIMMs your band width drops obviously because you miss one memory channel.
    When you fill all DIMMs your band width drops because asymmetric population of the three channels.
    When you fill three DIMMs your population is symmetrical and band width is best.
    When you fill two channels with same size DIMMs and the third channel with half size DIMMs your population is symmetrical again and band width is best. You may get 2-3 % less for registered DIMMs due to increased overhead, but fundamentally the mixed mode is almost full band width.
     

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