Reason to NOT keep stock ram?

Discussion in 'Mac Pro' started by mlankton, Apr 1, 2009.

  1. mlankton macrumors newbie

    mlankton

    Joined:
    Mar 30, 2009
    #1
    Getting a 2.8 octo delivered tomorrow. Have two 4gb kits for it (2x2gb each), and in a couple weeks I was going to order one more 4gb kit, for a total of 14 gigs, all slots filled including the stock 2 gigs.

    Is there a reason this is not a great configuration? Would one be better off using this 2x1, 6x2 setup, or would 6x2 perform better for some reason?

    I am getting conflicting info regarding the benefit of filling all slots vs having all fb-dimms be matched. I know in a perfect world I would just use 8x2 for 16 gb total, but my wife is not going to suffer me putting any more money into this box, so the two listed configs are my options, 14 (2x1, 6x2) or 12 (6x2) total.

    Appreciate your opinions.
     
  2. grue macrumors 65816

    Joined:
    Nov 14, 2003
    Location:
    Somewhere.
    #2
    In a 2008 model, filling all slots has a marked benefit.
     
  3. mlankton thread starter macrumors newbie

    mlankton

    Joined:
    Mar 30, 2009
    #3
    Ok, sold. Just ordered 4 more gigs (2x2) to fill all slots.

    Is it best to place the two single gig sticks in slots 1&2, or slots 7&8?

    Thanks again
     
  4. nicolasmasset macrumors regular

    Joined:
    May 25, 2007
    Location:
    Belgium
    #4
    Says who?
    I'm about to buy the same machine and thought about it too. But I really don't need more than 8gb. So 8x1 would be better than 2x1 + 3x2? I mean, benchmark wise, ok, perhaps you'd see some improvement but in real world usage, I can't really believe it would make such a huge difference.
     
  5. grue macrumors 65816

    Joined:
    Nov 14, 2003
    Location:
    Somewhere.
    #5
    http://www.barefeats.com/harper3.html
     
  6. nicolasmasset macrumors regular

    Joined:
    May 25, 2007
    Location:
    Belgium
    #6
    Thanks for the link!

    Just read it. A 15% speed increase, is that noticable? I work with audio by the way. Would that decrease the latency? If so I might just go with 8x1..
     
  7. mlankton thread starter macrumors newbie

    mlankton

    Joined:
    Mar 30, 2009
    #7
    You have to install fb-dimms in pairs, so you can't just jam singles in.

    For 8, using your stock ram, your options would be:

    8x1
    4x1, 2x2

    Benchmarks show that 8 slot configurations move data faster.

    That's why I went with 14 (2x1, 6x2). An odd number, but I used my stock ram and saved a little dough over going for 16 gigs.

    No one has an opinion on single gig sticks in slots 1&2 vs slots 7&8?
     
  8. nicolasmasset macrumors regular

    Joined:
    May 25, 2007
    Location:
    Belgium
    #8
    Yeah sorry, I meant 4x2 :)

    But here's another question! Earlier today I rang the apple reseller to ask what I should keep in mind when buying ram. He said that a higher mhz ram is allowed, it will scale down to 800mhz for the octo 2.8 no prob.

    Is that true? Cause at owc, the 4x2gb 1066mhz option is about 40$ cheaper than the 4x2gb 800mhz option!! From 180$ to 140$!
    And even more if you choose 16gb!
     
  9. grue macrumors 65816

    Joined:
    Nov 14, 2003
    Location:
    Somewhere.
    #9
    PC8500 isn't pin compatible, and wouldn't have the necessary heat sinks.
     
  10. nicolasmasset macrumors regular

    Joined:
    May 25, 2007
    Location:
    Belgium
    #10
    I'm sorry, I don't understand. Don't all FB DIMMs have heatsinks? But you're probably saying that the new ones are DDR3 and that their footprint is different so they won't fit into the slots?
     
  11. grue macrumors 65816

    Joined:
    Nov 14, 2003
    Location:
    Somewhere.
    #11

    THe 2009 models don't use FB-DIMMs.
     
  12. sparkie7 macrumors 68000

    sparkie7

    Joined:
    Oct 17, 2008
    #12
    my understanding (with the MP 2008) is that its better to not have all 8 slots filled. The optimum was 4 slots (for eg. 4x4GB = 16GB), Loading all 8 slots was ok, but was not the optimum config
     
  13. sparkie7 macrumors 68000

    sparkie7

    Joined:
    Oct 17, 2008
  14. Tesselator macrumors 601

    Tesselator

    Joined:
    Jan 9, 2008
    Location:
    Japan
    #14
    Yes it is. I had it all ways and I noticed the difference in many areas of operation with 4 or 8 in place. My benchmarks also went up a bit!

    But 4 and 8 are the same AFAIK. it's 2 and 6 modules that are slower. Also to be aware of is that 1GB, 2GB, and 4GM modules draw about the same amount of power each so 4x2GB is going to be cheaper and cooler than 1x8GB etc.

    Also as i understand it if you have 2x1GB and 2x2GB then only the the 1st four GBs of system RAM will be accessed in quad-channel and the second gig of each of the two 2GB DIMMs will be accessed at the slower speed. I've not tested this but I read it somewhere credible (I think) like Tom's Hardware or something.


    The linked article seems to confirm my 8 vs. 4 beliefs as well:

    Memory performance—8 modules vs 4

    AnandTech has an interesting article “Understanding FB DIMMS”, as part of its discussion of the new Apple Mac Pro (FB-DIMMS are the technical name for the type of memory module used by the Mac Pro).

    The claim is that filling all 8 memory slots will in theory reduce memory performance over using just 4 slots due to the nature of the serial data transfer in an FB-DIMM—increased latency of 3-5 nanoseconds.

    Using diglloydTools, I measured no difference in memory copy speed with memory in slots A3/B3 and A4/B4 as compared with slotsA1/B1 and A2/B2. That doesn’t mean there isn’t a difference in some real world applications, because bandwidth and latency are independent factors.

    Furthermore, Photoshop test results show clearly that such theoretical concerns are a waste of time; performance for any challenging task depends on the total amount of memory.​

    .
     
  15. nicolasmasset macrumors regular

    Joined:
    May 25, 2007
    Location:
    Belgium
    #15
    So 4 is better than 8 slots for heat, power consumption and latency issues?
    Here are my options, on my current macbook I usually fill up 2.5gb when doing moderate audio projects!

    1) stock 2x1 plus 6x1 (8gb total, 8 slots filled) = 180 euros
    2) stock 2x1 plus 2x2 (6gb total, 4 slots filled) = 100 euros
    3) stock 2x1 plus 4x2 (10gb total, 6 slots filled) = 200 euros
    4) stock 2x1 plus 2x4 (10gb total, 4 slots filled) = 140 euros

    I'm leaning towards option 2 or 4. With those options, if I ever need more, I wouldn't have to throw away the 1gb modules. And between those to I think I'd go for option 4 considering the small price jump for 4gb extra.

    What do you guys think?
     
  16. Tesselator macrumors 601

    Tesselator

    Joined:
    Jan 9, 2008
    Location:
    Japan
    #16
    I don't know about latency issues but yes to the other two.

    I agree. #4 looks like the sweet spot. :)

    But wait... "Macbook"??? OIC, NM... :p
     

Share This Page