Memory asymmetry in Mac Pro

Posted:
in Future Apple Hardware
I am not sure how RAM memory is allocated on the new Mac Pro given all the memory combinations.
One question I do have is ~
If you place six 64GB DIMMs, and then add two 4 GB DIMMs (that were left over when you upgraded an iMac) -
Will this combination create a bottleneck of some type?  
Thanks for any guidance.  

Comments

  • Reply 1 of 6
    Mike WuertheleMike Wuerthele Posts: 6,273administrator
    Don't know yet. There will be some kind of matching required.
    OkiRun
  • Reply 2 of 6
    Don't know yet. There will be some kind of matching required.
    Thank you.  
    How would Apple communicate such information (i.e. the effect of staggering RAM cards on performance) ~  32GB, 8GB, 32GB, 8GB, etc....
    Not that this is how you want to do it... but generally speaking...
    I'm learning a lot and appreciate this site very much.
  • Reply 3 of 6
    https://www.youtube.com/watch?time_continue=231&v=-D8fhsXqq4o

    I found this Linus Tech video about RAM and configuration.  The upshot is that it does seem to matter, on the plus side, to chose RAM chips that are of the same make and size.  Using an asymmetric pattern seems to cause a default to the lowest MB size initially when RAM is utilized thereby under-utilizing the largest size chips initially.  Linus didn't produce any benchmarks about this, however, he seems to argue from a pragmatic point of view.  
  • Reply 4 of 6
    OkiRun said:
    I am not sure how RAM memory is allocated on the new Mac Pro given all the memory combinations.
    One question I do have is ~
    If you place six 64GB DIMMs, and then add two 4 GB DIMMs (that were left over when you upgraded an iMac) -
    Will this combination create a bottleneck of some type?  
    Thanks for any guidance.  
    Mike's answer of "don't know yet" is the correct one, but there are a few things we do know:

    You won't able to do what you suggest here. Standard 27" iMacs don't support ECC and use SO-DIMMs, which are different from those used on the iMac Pro and the new Mac Pro. The iMac Pro uses 2666MHz DDR4 PC4-21300. It can use either RDIMM or LRDIMM, but they cannot be combined. The system will not function with a mixed configuration. For maximum performance, population of all 4 DIMM slots is recommended. [https://eshop.macsales.com/shop/memory/imac-pro-2017]

    It might be possible if you are talking about about leftovers from an iMac Pro upgrade and you have the 8-core (Xeon W-3223) Mac Pro. They both use "2666MHz DDR4 ECC" memory. But we can't be sure about the details, not yet. But even that seems unlikely. The iMac Pro uses a very different CPU socket and chipset than the Mac Pro.

    Furthermore, the current iMac Pro (2017) is last-generation for its tier of Xeon-W (2100 series). It has not been refreshed to the current generation (2200 series). In an ideal world, the refresh would be the same day the Mac Pro is released. Then, going forward, both the Mac Pro and iMac Pro would be refreshed at the same time. But Apple does not have a good track record in this regard, for whatever reasons, as endlessly speculated and complained about around here. We'll see...

    All other Mac Pro processors, from the 12-core (Xeon W-3235) to the 28-core (Xeon W-3275M), use 2933MHz DDR4 ECC. But again, the precise details are not known. We do know that if you want more than 1TB RAM, you'll need the 24-core (Xeon W-3265M) or 28-core "M" CPU machines. 

    We also know that the Mac Pro has twelve RAM slots, in two banks of 3 x 2. All the configurations Apple sells are evenly distributed over four, six, or twelve slots. They don't offer 256GB DIMMs, but it is very likely that they will support them.
    edited November 2019 OkiRun
  • Reply 5 of 6
    OkiRun said:
    I am not sure how RAM memory is allocated on the new Mac Pro given all the memory combinations.
    One question I do have is ~
    If you place six 64GB DIMMs, and then add two 4 GB DIMMs (that were left over when you upgraded an iMac) -
    Will this combination create a bottleneck of some type?  
    Thanks for any guidance.  
    Mike's answer of "don't know yet" is the correct one, but there are a few things we do know:

    You won't able to do what you suggest here. Standard 27" iMacs don't support ECC and use SO-DIMMs, which are different from those used on the iMac Pro and the new Mac Pro. The iMac Pro uses 2666MHz DDR4 PC4-21300. It can use either RDIMM or LRDIMM, but they cannot be combined. The system will not function with a mixed configuration. For maximum performance, population of all 4 DIMM slots is recommended. [https://eshop.macsales.com/shop/memory/imac-pro-2017]

    It might be possible if you are talking about about leftovers from an iMac Pro upgrade and you have the 8-core (Xeon W-3223) Mac Pro. They both use "2666MHz DDR4 ECC" memory. But we can't be sure about the details, not yet. But even that seems unlikely. The iMac Pro uses a very different CPU socket and chipset than the Mac Pro.

    Furthermore, the current iMac Pro (2017) is last-generation for its tier of Xeon-W (2100 series). It has not been refreshed to the current generation (2200 series). In an ideal world, the refresh would be the same day the Mac Pro is released. Then, going forward, both the Mac Pro and iMac Pro would be refreshed at the same time. But Apple does not have a good track record in this regard, for whatever reasons, as endlessly speculated and complained about around here. We'll see...

    All other Mac Pro processors, from the 12-core (Xeon W-3235) to the 28-core (Xeon W-3275M), use 2933MHz DDR4 ECC. But again, the precise details are not known. We do know that if you want more than 1TB RAM, you'll need the 24-core (Xeon W-3265M) or 28-core "M" CPU machines. 

    We also know that the Mac Pro has twelve RAM slots, in two banks of 3 x 2. All the configurations Apple sells are evenly distributed over four, six, or twelve slots. They don't offer 256GB DIMMs, but it is very likely that they will support them.

    It was very kind of you to explain this.  I learned a lot!  You are greatly appreciated.  
  • Reply 6 of 6
    Don't know yet. There will be some kind of matching required.
    Thank you.  
    How would Apple communicate such information (i.e. the effect of staggering RAM cards on performance) ~  32GB, 8GB, 32GB, 8GB, etc....
    Not that this is how you want to do it... but generally speaking.
    I'm learning a lot and appreciate this site very much.
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