Mac Pro 3.1: Need help with RAM options

Discussion in 'Mac Pro' started by DIY_glenn, Sep 23, 2015.

  1. DIY_glenn macrumors member

    Sep 7, 2015
    My 2008 Mac Pro 3.1 w/2x3.2Ghz now has 2x4GB kingston and 2x1GB (stock) for a total of 10GB.
    The next step is to buy 4x4GB (eBay-version with heatsink), and probably remove the two 1GB so I have a total of 6x4GB.
    Or also remove the old Kingston ones for 4x4GB similar ones. I'll probably never need more than 16GB on this machine anyways (Logic Pro/FCPX mostly). I think buying 2 kits for 32GB is a bit overkill when I could get up to 24GB with the 2x4GB Kingston modules I already have + the eBay kit.
    Could the 1GB ones stay in as well for 26GB?... :)

    My instinct tells me that Kingston/eBay (Micron or Samsung chips) mixed together won't be a problem at all. AFAIK the modules has to be installed in pairs, and I reckon that the best performance would happen if they all are the same (4GB) size modules. But after all, it's been running with the current setup for years and years.

    What are your opinions?

    My options are:

    - 16GB: 4x4GB eBay RAM
    - 24GB: 6x4GB (4x eBay RAM + 2x Kingston RAM)
    - 26GB: 6x4GB + 2x1GB (4x eBay RAM + 2x Kingston RAM + 2x "Apple" 1GB)

    (And 32GB, but that would involve buying 2x 16GB kits, which means $240 instead of $120 for the kits... And I probably don't need half of the RAM anyways)

    As i mentioned, I'm probably good with 16GB, but who can ever have enough RAM?
    The Kingstons (B1/2 memory modules) reach a temperature up to 80C on load, the other two are 60-70C max.
  2. nigelbb macrumors 65816

    Dec 22, 2012
    The 800MHz FB-DIMMs were AFAIK only used by Apple so are relatively expensive. Much better value are the 667MHz parts that can be found really cheaply used as pulls from HP & Dell Xeon servers. The large Apple heat sinks are not required as the RAM runs cooler. Barefeats benchmarked 667MHz FB-DIMMs at just 4% slower than 800MHz but in real life the difference is not noticeable & in fact having a full 32GB of matched parts will likely make the system faster than an assortment of various capacity parts. Here is a full 32GB (8x4GB) for less than $50. You may even be able to recoup some of the $50 by selling the 800MHz parts you have to a Mac pro wner who still thinks they absolutely must have the higher speed memory sticks.
  3. DIY_glenn thread starter macrumors member

    Sep 7, 2015
    True, but with shipping here I'm probably gonna spend more than the 800mhz ones, so I'm trying to work out what's the best option with what I got + other memory brands together. Of course that would be 32GB with all similar, but I'd pay approximately $150 for it, compared to $110-120 for the 16GB ones.

    16GB is enough for me, I'm just wondering what the difference would be if I also put in the 8GB I have, and maybe also the 2GB for a total of 26GB.

    26GB > 16GB, is that all I need to worry about? Or will the speed/stability be affected?
  4. orph macrumors 68000


    Dec 12, 2005
    I use the slower 667MHz ram with apple heat sinks in my 3.1, mixed brands (not shore how to tell what brand they are).
    I have 18 GB of 2x1GB, 4X2GB, 2X4GB. I get 80-84C from some sticks according to hardware monitor.
    dont see why you need to pull the 1GB sticks if they work with the new ram, you will get a bigger slowdown from from going past your installed ram than non matched ram.
  5. UniversalWolf macrumors newbie


    Jul 16, 2008
    From what I've read, the tests seem to indicate that filling all the slots on your riser cards with the same type of DIMMs gives you a significant speed increase. Along the lines of 17%. That's why going for 8 4GB DIMMs of the 667 PC server RAM is an excellent option. 17% minus the 4% difference between the 800s and the 667s still leaves you with a 13% speed increase. I just did this in my 3,1 (starting from 6GB) and I noticed the improvement immediately. Of course my old DIMMs were 7 1/2 years old, so that may have been part of the reason for the increase too.

    Shipping costs may be a factor for you, but the 800 RAM is MUCH more expensive than the 667. People have piles and piles of unused 667 DIMMs for sale on eBay.
  6. nigelbb macrumors 65816

    Dec 22, 2012
    I don't know where the OP is based but I am sure that you can find loads of the 667MHz FB-DIMMs on your local eBay. The Apple heat sinks aren't necessary for these.

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