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1866MHz RAM to be used with lower timings (1333MHz bus CPU) - Page 2

post #11 of 18
Quote:
Originally Posted by Flamingo View Post

Officially they will never try to go beyond what AMD has specified.
if 4 slot configs work with 1600mhz then "officially" they wont support it under the phenom II cpus. only for the bulldozers/visheras and only under single channel or mixed single and dual channel.
Well if you look at the stock speed of the NB. It is 2000 and this is the base that AMD went with. NB 2000 = Ram speed 1333.
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post #12 of 18
Quote:
Originally Posted by alexan_e View Post

The list I refer to is http://www.asus.com/ROG/CROSSHAIR_IV_FORMULA/#support_QVL
I can see several 1600MHz models supported for 4 dimm configuration and several 1600MHz which are not
This is also true for 1333MHz, 1066MHz etc so I'm not sure what the problem is with those that "can't work", it doesn't seen to be the frequency.

Alex

When motherboards mention the RAM speeds supported, they are not including all the CPUs in their test run. Even though 1600mhz is supported officially on the motherboards, it will only be on select processors (the FX series in this case) whose memory controllers can take handle that frequency.

ie: officially Thubans dont support mem freq above 1333, but because they are good cpus for overclocking they can handle 1600mhz ram speeds easily

this explains it better: http://hardforum.com/showpost.php?p=1037427142&postcount=28
Quote:
All AMD motherboards are capable of setting memory at 1600Mhz (x8 multiplier, often undocumented), just the AMD CPU IMCs themselves are only rated for 1333Mhz. The reason for this is IMC limitation; according to this official AMD document, you would require an NB speed of 2400Mhz (above default 2000Mhz spec and requiring more than 1.15V) to not bottleneck 1600Mhz. NB speed must be 3 times the speed of the RAM (before DDR). 667 [1333 DDR] x 3 = 2000. 800 [1600 DDR] x 3 = 2400. However, if you overclock the NB to 2400Mhz and run 1600Mhz memory, you will see the performance benefit; otherwise you won't, so AMD did not bother rating the IMC at above DDR3-1333. If the IMC/NB were capable of being within spec to run 1600Mhz, then 1600Mhz would run with no problem across all of the AMD IMC revisions (C2, C3 and E0) and provide adequate performance benefit. And in most cases, the NB can be overclocked/overvolted to meet that minimum 2400Mhz spec.

So if you want to go by the official supported speeds you have to consider what speeds your CPU can handle and not only the motherboard.
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post #13 of 18
Thread Starter 
Quote:
Originally Posted by Flamingo View Post

So if you want to go by the official supported speeds you have to consider what speeds your CPU can handle and not only the motherboard.

But I don't intent to use the 1866MHz RAM at that frequency with the current cpu, it is going to be used will lower frequency (say between 1333 which is the nominal speed up to 1600), are you saying that this is a problem ?

Alex
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post #14 of 18
Quote:
Originally Posted by alexan_e View Post

But I don't intent to use the 1866MHz RAM at that frequency with the current cpu, it is going to be used will lower frequency (say between 1333 which is the nominal speed up to 1600), are you saying that this is a problem ?

Alex

Most likely scenario: On the first run with no other dimms installed, there will probably a hiccup in the first run, later the system will restart and automatically adjust the RAM to 1333mhz. Or it might just go 1333 speed on the first boot itself.

I was just saying that if you wanted to run the 1333++ speed memory on a Phenom II X6, it wont provide any performance benefit unless you increased the CPU-NB freq too.

So go ahead with either the 1600 Gskill or the 1833.
Edited by Flamingo - 2/11/13 at 7:55pm
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post #15 of 18
Thread Starter 
Quote:
Originally Posted by Flamingo View Post

Most likely scenario: On the first run with no other dimms installed, there will probably a hiccup in the first run, later the system will restart and automatically adjust the RAM to 1333mhz. Or it might just go 1333 speed on the first boot itself.

I was actually wondering about that, if the system will try to use 1866MHz while set to auto (until I have a change to change it manually), then you for clearing that.

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post #16 of 18
DDR3 systems can not automatically default to anything higher than DDR3-1600 CL11. Depending on BIOS and RAM, it will default to DDR3-1333 CL9 or DDR3-1600 CL11. From there, you can manually input settings for DDR3-1600 or DDR3-1866, or DDR3-1333 with low timings. By purchasing a high memory spec like DDR3-1866, you can downclock to DDR3-1333 and run timings like 7-8-7-24 1.50V. This would be much better than keeping everything AUTO default at 9-9-9-24. So whether your CPU can't support it, or you don't want to overclock the CPU, using a high frequency RAM can still be beneficial.

Cheers
post #17 of 18

Don't bother with the QVL. In today's world of memory controllers integrated with the CPU, laziness in updating QVLs, and several kit brands coming out, QVLs are useless as a strict measurement for compatibility.

 

Everyone else has said what needs to be said thumb.gif

post #18 of 18
Thread Starter 
I saw in this guide AM3 CPU's Which Ram Speed is Faster and Which CPU-NB Clock is Best and it says that lower timings are better.

The RAM I ordered is 2x4GB set F3-14900CL9D-8GBSR (G.Skill sniper 1866MHz DDR3),
the timings for 1866MHz are 9-10-9-28-2N, any idea what are the timings for this memory used @1333MHz and @1600MHz?

I haven't received the RAM yet but an SPD I found shows worse timings for lower frequencies, how is this possible?



Alex
Edited by alexan_e - 2/15/13 at 10:05am
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