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Dual Channel Memory


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30-Nov-2005, 12:41 AM #1
Dual Channel Memory
Dual Channel Memory - Using DDR400(PC3200) Memory Modules

Channel A
DIMM 0
DIMM 1

Channel B
DIMM 0
DIMM 1

CHANNEL A DIMM 0 + CHANNEL B DIMM 0 = 6.4 GB/s transfer rate
(3.2 GB/s) (3.2 GB/s)

CHANNEL A DIMM 1 + CHANNEL B DIMM 1 = 6.4 GB/s transfer rate
(3.2 GB/s) (3.2 GB/s)

6.4 GB/s + 6.4 GB/s = 12.8 GB/s accumulated transfer rate

Does this sound right? I am confused about the concept of Dual Channel. I read many detailed articles on Dual Channel DDR based memory, but am slighty side-tracked. One DDR400 memory module on channel A in position 0, and one DDR400 memory module on channel B in position 0 take their individual transfer rates of 3.2 GB/s and added together = 6.4 GB/s, correct? Vice versa for Channel A and B position 1. Maybe someone can lend me a URL with a more detailed description? This is one of the articles I have reviewed.


http://www.kingston.com/newtech/MKF_...whitepaper.pdf

Thanks for the advice in advance.
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30-Nov-2005, 12:57 AM #2
This link may explain things easier for you.
http://www.hardwaresecrets.com/article/133/2
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30-Nov-2005, 07:37 AM #3
It might if it wasn't a dead link. ;[
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30-Nov-2005, 07:53 AM #4
it was just accessed here. try pasting it on your browser. that should get you there.
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30-Nov-2005, 09:20 AM #5
Dual channel memory simply means the CPU reads and writes to two sticks at time through two pipelines between the CPU and the memory, compared to a single pipeline on single channel systems. There is nothing special about the memory itself except that they come in matching sticks for compatibility with each other.
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30-Nov-2005, 04:41 PM #6
Thanks for the response Rukee, but I am fully aware of that. What I am trying to understand, in a simplified explanation, is whether you need 2 memory modules to acquire the accumulated transfer rate. For example. If you have 2 sticks of DDR400(PC3200) memory, one on channel A and one on channel B, will they total at 6.4GB/s because they both run individual transfer rates of 3.2GB/s? Or do they run at the normal 3.2GB/s, and you need the remaining two empty DIMM slots housing DDR400(PC3200) memory modules for it to total at 6.4GB/s? If I am right, having four DDR400(PC3200) memory modules running dual channel, your total transfer rate would max out at 12.8GB/s.

Mathematical Example
(3.2GB/s + 3.2GB/s = First channel A&B pair total transfer rate)
(3.2GB/s + 3.2GB/s = Second channel A&B pair total transfer rate)
(6.4GB/s + 6.4GB/s = total accumulation of 12.8GB/s transfer rate --with all four DIMM slots housing DDR400(PC3200) memory modules--)

I know not many people will be able to answer this, but to who answers this question, great appreciation!
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30-Nov-2005, 04:46 PM #7
you still get past the 6.4gb due to only two channels. the increase of memory means
an increase in capacity for active ram.
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30-Nov-2005, 04:49 PM #8
yes, theoretically two sticks, 1 each in the correct slots will do over 6.4GB/s in dual channel whereas 3.2 is about it for single channel.
This can be verified with the Sandra bandwidth benchmark.
4 full slots will force the 2T command rate and drop the memory speed from 400 to 333(I think) this is a limitation of the CPU`s memory controller, not the motherboard or memory sticks. That`s why it`s always best to run 2 sticks instead of 4.
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30-Nov-2005, 04:51 PM #9
So you only need two memory modules for the data rate to double? 2 DDR400(PC3200) memory modules would run at 6.4GB/s? So 4 DDR400(PC3200) memory modules would run a grand total of 12.8GB/s, right? (6.4 + 6.4). And likewise for all other types of RAM. e.g.)
2 DDR333(2700) would run at 5.4GB/s, and 4 DDR333(PC2700) memory modules would accumulate a total of 10.8GB/s?
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30-Nov-2005, 05:03 PM #10
Yes you need just two sticks for dual channel and no, 6.4 is the limit of the CPUs memory controller without overclocking. Here is a screenshot of some of the Sandra benchs, the memory bandwidth is circled. This is with the system in my sig.
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30-Nov-2005, 05:12 PM #11
Almost, except 400Mhz has a bandwidth of only 3.2GB/s - hence the spec name of PC3200. PC2700 has a max bandwidth of 2.7GB/s.
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30-Nov-2005, 05:17 PM #12
So even with 4 DDR400(PC3200), you'll still max out at 6.4GB/s instead of 12.8GB/s? So I'd guess the two memory modules being housed in DIMM 0 of CHANNEL A and CHANNEL B determines the total sum of memory transfer rate, and the rest is just added memory storage? Correct?
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30-Nov-2005, 05:28 PM #13
capacity takes the load of the cpu. the more capacity results in faster cpu rates due
to having less demand placed on cpu time. data is proceesed smoother with less of a
bottleneck at the cpu end. you see this with cad as well as other large programs.
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30-Nov-2005, 05:41 PM #14
that`s not true, more RAM adds to CPU demands and it can be proved with a couple diffrent sized kits, it`s harder to overclock with a 2gig kit then with a 1 gig kit. The guys at the OCZ forums can verify that.
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30-Nov-2005, 05:46 PM #15
Thanks for all of the valuable input, but one of my questions has not been answered or I am just not understanding the format of your answer. If you have a 4 DIMM Dual Channel memory system, will the max transfer rate be calculated by 2 memory modules -in this case DDR400(PC3200)- (3.2GB/s and 3.2GB/s = 6.4GB/s) and any other memory modules you install will only add more capacity and not affect the transfer rate? Correct? Because from what I understand, the memory controller will recognize the transfer rate of 6.4GB/s and not 12.8GB/s because it only calculates the total transfer rate though the memory modules inhabiting DIMM 0 of CHANNEL A AND CHANNEL B.
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