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A64 Systems Ram Guide


shogan191
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The following information is provided by Revivalist and makes it easy to understand setting your ram speed using a divider. Thanks Reviv.

 

 

About the "problem" with RAM speed being lower then you would expect with a given divider. . It's not a problem with some motherboards. It's is because there's a little detail about A64 systems that a lot of people neglect, or they are simply unaware of. It's simply this:

 

"The RAM speed must be a whole number multiplier of the CPU speed. If it's not, then the RAM will slow down until it is." . . . In other words, if you divide the CPU speed by the RAM speed, you have to get a whole number. . .

 

Let me give you an example from my own system. . . . I'm using 325HTT with a 10x multi for 3.25GHz CPU speed. Let's say I use a 9/10 divider for my RAM. Then I would expect my RAM to run at

 

325MHz x 9/10 = 295.5MHz, right? . . . . Wrong!

 

The reason is because I also have to take into account the principle I mentioned above: "The RAM speed must be a whole number multiplier of the CPU speed. If it's not, then the RAM will slow down until it is."

 

So we need to check if 295.5MHz is a whole number multiplier of 3250MHz (my CPU speed). So let's check . . .

 

3250MHz / 295MHz = 11.1111. . . .

 

Clearly this is not a whole number. This means that the RAM speed will slow down until it is a whole number. In fact, the RAM would have to slow all the way down to 270.8MHz so that we have

 

3250MHz / 270.8MHz = 12

 

That's the reason why the RAM ends up slower than you might think. The reason for all of this is because the memory controller is on the CPU die and must be "synchronized." I don't know the technical details beyond this, but this is why it's something that's unique only to A64 systems.

 

By the way, none of this confusion arises if you run 1:1 and also never use 0.5 CPU multis. Then you're always gauranteed to have the RAM speed be a whole number multiplier of the CPU speed. . . .

 

There's actually a handy little program that will quickly calculate your RAM speed for different HTT speeds and CPU multis. that you give it. I'll try to find the link and post it. :) . . .

 

Edit: Alright, I found it. . . Go to this link and download the file attached to the first post. It's a wonderful little calculator that does all the work I described above automatically. :)

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