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CPU:DRAM on AMD790FX

Discussion in 'Overclocking & Cooling' started by robal, Aug 12, 2008.

  1. robal

    robal

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    Hi,

    CPU:DRAM on Amd platform.
    Can somebody clarify this for me ?

    All my AM2 systems (Asus M2R32-MVP; Gigabyte GA-MA79FX-DS5) don't have this setting in bios.

    All I can do is play with FSB or CPU multiplier. The memory clock gets set by bios somewhere near stock speed. No matter how I overclock my CPU (by FSB or by divider [X2 black edition]), memory stays near stock.

    I see in CPU-Z that CPU:DRAM divider increases as I overclock, so the RAM speed stays stock.

    Is there a way to get performance out of 1066Mhz DDR2 without using Phenom ?
     
  2. robal

    robal

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    Bump...

    uh... Any overclocking expert there ?
     
  3. miloshs

    miloshs New Member

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    My experience is that on an 790FX board you can manipulate the speed of your RAM only by selecting it's speed in BIOS... if you set your RAM at 667mhz in BIOS you will be able to overclock your FSB and CPU without overclocking your RAM over the 800mhz margin...
    Altho if you have 1066mhz RAM u can overclock FSB/CPU without lowering the speed in BIOS... Since your 1066mhz RAM is running by default @800mhz (if you don't have Phenom CPU), you can easely overclock the FSB with no concerns until RAM speed increases to 1066mhz!

    The only way u can benefit from running 1066mhz RAM on a 790FX board coupled with an X2 CPU is to overclock your FSB, or tighten the timings on your DDR2...

    Your RAM is probably 1066mhz CL5 rated at 5-5-5-15, so you can either:

    1. overclock your FSB so your RAM reaches 1066mhz @ default timings 5-5-5-15 (this is probably better on Intel CPU's),

    2. leave your FSB alone, hence not overclock the CPU (unless you have 5000+BE, 5400+BE, which can be overclocked by increasing the multiplier) and tighten the timings at 4-4-4-12 and adversly increase speed of your RAM so it runs close to its rated speed (1066mhz@CL5 is almost equal as 800mhz@CL4),

    3. lower the ram speed to 667mhz in BIOS, overclock your FSB and CPU so your RAM gets back to around 800mhz or a bit more and tighten the timings to CL4 (4-4-4-12), and get increase in speed in all of your components (FSB,CPU,PCIe,RAM...)

    these are only a few options...

    Also bear in mind that default HTT speed for an 790FX board is 1000mhz... for a successfull high FSB overclock it is best to lower HTT speed to 800mhz, as it will also increase proportionally with FSB increase (1:5 ratio whn HTT is at 1000mhz in BIOS or 1:4 ratio when its set at 800mhz in BIOS)

    So increase in FSB from default 200mhz to 220mhz would increase your HTT to 1100mhz (1:5) or 880mhz (1:4)...

    Hope i didn't get it too complicated for you here... :toast:

    EDIT: Also if you want to oveclock anything it is best to turn off AMD Cool & Quiet setting in bios, as if left ON it will decrease your CPU speed once the usage of your CPU is low...
    If you just need more performance from your RAM option 2. is the best choice, then again if you want all-round speed (overclock) increase option 3. is the way to go :)... and all of that just with your RAM around default speed... You can always experiment more, to get more increase...
     
    Last edited: Aug 24, 2008
    robal says thanks.
  4. miloshs

    miloshs New Member

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  5. robal

    robal

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    Thanks for a good explanation Miloshs !

    Actually, I'm doing it this way at the moment (increasing FSB to OC memory and keeping HTT at reasonable level).

    The problem is with CPU:DRAM divider.
    The article you pointed me to gives a great explanation to this thing.

    Basically CPU:DRAM divider is something around CPU multiplier / 2.
    That limits, what you can do with memory clock.

    I'll try fiddling with latencies then.

    Again, thanks !
     
    Last edited: Aug 25, 2008
  6. miloshs

    miloshs New Member

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    No problem mate...
    Just bear in mind that AMD CPU/MOBO combo,speed vise, benefits more by getting RAM latencies faster than increasing RAM's speed...
    Eg. better off having 800mhz with tight,tight,tight latencies than 1066mhz with crap latency :toast:

    Cheers, have fun overclocking your stuff :cool:
     
  7. nanohead New Member

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    Milosh gave a nice reply and is consistent with what I have learned with my 790FX boards over the past 8 months or so.

    Only 1 thing I would add is that one of the only things AOD is useful for, is dynamically setting memory timings. It works most of the time (not always, does cause some crashes here and there)

    I got my X3 machine running its fastest by using AOD and setting the memory timings, and then using Everest Memory Benchmark tool to see what impact it had. The process actually worked to my surprise!!
     
  8. miloshs

    miloshs New Member

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    Never trusted the AOD myself, but will have to try it out and see how it goes.... it's a nice feature not having to have to go BIOSing, loading XP, BIOS, XP, BIOS, XP .... :rockout:

    I trust you set it manually in BIOS after you found the timing limits in win using AOD?
     
  9. nanohead New Member

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    Yes, had to manually enter into BIOS.

    AOD does suck for most things, although maybe we've found a new use for it :toast:
     
    miloshs says thanks.
  10. miloshs

    miloshs New Member

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    Now with a chance for going off topic, but how does the Phenom X3 perform? I see you have it in your rig? Any problems or anything alike? Better than X2 and weaker than X4???
     

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