Mac Pro ram configuration

Discussion in 'Mac Pro' started by shinji, Apr 22, 2007.

  1. macrumors 6502a

    shinji

    Joined:
    Mar 18, 2007
    #1
    Hi,

    I bought my Mac Pro from the Apple store, and it is setup like this:

    Riser A
    -------
    Slot 1: 512 mb DIMM
    Slot 2: 512 mb DIMM
    Slot 3: empty
    Slot 4: empty

    Riser B
    --------
    Slot 1: 512 mb DIMM
    Slot 2: 512 mb DIMM
    Slot 3: empty
    Slot 4: empty

    I want to add another 2x1 gb RAM. Can I just add it to Riser A on Slots 3 and 4? If I do that, will it mess up the memory bandwidth or anything like that? In other words...does the highest capacity RAM have to be in Slots 1 and 2 on any given riser?

    thanks
     
  2. macrumors 68000

    Joined:
    Aug 30, 2006
    Location:
    New England
    #2
    I had mine configured same as yours when I bought it, and I just added 2x1GB . For optimum performance, you should move the 512MB sticks on Riser A to Slots 3 & 4 and put your 2 1GB sticks in Slots 1 & 2.
     
  3. macrumors 6502a

    Redneck1089

    Joined:
    Jan 18, 2004
    #3
    I didn't think it mattered too much what order the ram sticks are in... :confused: :confused:
     
  4. macrumors 68000

    Joined:
    Aug 30, 2006
    Location:
    New England
    #4
    Hey, I'm just going by what the "experts" say. The common wisdom is that you should always put the larger sticks in the front of each riser. I haven't seen any benchmarks that show exactly how much is gained. What are you worried about -- moving/breaking the OEM sticks? They're not made of marzipan! :D
     
  5. macrumors regular

    Joined:
    Apr 16, 2007
    Location:
    LONDON, UK
    #5
    Certainly the pdf manual doesn't metion specific slots for specific capacity chips. Though I suppose that's not to say it doesn't matter. They only specify the order in which chip pairs of any capacity should be installed
     
  6. thread starter macrumors 6502a

    shinji

    Joined:
    Mar 18, 2007
    #6
    Ok cool...where did you buy the 2x1 gb from? I was probably going to buy Crucial.
     
  7. macrumors 68000

    Joined:
    Aug 30, 2006
    Location:
    New England
    #7
    I got Techworks RAM from OWC last week for $220. Techworks is a memory module manufacturer, OWC brand is just a no-name they resell (there seems to be a fair amount of problems with the OWC branded memory, though OWC is good about replacing bad RAM). I didn't go with Crucial only because Crucial was charging $270. They have since dropped the price. I say go with Crucial, although Techworks will save you a few bucks. My Techworks RAM is working just fine. It runs about 15-20 F hotter than the OEM modules, but that may be because these are higher density sticks. The heat sinks on the Techworks are identical to the ones on the Apple OEM modules.
     
  8. macrumors G5

    gnasher729

    Joined:
    Nov 25, 2005
    #8
    First, whatever you do, it does make some difference, but not very much. The most important thing is to have as much RAM as possible, everything else is secondary.

    Now there are two principles: 1. The MacPro can read from both risers at the same time. This makes it fastest if you have the same amount of RAM in both risers, because that maximises the chance that they are both used at the same time. 2. The front two slots are a bit faster than the back.

    With this in mind, the best configuration would be 2x1GB in riser A, and 4x0.5GB in riser B. But it doesn't really make very much difference.
     
  9. macrumors regular

    Joined:
    Nov 16, 2005
    Location:
    Toronto, Ontario
    #9
    I don't see the Techworks RAM on the page, all I see are the OWC brand and the Netlist?
     
  10. macrumors 68000

    Joined:
    Aug 30, 2006
    Location:
    New England
    #10
  11. macrumors regular

    Joined:
    Nov 16, 2005
    Location:
    Toronto, Ontario
  12. macrumors regular

    Joined:
    Nov 16, 2005
    Location:
    Toronto, Ontario
  13. macrumors 68000

    Joined:
    Aug 30, 2006
    Location:
    New England
    #13
    Not much, but from what I remember reading while I was doing research before my own purchase they seem to have a solid reputation. A lot of people mention them and Crucial "in the same breath". However, seeing that Crucial is actually less expensive than Transintl now, I'd go with Crucial.
     
  14. macrumors 6502

    Joined:
    Mar 25, 2004
    #14
    What the "experts" say about ram configuration

    I have the same configuration as you. I've been looking into this issue myself, and have gotten all tied up in knots about the best way to upgrade. I had originally decided to add 4x512 chips, for a total of 8 fb-dimms for a total of 4 megs of ram. However, I'm not sure if that is optimal, based on articles from anandtech.com (here and here) and diglloyd.com (here). It seems as if the "best" configuration to get to 4 gigabytes of ram is 4 dual rank fb-dimms, split between both risers. The reasons appear to be:

    1. installing the memory in dual matched pairs (4 identical chips) lets the memory operate in quad-channel mode.
    2. dual rank dimms provide higher performance than single rank dimms
    3. having extra fb-dimms introduces some latency, so that the best trade off between bandwith and latency is with four chips.

    There is also a "rule of thumb" that you need 1 gig of ram for each processor. However, I have never seen any information that supports this theory.

    The problem with all of this is it doubles the cost of getting to 4 gigs, which is all I originally thought was necessary.

    I realize that this confuses the matter somewhat, and is inconsistent to the very practical advice provided by akadmon.
     

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