Memory Bandwidth Benchmark Score Questions?

Discussion in 'Die-hard Overclocking & Case Modifications' started by Roger_D25, Jan 2, 2006.

  1. Roger_D25

    Roger_D25 Ancient Guru

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    Hey Guys,
    I have some interesting results I need some help understanding! Since I got my new Opty 148 (CACJE 0546) I have been methodically testing, tweaking, testing, tweaking, etc.... In the process of this testing I had been periodically using SiSoftwares SANDRA RAM bandwidth benchmark test. When my RAM is at stock levels (DDR 400, 2.6v, Timings 2-2-2-5) I get somewhere in the region of:

    Int Buff'd iSSE2 7173MB/s
    Float Buff'd iSSE2 7098MB/s

    Well as you would expect as I increased the FSB/HT this bandwidth also increased until I reached about (270/DDR540, 2.75v, Timings 3-4-4-8) with a score of:

    Int Buff'd iSSE2 7052MB/s
    Float Buff'd iSSE2 6958MB/s

    I am able to increase the FSB/HT higher but I havn't testing for stability at that level so it is not important. 270/DDR540 is the highest I have gone with tested stability (Memtest-86 v3.2 9hours with no errors). Well two days I decided to lower clock speed to about 2.8 (Stock voltage 1.4v) because I am now back at work and didnt' have time to continue stability testing. With the CPU at 2.8Ghz I have my RAM speed at (255/DDR510, 2.65v, 2.5-3-3-7). I then ran SANDRA's memory bandwidth benchmark test to see what my score would be like at that lower level. I was expecting to get somewhere around 6k for both Int/Float but was very suprised to see that I get the highest bandwidth I have ever had before at:

    Int Buff'd iSSE2 7173MB/s
    Float Buff'd iSSE2 7098MB/s

    So the question is, why with my RAM speed much lower am I getting higher memory bandwidth than when my RAM is maxed out? Also my memory bandwidth efficiency is higher as well at 88%. It was only 72% when memory was set at (270/DDR540, 2.75v, Timings 3-4-4-8). The only real difference between the two runs besides memory speed is my timings. With my RAM set as a speed of DDR510 I am able to run tighter timings than with memory speed at DDR540. With that said, can this small difference in memory timings make such a large difference in my memory bandwidth? Any help would be greatly appreciated! Thanks guys
     
  2. BuildeR2

    BuildeR2 Ancient Guru

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    Well, I don't have an AMD 64 or Opty system but I think the reasons are these. Your efficiency changes because when your RAM is at stock and doing 7GB/s it is fulfilling 88% of it's bandwidth. When the RAM is at a divided ratio (such as 5/4) it has more potential bandwidth but since it is still only producing 7GB/s of speed , it is using less of the potential bandwidth available. Hence the reason it says 72% or so. I am pretty sure that AMD 64's and Opty's are highly dependant upon RAM timings rather than higher clocks. Try keeping your timing at 2-2-2-5 or 2-3-3-6 and see how high you can get it stable. I hope this helps some.
     
  3. Roger_D25

    Roger_D25 Ancient Guru

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    Thank you very much for replying so quickly. I have heard that unlike Intel CPU's the AMD64 processor's do react better to timings more than straight clock speed/ram speed. Also I am fairly sure like you said that the trick is to get a good balance between RAM speed and tight timings.
     
  4. texanterror

    texanterror Master Guru

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    i only get about 69xx or so with 200 2-2-2-5 and i jump to about 72xx i think with 266 3-4-4-8 1T but 2T i drop back to about 7xxx.. also i found that about 240 2.5-3-3-7 1T is about the same for the 266 3-4-4-8 timmings at 1T also.. i can only give my ram 2.8v cuz of my mobo so if i play for a while i guess i have a unstable part of ram at 266 3-4-4-8 1T probaly just .05v would help but i get a crash after 3 hours or so playing bf2 or something that pushes my systems limits.. so i just keep it at 2T for my gaming and everything maybe a slight bit in benches super pi whatever but bf2 wouldnt notice anything.. im always first to load into a server after a new map out of everyone.. hehe
     

  5. targett

    targett Master Guru

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    7100 stock hmmmm

    PC3200 dual channel has a max of 6400mb/s thats @ 100% efficency.

    most likely your stock score is around 6000mb/s and that would make the rest of your score right.

    targ
     
  6. Roger_D25

    Roger_D25 Ancient Guru

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    I must agree with you on this, 7K at stock levels is a tough sell. Even at higher levels like 230-250 that is pretty decent bandwidth. There is a chance something is setup wrong or SANDRA is having a bug with your system texanterror. Then again I could be completly wrong and that is exactly what your getting so sorry if my skeptisism is uncalled for!

    I'm trying to find my imageshack registration link so I can post my screenshot of my latest run. I'll hopefully post back soon with the screenie. Thanks for the post's guys


    Alright I finally found my image shack link. Here is my screenie that shows the pertient info:
    [​IMG]
     
    Last edited: Jan 2, 2006

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