Clearing up some confusion about dual channel

[Neil27]

I have asked this question before, but have only just realised i do not 100% know what is the best config for my system.

I have 2x1gb sticks and 2x2gb sticks (all the same brand, timings & voltage) and an Asus P5Q deluxe.

From the Motherboard manual:

"You may install varying memory sizes in channel A and B. The system maps the total size of the lower-sized channel for the dual channel configuration. Any excess memory from the higher-sized channel is the mapped for single channel operation."

So would i be better with:

CPU: | 1GB | 2GB | 1GB | 2GB |
or
CPU: | 1GB | 2GB | 2GB | 1GB |

I'm thinking the bottom one as it would map 3gb's as dual channel rather than 2gb, am i right in saying this?

Thanks for any help.

 

[T_T]

Your assessment is incorrect. You cannot enable dual channel with 3GB of RAM. First let's address what enables dual channel...

To achieve Dual Channel mode, the following conditions must be met:

Matched DIMM configuration in each channel
Same Density (128MB, 256MB, 512MB, etc.)
Matched in both Channel A and Channel B memory channels
OR

Populate symmetrical memory slots (Slot 0 or Slot 1)
Configurations that do not match the above conditions will revert to Single Channel mode.

The following conditions do not need to be met:
Same brand
Same timing specifications
Same DDR speed
Memory channel speed is determined by the slowest DIMM module populated in the system.

*This really depends on your motherboard. Some manufacturers use a color
-coded system (meaning use the same colors) and some require that you use the symmetrical approach (meaning same slot on both channels).

Now let's address the caveat in your mobo: "You may install varying memory sizes in channel A and B. The system maps the total size of the lower-sized channel for the dual channel configuration. Any excess memory from the higher-sized channel is the mapped for single channel operation."

What this means is that with your two kits (2x1 & 2x2), the higher density match will be "mapped" for use in dual channel (in this instance your 4GB kit), while the lower (2GB kit) will be "mapped" for single channel use.

What is dual channel and how will it affect you?

Dual channel was created to address the issue of bottlenecking that occurs at the memory controller. Bottlenecking occurs when the CPU can process faster than the RAM can supply info. In other words, when the CPU bus speed is greater than the memory speed, you end up with bottlenecks. With dual channel, the bandwith is theoretcially doubled, which would allow double the amount of data to pass through the memory controller to the CPU; technically allowing for double speed.

Despite the proclaimed gains in dual channel mode, there is arguable a 5% gain in speed. So what this means to you is that rocking mixed channels will have zero impact on your performance.

 

[Neil27]

Thanks for that explanation

so if the sticks as they are inserted in my computer now:

CPU: | 1GB | 2GB | 1GB | 2GB |
^ ^
The memory controller will be mapping the two 2gb sticks in dual channel, because the chips are higher density?

 

[Leaps-from-Shadows]

Ummm ... no.

All that complex gobbledy-beloved patriot from T_T was right ... and yet the conclusion was wrong.

You have 6GB total RAM. If you put 3GB in A1 and A2, and 3GB in B1 and B2, then the channels would both have the same amount of memory and then all of it would operate in dual-channel mode.

Neil27:
The "CPU:1GB/2GB/1GB/2GB" option will do that for you.

What the "caveat" means is if you had 4GB (2x2GB) in channel A and 2GB (1x2GB) in channel B, then 4GB would be dual-channel and 2GB would be single-channel. In essence, one of the 2GB sticks in channel A would be in dual-channel mode with the 2GB stick in channel B, and the extra 2GB stick in channel A would be in single-channel mode.

 

[Neil27]

Thanks for the input. So your saying that the fastest config for my RAM would be:

CPU: | 2GB | 2GB | 1GB | 1GB | ?

 

[johnnyq1233]

No...you need the 2GB sticks in the yellow slots...and the 1GB sticks in the black stots...
So you would go..2GB(yellow A1),1GB(black A2),2GB(yellow B1),1GB(black B2)
Now you'll have it all on dual channel mode...
That is what they mean by dual channel mode..channel 'A' + channel 'B' the color scheme helps to identify the dual channel slots...
Hope this helps....
JQ

 

[JDFan]

No...you need the 2GB sticks in the yellow slots...and the 1GB sticks in the black stots...
So you would go..2GB(yellow A1),1GB(black A2),2GB(yellow B1),1GB(black B2)
Now you'll have it all on dual channel mode...
That is what they mean by dual channel mode..channel 'A' + channel 'B' the color scheme helps to identify the dual channel slots...
Hope this helps....
JQ

Normally that is correct but according to the pic posted channel a and b in this case is actually the 2 mimatched colored DIMM (channel a is the left yellow and black and channel b is the right mismatched colors !!! -- (though that does not make sense !!) --- to figure out which is correct (whether the MOBO was put together incorrectly with mismatched colors creating a channel or the text is incorrect) will require testing by first placing the 2x1GB. Dimms in the matched color slots and seeing whether it reports as dual channel and\or then swaping them to what the text calls a channel ( the 2 left Dimm slots - 1 yellow and 1 black) and seeing if that reports as in dual channel mode --- Either the color scheme is incorrectly placed or the Text is incorrect in the manual so only way to find out for sure is to test it !!

But in normal instances to enable dual channel the 2 same size Dimms must be placed in one channel (normally matched color slots on the MOBO) -- In this instance due to an error in either the text of the manual or in manufacturing the MOBO (most likely the text in the manual) there is a lot of confusion on which is actually correct and only testing will discover which is the correct placement !!
As the Pic text is saying :
CPU: | 2GB | 2GB | 1GB | 1GB |
would be dual channel but the color scheme of the MOBO suggests that :
CPU: | 2GB | 1GB | 2GB | 1GB | is dual channel and only way to be certain which is correct is by testing !!

 

[Leaps-from-Shadows]

JDFan is needlessly confusing the issue. It does make sense, trust me. All dual-channel boards have different color slots like that. Even triple-channel boards do, and the upcoming quad-channel boards will too.

To get dual-channel mode you want the same size RAM sticks in the same color slots. A1+A2 must equal B1+B2.

You can either do:
1. CPU/1GB/2GB/1GB/2GB (That means 1GB+2GB in channel A = 1GB+2GB in channel B -- dual-channel -- Yay!)
OR
2. CPU/2GB/1GB/2GB/1GB (That means 2GB+1GB in channel A = 2GB+1GB in channel B -- dual-channel -- Yay!)

I suggest the first option.

 

[JDFan]

JDFan is needlessly confusing the issue. It does make sense, trust me.

To get dual-channel mode you want the same size RAM sticks in the same color slots. A1+A2 must equal B1+B2.

You can either do:
1. CPU/1GB/2GB/1GB/2GB
OR
2. CPU/2GB/1GB/2GB/1GB

I suggest the first option.

Actually according to the diagram he posted :

It states that the channels in this case are actually not following the color code scheme that most MOBOs follow so not sure where you say I'm needlessly confusing the issue since if this diagram is correct then to use dual channel he would need to use the 2 different colored slots to enable dual channel - so only testing will tell which method is actually the correct one ! (while it is true that normally the same colored slots make up a channel according to the diagram that is not the case with this MOBO !!)

 

[Leaps-from-Shadows]

Check out these links:
ASUS
Gigabyte
ASRock
MSI
Notice that all the boards have the same setup with alternating colors.

You're saying that it's not following the color code, but it is. You put the first set of memory in one color, and the second set of memory in the other color. Trust me. I'm pretty damn good at this stuff.

Neil27:
1. CPU/1GB/2GB/1GB/2GB (That means 1GB+2GB in channel A = 1GB+2GB in channel B -- dual-channel -- Yay!)
OR
2. CPU/2GB/1GB/2GB/1GB (That means 2GB+1GB in channel A = 2GB+1GB in channel B -- dual-channel -- Yay!)

I suggest the first option.

 

[Neil27]

Thanks for the input, 2 conflicting views on it...

Just so you know i am currently running as:

CPU/1GB/2GB/1GB/2GB

and CPU-Z reports dual channel. But to be honest I see a lot on conflicting stuff about dual channel RAM, it's so simple but somehow gets mixed up somewhere.

 

[T_T]

Good to see that all worked out for you. Dual channel is really quite simple; just match densities in any channel. But what JDFan and Leaps were arguing about is what defined the channel. In my opinion, they both had valid arguments. One can reasonbly conclude that if matching colors works for most mobos, then it should work for yours; however, in the event that wasn't true (and I've had a mobo that supports this) you would have to use (according to your manual) A1A2 as Channel A, and B1B2 as channel B, instead of A1B1 as Channel 1, etc...

 

[johnnyq1233]

That is why it is dual..channel.... channel 'A' and channel 'B' working together to give you a slight performance boost...
The color coding just makes it easier to identify the 1st pair of slots for dual channel mode.
Glad you got it so now you're in dual channel mode....