New Mac Pro slower with extra memory. Why?

Discussion in 'Mac Pro' started by mattmac, Feb 1, 2008.

  1. mattmac macrumors newbie

    Jan 9, 2008
    Got my new Mac Pro 2.8 octo with standard 2GB memory last week and its brilliant. Really pleased.

    Just put in 4 x 2GB memory from OWC (slots 1,2 top card and slots 1,2 bottom card) and it is now slower when I use my 3D app Strata CX 5.5. Strata is a 32 bit app so it has a 4GB limit, but when doing a test render activity monitor shows only 350-400MB real memory being used and a whopping 1.4 GB virtual memory being used.

    Does anybody have any ideas as to why the real memory isn't being used instead of the slower virtual memory. Is it the app or the OS that controls this?

    I wasn't expecting massive gains in render speed, (it's quick enough as it is), but its an expensive way to slow your machine down.

    I have been advised that the more memory you put in the larger the OS overhead, is this the case?

    I am hoping the 10.5.2 update might help but I'm not hopeful. Is anyone else finding their machines slowing down?:confused:
  2. Masher500 macrumors member


    Sep 12, 2006
    Dana Point
    Take your 1gb sticks out and sell them.. Put that money in the piggy bank, and save for an extra 4gb. Its the 1gb dimms that are slowing your mac down.

    Thats of course if i understand your set up correctly..
  3. mattmac thread starter macrumors newbie

    Jan 9, 2008
    The 1GB sticks aren't in there. 2 x 2GB top card and 2 x 2GB bottom card, 8GB total. A couple of other threads have mentioned to leave out the stock memory because its unbalanced if you fill 6 slots instead of 4 or all 8. I just hope when I buy another 8GB it doesn't slow down even more !!!!
  4. digitalnicotine macrumors 65816


    Jan 11, 2008
  5. ErikAndre macrumors 6502a


    Nov 14, 2007
    I found this thread particularly helpful. It suggests alternate configurations of which slots to place the ram in. Not sure if it will help you, but I'm in the same boat and may sell my stock 2gb ram if it poses a similar problem.
  6. mattmac thread starter macrumors newbie

    Jan 9, 2008
    Memory purchased is OWC Mac Pro Qualified.

    Just talked to Apple Tech Support and they are puzzled and have asked me to try different memory configurations to see it changes anything.
  7. aibo macrumors 6502

    Jan 17, 2008
    Southern California
    can you post some benchmarks (or memory test benchmarks) for before and after?
  8. phjo macrumors regular

    Jan 8, 2008
    Your mac pro definitely shouldn't be slower with such a configuration... The opposite should of course be expected so something weird is happening there (do an apple hardware test maybe ?)

    But as concerns virtual memory, it is just, as it is called, <<virtual>> in the sense that the ram above the real ram is not really allocated... yet. It is certainly not memory that get swapped to the harddrive.

    Why does leopard reserve such a huge amount of virtual memory for processes, I have no idea, and am not so happy about it, as a 32 bit application can't use as much memory as it could with tiger, but you have to look elsewhere for the slow performance you're complaining about...

  9. Peace macrumors Core


    Apr 1, 2005
    Space--The ONLY Frontier
    The way the new MP works with memory is different than the old MP

    When Apple says put in 2 sticks at a time they mean.

    For example..You buy 2 2gig sticks

    One stick goes in the top riser and one goes in the bottom riser.

    Same is true if you buy 4 sticks.Two in the top and two in the bottom.
  10. phjo macrumors regular

    Jan 8, 2008
    Well, I think the OP made it clear he did it by the book, with two dimms on slot 1 and 2 on each riser...

  11. Jonny427 macrumors regular

    Oct 16, 2007
    Orange County, CA
    Yes he installed it correctly.. I have no idea what the problem is.
  12. phjo macrumors regular

    Jan 8, 2008
    Maybe there is no problem... except that maybe the OP saw this vm column in activity monitor and started to wonder and feel that his mac pro is now slower...

    With no benchmark to come with it, it is difficult to be sure...

  13. Picasosz macrumors newbie

    Jan 12, 2008
    I've got 6gb 2x1 and 2x2

    I have not noticed any slow down using the stock 2GB and added 4GB
  14. mattmac thread starter macrumors newbie

    Jan 9, 2008
    Okay, just finished some test renderings, so here are the figures.

    The software I am using is Strata CX 5.5, a 3d modeling and render package similar to C4D, Lightwave and Maya etc. I am rendering a single frame image of a large restaurant with about 75 light sources. There are no start up items and Strata is the only app running apart from activity monitor to check memory and CPU usage. Memory as I mentioned before is OWC qualified.

    Render 1
    Stock 2 x 1GB (Apple)
    Slot 1 top card
    Slot 1 bottom card
    Real memory used 1.7GB
    Time - 1h 35m 5 s

    Render 2
    2 x 2GB slots 1 & 2 top card (OWC)
    2 x 2GB slots 1 & 2 bottom card (OWC)
    Real memory used 2.43GB
    Time - 1h 31m 56s

    Render 3
    2 x 2GB, slots 1 & 2 top card (OWC)
    2 x 2GB, slots 1 & 2 bottom card (OWC)
    2 x 1GB, slots 3 & 4 top card (Apple)
    Time - 1h 31m 46s

    It seems that if I do a more simple render there is an actual slowdown with the greater amount of memory installed ie 10m 39s instead of 10m 25s. Once you start to push the machine it does slightly better, but I don't consider a saving of 3/4 mins on a 90min render impressive.

    The only thing I have noticed is that running other apps such as Safari or Camino with Strata in the back ground don't seem to suffer and are just as snappy as if they were running on there own.

    If I do any other times I'll publish them in this thread.
  15. Spikeanator6982 macrumors 6502

    Jun 13, 2007
    I would say that the program only needs ~2.5 GB ram so thats why you don't see much improvement going from 2 to 8. I would say that the ram isn't the bottleneck after you put over 4GB in the machine. And the snappyness of safari etc is bc the applications dont have to fight for ram. So the ram is doing good.

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