RAM compatibility with CPU and mobo

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Anguser

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Hi,
A few months ago I did read that it is the mobo which decides the RAM compatibility. But on CPUboss I noticed a point named 'compatible RAM frequency'. Before that I thought if a RAM is compatible with mobo then it should be compatible with all the CPUs with the same socket type. But it seems its not that simple.
So, for e.g. If a RAM say 1600mhz is compatible with a mobo(say am3+) but CPU doesn't support it (Fx 6300 which supports only 1866mhz as per CPUboss) then will it be a total mess?
I searched the web but found mixed things, some say mobo matters and cpu not at all and some say different.
So please help me learn these things.
And, before using #-#-#-#, please explain what these numbers mean.
 
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Hlsgsz

Hlsgsz

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First of all, never ever take CPUBoss into accout. That site is b****it.
Second, it used to be the motherboard that supported this or that on the ram side, but nowadays the controller is on the CPU, so it depends on both the CPU and MB chipset(you must look at the cpu specs and the mb specs, and the max you can use without overclocking is the slowest of the two.)
Third, when a CPU(or MB) supports that max frequency you find in their specs, it also supports anything below(so an FX6300 can work with 1866, 1600, 1333 aswel as 1060).
 
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Anguser

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Ok, so if a mobo supports Xmhz and a cpu supports Ymhz where X<Y, then cpu will be downclocked to Xmhz even if X is not mentioned in its specs, is that right? So, it's just like what happens when two different frequency rams are used together right?
 
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Anguser

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Thank You for your quick response.
And also is their anything else related to build's compatibility that I should consider?
Are those #-#-#-# numbers very important? If so then I will be happy to learn that.
 
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Hlsgsz

Hlsgsz

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Yes and no. Whn using two different rams they will both work at teh frequency of the slowest, so one could say that the faster one is downclocked. In teh case of the cpu this is not the case. It's all about a multiplier from the base frequncy. the cpu itself works at its normal frequency.
Basically, it makes no difference in real world applications if you are using a discrete GPU. If using integrated graphics, then you should get the highest frequency possible as that will help.
 
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Hlsgsz

Hlsgsz

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Those are memory timings as follows:


  • ■ CL: CAS Latency. The time it takes between a command having been sent to the memory and when it begins to reply to it. It is the time it takes between the processor asking for some data from the memory and then returning it.
    ■ tRCD: RAS to CAS Delay. The time it takes between the activation of the line (RAS) and the column (CAS) where the data are stored in the matrix.
    ■ tRP: RAS Precharge. The time it takes between disabling the access to a line of data and the beginning of the access to another line of data.
    ■ tRAS: Active to Precharge Delay. How long the memory has to wait until the next access to the memory can be initiated.

The lower they are the better. And when pairing different rams, the will work at the highest of the two.
These are less important than frequency, but out of them, the one that matters is CL. Like i said, the lower the better. And, again, they make little to no difference in real world applications when using a discrete GPU.

Further reading:
http://www.hardwaresecrets.com/understanding-ram-timings/
 
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Anguser

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You have covered good points regarding my first question, thank you.
But still to be more clear,
By this, 'In teh case of the cpu this is not the case. It's all about a multiplier from the base frequncy. the cpu itself works at its normal frequency.' what do you mean can you explain in more detail.
Do you mean, I can get a high frequency cpu, and it will work with all low frequency MBs?
And the converse of this question will be not true right?
 
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Hlsgsz

Hlsgsz

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It means that there is no link. The CPU will work at its normal frequency regardless of the ram and mobo. And it doesn't matter witch has the higher specs MB or CPU.
 
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Anguser

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Regarding the timings's question Hlsgsz your answer explains basic terms in short.
And Tradesman 1 the FAQ page you linked contains much questions which I have but I will take some days to read all that.
Thank You
 
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Anguser

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I'm sorry, but again, by normal frequency what do you mean?, what memory controllers normal frequency?, the base frequency you mentioned before, which is multiplied by some factor?
Do you mean any cpu can work with any MB?
If, so then it again comes to this that, cpu doesn't matter in this, it will work with any RAM frequency.
(Sorry for asking again and again but I want a clear picture about it.)
 
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Tradesman1

Tradesman1

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Your CPU is suppose to be able to run up to 1866 DRAM at 1 stick per channel, many can run faster DRAM and more sticks. (Depends on the individual 6300). While the mobo can often support faster DRAM, the defining factor is how strong the MC (memory controller) in the CPU is. With a 6300 I'd stick with with 1600 or 1866 sticks
 
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Anguser

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I don't have the fx 6300 it was just an example. So, in general you are saying higher MC frequency cpu can work with lower frequency RAM?
e.g. I3 4150 supports 1600 means it supports all lower but not 1866, and fx 6300 supports 1866 so it supports all lower freq.s right? And does the same applies to mobo?
And what do you mean by 'individual fx6300'?
 
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Tradesman1

Tradesman1

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It all depends on the individual CPU you get, some 6300, as an example, can run 2133 DRAM, others 1866, some labor to run over 1600. It all depends on the individual CPU and the MC in it. Much the same as some 6700Ks can run 4.9 or 5 while others can only get to 4.5 or 4.6 (silicon lottery). Good example here about how much different CPUs of the same exact model can differ:

http://www.hardocp.com/article/2013/06/01/intel_haswell_i74770k_ipc_overclocking_review/6#.VyraYFUrJD_

Mobos are more limited by the chipset, i.e. Z170s can run most any DRAM 9that the CPU can carry), where h170 chipset mobos show as a max of 2133
 
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Anguser

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Ha ha, so in this way comparisons between even same models can give different results!! It's surprising and funny to hear.

And regarding mobos, you used 'max' 2133 in last line, so is it right that all the frequencies below the frequency mentioned in specs will work?(for both cpu,MB)
 
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Anguser

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It's a bit specific motherboard model oriented.
So let's take H97 as e.g., so if on box it's mentioned it supports 1600 then it will support all lower frequency say 1333?
In short when I go in store how do I know the RAM is compatible with mobo and CPU?
The CPU part is clear enough but now I'm confused about mobo compatibility.
 
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Anguser

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Refer to my 1st response (with X,Y), is the opposite of that true? If mobo supports Ymhz will it downclock to any frequency (Xmhz), where X<Y or it will be supported to only specific Y frequencies mentioned on box?
 
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