nMP Ram confusion

Discussion in 'Mac Pro' started by AndyUnderscoreR, Apr 26, 2014.

  1. AndyUnderscoreR macrumors regular

    AndyUnderscoreR

    Joined:
    Jul 11, 2008
    #1
    I'm planing on getting a 32Gb 6-core, but avoiding the Apple Ram tax by buying it with as little Tam as possible, ditching the stock Ram and buying more from a third party, so I need to understand what's going on with nMP Ram. Do we have definitive 'I've got one and tried it and it works' answers for these questions?

    1) If you build to order a 4 core with exactly the same spec as a 6-core, do you get exactly the same machine as if you ordered a 6? I know this sounds pointless at first glance, but it would unlock the option of a 12Gb 6-core, which Apple won't let you have if you start with the 6-core spec. This would save me money and meant I would be throwing away less Ram.

    2) Is there a speed penalty for not filling all the ram sockets? I could get my 32Gb as 4x8 and fill all the slots, or as 2x16 with room to buy another two and expand to 64 later.

    3) What's the deal with the 64Gb using different Ram? Is this stuff any faster or slower?

    4) I know you can't mix registered and unbuffered, but does this really prevent me ordering a 12Gb machine, taking out 1 of the three sticks and putting in two 16s for a total of 40Gb in the future when 32Gb unbuffered sticks are available?

    5) How about buying a 12, throwing out 1 stick and adding two 8s for a total of 24?
     
  2. Radiating macrumors 65816

    Joined:
    Dec 29, 2011
    #2
    There is no difference

    The penalty is your ram speed is halved with 2x16gb, which may be noticeable


    64gb doesn't use different ram than other large capacities, unless you mean unbuffered but macs from a software perspective don't like mixing 16gb or 32gb dims with any other sizes so keep that in mind.

    You won't be able to do that because again macs don't like mixing ram sizes of 16gb or 32gb and other sizes

    You'd be running at 8gb/s ram speed if you do that vs 60gb/s with 4 16gb dimms.
     
  3. AndyUnderscoreR thread starter macrumors regular

    AndyUnderscoreR

    Joined:
    Jul 11, 2008
    #3
    Thanks for the long and detailed reply! So this means a 12Gb 4-core will be slower than a 16Gb 4-core?

    The Apple store says "Mac Pro uses unregistered DIMMs (U-DIMMs) in all memory configurations except 64GB, which uses four 16GB registered DIMMs (R-DIMMs)." - I'm trying to understand what the difference is practically - should I be waiting for aftermarket unregistered 16Gb sticks to appear, for example?

    Now I'm even more confused. I can't mix 4s and 16s, but I could mix 4s and 8s, but with a 54 gb/s speed penalty? Where does that nearly 85% speed reduction come from?
     
  4. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #4
    You wouldn't notice the bandwidth difference between 3 and 4 DIMMs, just the capacity.

    No, because it looks like only one (small) company is going to make 16GB unbufferd DIMMs, they have a projected price of twice the amount of an RDIMM and are still in the sampling phase.

    http://www.intelligentmemory.com/dram-modules/ddr3-dimm/

    Using mixed DIMM capacities means you are limited to single channel performance.

    For the most part none of this matters as the minimum bandwidth you get with odd combinations won't hamper most people's work flow.

    If you are concerned then go with 2-4 DIMMs of the same capacity for optimal performance.
     
  5. AndyUnderscoreR thread starter macrumors regular

    AndyUnderscoreR

    Joined:
    Jul 11, 2008
    #5
    This is why things get confusing... I have one reply that says I can only mix certain different stick sizes, and will get an 85% speed drop if I do, and another that says the difference won't be noticeable! Has anyone actually tried this and benchmarked the results?

    I asked a question about registered vs unregistered. and I get a reply talking about unbuffered? Do they mean the same thing??

    If unbuffered DIMMS are more expensive (which sounds wrong, surely adding a buffer means more components?) surely that means they are in some way better?
     
  6. shaunp macrumors 65816

    Joined:
    Nov 5, 2010
    #6
    My requirements are similar to yours, I want the 6-core but with 64GB RAM. As I don't intend on using the Apple RAM I bought the least amount I could by configuring the base 4-core that comes with 12GB, and upgrading the CPU to 6-core. I can then swap out the 12GB for 64GB from Crucial. It works out around £80 cheaper to do it this way.
     
  7. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #7
    There are benchmarks on the internet yes. You will hear large numbers when people are looking at the possible peak bandwidth differences. 4 DIMMs can push 4 times the bandwidth of one, so obviously that is a big difference.

    Real world application performance for the vast majority of users will not be impacted by huge variances in potential bandwidth. Look a this page and you can see barely any difference between single and dual channel for the actual applications. Not something to be ignored when trying to achieve maximum performance, but not something to be hugely concerned about either if temporarily trying some other configuration for budget reasons.

    http://www.gamersnexus.net/guides/1349-ram-how-dual-channel-works-vs-single-channel/Page-3?showall=

    Most RAM is unbuffered: laptops, desktops, gaming computers, phones, tablets, graphics cards etc. Just means the memory has nothing between it and the memory controllers. When using large amounts of memory more electrical load is placed on components and a memory register can ease this load by storing data in the register for a clock-cycle. That's a pretty simple explanation so you might want to wiki Registered Memory.

    That company is the only one making them and it's for a tiny potential customer base as they don't offer anything to most customers and they are using an obscure technique to get unbuffered 16GB DIMMs. That's why they are more expensive. The big vendors aren't bothering to make unbuffered DDR3 16GB DIMMs. Expect DDR4 16GB unbuffered DIMMs though.
     
  8. AndyUnderscoreR thread starter macrumors regular

    AndyUnderscoreR

    Joined:
    Jul 11, 2008
    #8
    Thanks, it's good to know that someone from the UK has successfully gone down this route before me. Did you find any use for the Apple 12Gb you have spare? I've not seen anyone over here offering a rebate for them.
     
  9. AidenShaw macrumors P6

    AidenShaw

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    Location:
    The Peninsula
    #9
    Some hard data

    Take a look at http://forums.macrumors.com/showthread.php?t=1704700 - this shows that most benchmarks see little or no difference between various memory configs.

    The Xeons have huge caches which typically mean that theoretical raw memory bandwidth is not that important for most apps.
     
  10. Radiating macrumors 65816

    Joined:
    Dec 29, 2011
    #10
    Mac's do not like to mix 16gb and 32gb dims with any other sizes. This is just something weird that applies to Macs, but in no other scenario, so you can mix ram sizes with systems that do not have bugged configurations like the Mac Pro.

    These results are based on mathematically sound performance figures. You will see an 85% performance drop, but it's all relative, you may not need 90% of the performance ram offers. Most programs cannot take advantage of incredibly fast ram speeds.

    It's more complex that that.
     
  11. VirtualRain macrumors 603

    VirtualRain

    Joined:
    Aug 1, 2008
    Location:
    Vancouver, BC
    #11
    Just buy the 32GB from Apple. You won't save much doing it yourself. The tax (on the 32GB upgrade) is minimal and not worth the time/hassle because to maximize the benefit, you need to sell the sticks you remove... Just not worth it IMHO.
     
  12. AndyUnderscoreR thread starter macrumors regular

    AndyUnderscoreR

    Joined:
    Jul 11, 2008
    #12
    The cost to upgrade from 12 to 32Gb by buying memory from Crucial is £269.99. Requires 10 minutes installation time and means throwing 12Gb away.

    The cost to upgrade from 12 to 32Gb by buying more BTO memory from Apple is £400... and because Apple give you 4 sticks of 8Gb not two of 16Gb, you can't upgrade to 64 without throwing 32Gb away.

    So I'd be getting a more flexible setup and saving £130.01, even if I don't sell the spare 12Gb - that's hardly a minimal saving for 10 minutes work!

    ----------

    32gb dims? As far as I know these would only make sense as part of a 128Gb setup.

    I can't find any evidence at all to back up these claims, can you show me these "mathematically sound performance figures" please?

    Can you explain it then?
     
  13. shaunp macrumors 65816

    Joined:
    Nov 5, 2010
    #13
    I've not received it yet, I only put my order in for the nMP a few days ago. However I plan on just hanging onto the memory for warranty purposes. Yes Apple are okay with you swapping out the RAM, but if there is ever an issue I'll put the original RAM back in then there's no finger pointing. Besides you wouldn't get that much on ebay for it anyway. It just seems more hassle than it's worth to sell it.
     
  14. Jim-H macrumors member

    Joined:
    Dec 31, 2013
    #14
    For the upgrade price of 32GB of Apple ram you could almost get 64GB from a 3rd party.
     
  15. jenzjen macrumors 68000

    Joined:
    Aug 20, 2010
    #15
    true internet recovery will not work if you switch your ram so make sure to create a mavericks usb installer should the need arise
     
  16. AidenShaw, Apr 27, 2014
    Last edited: Apr 27, 2014

    AidenShaw macrumors P6

    AidenShaw

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    #16
    It's not an Apple thing - the Xeon E5 processors do not support mixing UDIMMs and RDIMMs and LRDIMMs in any system or combination.

    Apple's small DIMMs are UDIMMs, all of the 16GiB DIMMs are RDIMMs and the 32GiB DIMMs are RDIMMs or LRDIMMs. And the 4-core, 6-core and 8-core Apples don't support LRDIMMs. (The 8-core E5-1680v2 that Apple was using is no longer listed at http://ark.intel.com/products/family/78582/Intel-Xeon-Processor-E5-v2-Family#@Server - maybe the Rev.B Tube will be sooner than expected.)
     
  17. Umbongo macrumors 601

    Umbongo

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    Sep 14, 2006
    Location:
    England
    #17
  18. psycho bob macrumors 6502a

    psycho bob

    Joined:
    Oct 25, 2003
    Location:
    Leeds, England
    #18
    Internet recovery worked fine for me straight after I swapped to Crucial memory. No reason it shouldn't it is based on your App Store account usually and nothing more. I have a feeling restoring to the preinstalled OS (ie what it shipped with) doesn't even check the app store (a good chance the user may not have purchased/downloaded the OS if this is their only mac).
     
  19. Riwam macrumors 6502a

    Riwam

    Joined:
    Jan 7, 2014
    Location:
    Basel, Switzerland
    #19
    Wise decision

    ...................,
    I find ot very wise.
    I intend as well to keep my 3 x 4 GB just in case a repair might be needed.
    It is truly not worth to try to sell them when upgrading the RAM by oneself...
    :)
     
  20. jenzjen macrumors 68000

    Joined:
    Aug 20, 2010
    #20
    Psycho b

    Did you see the a spinning earth icon? If not, that was recovery off the HD which the vast majority of times is where you go when you hit recovery, to force internet hold down command option r instead of just command r
     

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