AM3 and memory speeds

mikeymikec

Lifer
May 19, 2011
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After reading this thread: http://forums.anandtech.com/showthread.php?t=2236463

I did a bit of googling.
I found this article:
http://www.legionhardware.com/articles_pages/amd_am3_memory_performance_guide,1.html

Which IMO says that there's not a great deal of difference either looking for tighter timings or higher frequency RAM, however I also found this:

http://forum.giga-byte.co.uk/index.php?topic=2515.0;wap2

Admittedly it's a forum post, so I wouldn't treat it as gospel, but this bit caught my attention:

Having actually talked to an AMD Technical Guru to establish their views on this subject, I can now state, with confidence that:

You are better off not trying to run your RAM above 1333 Mhz. when using an AM3 Phenom or Athlon CPU.
If you do so, you run the risk of system instability and even damaging the Memory Controller on the CPU.

Considering that just about every AM3 board I've seen allows you to easily change the speed that the memory runs at in the BIOS without being regarded as an overclocking option, I find this a bit hard to believe.

- edit - checking the manual for my board, I do however notice that the option for increasing the DRAM speed is under "Ai tweaker", so they might regard it as a "do at your own risk" sort of option rather than the possible "use this setting if the board doesn't auto-detect the most ideal speed your RAM says it can do".

Thoughts? Has anyone encountered any other articles that examine the effect of RAM speeds and timings on AM3 setups that you would recommend I read?
 

KingFatty

Diamond Member
Dec 29, 2010
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I remember looking into some reviews that analyzed the effect on performance between running at 1333 vs 1600 etc. (it's very hard to notice a difference), but I haven't seen anything analyzing how the AM3 CPU is affected one way or the other.

I have 1600 ram, but I run it at 1333 speed because that lets me use a lower DRAM voltage and I think I can get a higher overclock on the Phenom II cpu and cpu-nb, I think?

What would be the mechanism that would cause harm to the CPU/memory controller? I mean, it's a difference in speed we are talking about here, so I don't see how damage would occur because there is no increase of voltage or heat, so what would cause damage? I'd think the chip would just say "oh that's too fast, I'm confused /CRASH" without getting damaged.
 

mikeymikec

Lifer
May 19, 2011
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I tried a very quick bit of testing on my setup (960T with all cores unlocked, 4GB dual channel DDR3-1600 RAM), and found a slight reduction in performance when testing with 7-zip and WinRAR's benchmark tools.

How much are you able to under-volt your RAM by? In CPU-Z the profiles for my RAM all say 1.5v.
 

KingFatty

Diamond Member
Dec 29, 2010
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I was sloppy with my phrasing, to clarify, I have a set of corsair and a set of OCZ - and their profiles specify a lower voltage at 1333 but a higher voltage at 1600. So when I set the DRAM voltage to auto, the profile @ 1600 says to use 1.65V, but when I use the default 1333 setting, the auto voltage puts it lower, I think 1.5V?