Question about RAM placement

Discussion in 'Mac Pro' started by IKEA, Nov 26, 2007.

  1. IKEA macrumors newbie

    Joined:
    Aug 23, 2005
    #1
    So… in a week or two I'll hopefully receive my newly ordered BTO 4-core mac pro. (I'd have waited for Penryn, but I absolutely can't. :()

    In addition to the stock 2x512MB sticks, I've ordered 4x1GB of the Netlist RAM from OWC, which will probably end up arriving some time before the actual Mac Pro.

    Now, I've read up on the general RAM placement guidelines (matched pairs always together, etc.), but I'm still wondering whether I should take out the stock RAM or leave it in for a total of 5GB. I've read posts saying that having the smaller RAM sticks in there will actually slow down performance. Is this true? Which RAM placement will get me the best performance?
    Also, if I do leave the stock RAM in, where would people recommend I put it? The options are either together with two 1GB sticks (i.e. Riser A: 512/512/1024/1024, Riser B: 1024/1024) or on a separate riser with all the 1GB sticks together on the same riser.

    Help appreciated.
    Cheers,
    -ikea
     
  2. scottious macrumors newbie

    Joined:
    Nov 26, 2007
    #2
    This is a good question because I'm am actually doing the very same thing soon. My first guess was to just leave out the 2x512 modules because I heard somewhere that it's better to have 2 or 4 slots filled in rather than 1 or 3 from a performance point of view. I wish I could say for sure, but I guess some benchmarking with 4gb vs 5gb using xbench might yield some relevant results.
     
  3. bigbird macrumors 6502

    Joined:
    Aug 17, 2007
    Location:
    Canada
    #3
    Here's the suggestion from the experts:

    Riser A: 1GB - 1GB - 512MB - 512MB
    Riser B: 1GB - 1GB
     
  4. JesterJJZ macrumors 68020

    JesterJJZ

    Joined:
    Jul 21, 2004
    #4
    So larger pairs first on both risers...
     
  5. CanadaRAM macrumors G5

    CanadaRAM

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    Oct 11, 2004
    Location:
    On the Left Coast - Victoria BC Canada
    #5
    Yes. The #3 and #4 slots are slower (higher latency) so concentrate the most RAM in the 1 and 2 slots.
     
  6. termina3 macrumors 65816

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    Jul 16, 2007
    Location:
    TX
    #6
    This is where multimedia would post his table; did they take all of his posts down as well?
     
  7. rockinrocker macrumors 65816

    rockinrocker

    Joined:
    Aug 21, 2006
    #7
    i think i have a screen shot of it somewhere, i'll see if i can dig it up in a minute.
     
  8. rockinrocker macrumors 65816

    rockinrocker

    Joined:
    Aug 21, 2006
    #8
    here it is.....
     

    Attached Files:

  9. IKEA thread starter macrumors newbie

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    Aug 23, 2005
    #9
    That's awesome. Thanks.
    Riser A's the top riser, yeah?
     
  10. iSavant macrumors regular

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    Mar 31, 2007
    Location:
    Colorado
    #10
    Yes
     
  11. vuelta macrumors newbie

    Joined:
    Feb 3, 2009
    #11
    so just to be certain....my Mac Pro came with four 512MB sticks, two in riser A and two in riser B. I just bought two 2 GB sticks and installed as follows:
    Riser A: pair of 2 GB, pair of 512 MB
    Riser B: pair of 512 MB

    Looking at the schematic, it appears that I should have done the following:
    Riser A: Pair of 2 GB,
    Riser B: Pair of 512MB, Pair of 512 MB

    Is this correct? If so, why?
     
  12. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #12
    It is to do with memory bandwidth. You get maximum bandwidth (quad channel/256 bit) when memory is accessed from both risers. With both pairs of 512MB memory on riser B this means you can access a total of 4GB of memory at full bandwidth (2GB from each riser), and a further 2GB at half bandwidth. With how you currently have it you would access 2GB at full bandwidth and 4GB at half bandwidth.
     
  13. vuelta macrumors newbie

    Joined:
    Feb 3, 2009
    #13
    I switched to the memory confirmation as noted above: two 2 GB sticks on Riser A (the upper one) and four 512 MB sticks on Riser B (the lower one) and my Power Mac refused to start, just blinking the light above the on-off switch. I switched back to my previous setup: two 2GM and two 512 MB sticks on Riser A and two 512 Sticks on Riser B, and it works. Looking at the schematic on the inside of the Mac Pro case, my setup is recommended.

    Can you explain what happened. When I check "This Mac" setup, all is well regarding memory, ie 6 GB distributed on the appropriate Risers.

    What you saying is that only a full riser gives maximal bandwidth and a half full riser gives 1/2 bandwidth, so, with my present setup, I'm getting only 1/2 of my additional 4 GB memory and the full 4x 512 or 2GB on riser B, equalling 4 GB total.

    I want to maximize my speed. Do I need to buy two more 2GB sticks? Is there a problem with Riser B?

    I'm confused and a bit frustrated.

    Please advise.
     
  14. Umbongo macrumors 601

    Umbongo

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    Sep 14, 2006
    Location:
    England
    #14
    Ok, you will have 6GB no matter how you arrange them on the risers. It is the speed at whcih the memory interacts with the system that is affected by how they are placed. The chart posted is mostly theoretical I believe, so it doesn't actually mean that 2x2GB on A and 4x512MB on B will work.

    I wouldn't worry about it too much. Capacity will nearly always come before speed for most people's usage. 512MB DIMMs can drag down peformance due to being single ranked rater than dual as other DIMMs are and because of their small size. I can reccomend you go and get another 2x2GB and ditch the 512MB sticks, but you're then looking at another $100 and all it may end up giving you in reality is peace of mind.
     
  15. vuelta macrumors newbie

    Joined:
    Feb 3, 2009
    #15
    I appreciate your help. I will think about buying more RAM.

    I bought the Power Mac, my first Apple computer, because I was so frustrated with Windows issues. I wanted a powerful computer that would allow me to do whatever I wanted really fast. I was surprised when it bogged down at times. The Apple Store told me that the Power Mac requires a huge amount of RAM to function optimally and that my 512 x 4 was the problem.

    What is the optimal memory for top Power Mac (non-gaming, some photo and video editing) performance?

    Thanks.
     
  16. vuelta macrumors newbie

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    Feb 3, 2009
    #16
    Correction:

    In my previous post, I meant Mac Pro, not Power Mac.

    It's been a long day.
     
  17. Fomaphone macrumors regular

    Joined:
    Jan 11, 2009
    #17
    4gb is the recommended minimum for HD video editing. if you run photoshop while editing as many people do, don't go below 6.

    as far as "optimal" goes... max it out!
     
  18. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #18
    Some people say 1GB per core others 2GB per core. The issue stopped being discussed when the 2008 Mac Pros came out because OWC (I think) pushed Mac Pro memory so low that a lot of people just went and got 4x2GB kits.

    Apple always shipped workstations (G5 onwards at least) with the minimum amount of memory needed and let customers choose to add what they wanted. Apple don't want to be a memory vendor. The problem this causes is that there doesn't seem to be an offical stance on the issue. OSX does let you determine if you need more memory through the activity monitor, but it can be hard to judge the amount.

    http://macperformanceguide.com/index.html that site might be useful to you if you want to not just splash more memory. Also see how you get on with 6GB and monitor the activity, umm, monitor.
     
  19. Anonymous Freak macrumors 601

    Anonymous Freak

    Joined:
    Dec 12, 2002
    Location:
    Cascadia
    #19
    The Mac Pro already has the Xeon-equivalent of the Penryn. Per the Mac Pro Tech Specs, the current Mac Pro uses Xeon 5400-series procs, which are 45 nm, just like Penryn. (For the Xeons, the code-name for these chips is 'Harpertown'.) They have every benefit of Penryn on mobile; only they are the high-end dual-socket chips.
     

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