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Old 02-07-2006, 08:33 AM   #1 (permalink)
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Question FSB and DDR clock relationship

I have to know somethin before overclocking. How the clock of dual channel memory effected by FSB?

For example if certain AMD runs on 200 FSB, so the 400 MHz memory chip runs on 400 MHz?
If so, then how it goes with Intel? 800 FSB while using 400 Mhz memory chip?
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Old 02-07-2006, 09:52 AM   #2 (permalink)
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DDR does not actually run at DDR speeds. e.g DDR 400 is not 400 mhz. it runs at 200mhz. DDR= Double Data Rate. the way i understand it works is that it reads/writes at the peak and fall of each clock cycle, effectively doubling the data that can be transferred in that time. so when adjusting the "FSB" of an AMD cpu from say 200, keep in mind that unless you are running a memory divider the memory speed will be double the FSB.

edit: i figure that you confused dual channel and DDR because dual channel is different and doesn't effect overclocking
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Old 02-07-2006, 01:11 PM   #3 (permalink)
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Default memory devider :o?

And how do you run such 'Memory Devider'?
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Old 02-07-2006, 03:26 PM   #4 (permalink)
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Well, I really thought that DDR was "dual data something", in other words dual channel. But what you nitestick said really makes it more logical.

But I still didn't get it, talking AMD, if I run FSB clock on 200 while using so called "400 Mhz" memory chip, I actually using the full speed the memory designed for?
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Old 02-07-2006, 04:07 PM   #5 (permalink)
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Yes, you are. Since it is 'Doulbe Data Rate' Ram, they are actually putting you on. It does not run at 400mhz, ever. It runs at 200mhz, but does the work as if it were running at 400mhz.

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Old 02-07-2006, 04:27 PM   #6 (permalink)
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And one more question.
Talking about the Intel CPUs running on 800 FSB, it just using memory divider (like FSB/4), so the actual memory clock is 200Mhz as well?
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Old 02-07-2006, 05:28 PM   #7 (permalink)
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the actually fsb of the p4 would be 200mhz, but it's quad pumped sending four signals with each clock, making it 800mhz
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Old 02-07-2006, 08:07 PM   #8 (permalink)
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^^ that sums it up. don't worry about the dual channel/DDR thing its a common misconception. dual channel is when you have your memory across 2 seperate memory channels on the motherboard effectively doubling the bandwidth. as opposed to running both sticks on the same channel.
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Old 02-08-2006, 12:52 PM   #9 (permalink)
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So, what you say is that the memory in the 200 FSB AMD and "800 FSB" Pentium is actually running on the same speed?
And the same memory used in AMD could be used in Pentium, even if the FSB is different?
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Old 02-09-2006, 08:25 AM   #10 (permalink)
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yeah basically. although there is a difference when you are talking DDR and DDR2
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