Dual channel Question

[silverferro]

I have K7N2 Delta2 LSR board and have 3 memory slots only. At the moment I have 2 256MB DDR modules on each channel(256MB on purple slot 1 and another 256MB on green slot).

Now I want to upgrade my memory and my plan was to fit both 256MB modules on one channel(fill up both purple slots with 256MB each) and buy another single 512MB and install it on the other channel(green slot). So that both sides have equal capacity for dual channel to work.

But when I went to buy the 512MB module the shop keeper tells me this method won't work for dual channel since both modules need to be identical capacity to work.So he suggests I get 2 512MB modules for each channel and remove the 256MB. This does not make sence to me,as whats the purpose of having 3 slots when only 2 can be used.I belive the shop keeper is trying to con me into buying more from him.

Please advice if the method I suggested will work or is the shop keeper correct? Thanks

 

[deathwalker]

no, you will not run dual channel with the 3 sticks of memory.

 

[leigh6]

Here is your manual.

http://www.msi.com.tw/program/support/m.../mnu/spt_mnu_detail.php?UID=617&kind=1

According to the manual in order to run dual channel you must only use 2 slots. MOST likely they have to be the same size and speed.

 

[silverferro]

ok thanks

 

[cwos]

I'm pretty sure that for dual channel you would put a module in each of the two purple slots. They need to be the same size and preferably the same manufacture. As for the green slot, this wont be involved with any dual channel because there is only one. I don't think the green slot will work if the others are in dual channel mode. Maybe thats what the shopkeeper meant. Is any of this mentioned in your motherboard's manual? eg. if the green slot will work while the purple ones are in dual channel.
Hope this helps

 

[silverferro]

Oh man so i'm stuck with 512MB of 2x256MB modules?...thanks guys for clearing things up. Just one more thing, qurious to know if I install each 256MB on each channel (one purple slot and green slot) dual channel works right.... like what I have now. What will happen if I install a 512MB on the remaining slot? Will the whole dual channel thingy stop working or will the dual channel work with the 256MB modules and the 512mb will work on its own and giving a total of 1GIG system memory?thanks again.....

I have posted on so many different forums before but this is the 1st time I have gotten a reply this fast.Alomst instantly like I'm talking on irc. AnandTech community rules....

 

[YOyoYOhowsDAjello]

Just to go against the grain, I have personally witnessed a system with 2x512mb and 1x256 that started up and detected all ram installed and said it was running in dual channel mode.

Wasn't my system and I didn't do any testing on it, but it was stable and everything.

 

[silverferro]

Thanks for the reply CWOS....My manuel says for dual channel to work the slot 1(purple) and slot 3 green or slot 2(purple) and slot 3 green should have the same modules. But I don't understand whats the purpose of the 3rd slot if it can't be used. MSI just added one more for show since there was extra space or to make it sound better on the box under specifications since 3 is better then 2....

Thanks for ur input YOyoYOhowsDAjello

 

[Lord Evermore]

The nforce2 chipset does not use memory the same way a dual-channel Intel chipset does. The data is not exactly "striped", the two channels are independently accessed to provide lower latency memory access. While one channel is actually returning the data that has been requested, the second memory controller can be issuing a request to the other channel, so that the CPU will immediately begin receiving that data, rather than working in a "request, receive, request, receive" pattern.

Because of this, the two channels do not have to be matched sizes. They don't have to be the same speed ratings either, but of course they will both run at the speed of the slower module.

If you wanted, you could install a 512MB module in channel 1, and a 256MB in channel 2. The first 256MB of each channel would be addressed with the performance enhancements of dual-channel. However the upper 256MB on channel 1 would always perform as if it were single channel. So depending on the amount of data you have in memory, and where it ends up being stored, some of your data would be accessed with the reduced latencies possible with nvidia's dual-channel, and some might not.

An analogy would be this: two men with troughs. One trough is 10 gallons, the other is 15 gallons. You're handing them pingpong balls with various numbers on them (you're acting as the CPU and memory controller). You decide you need ball #10, so you request check and see man A has that ball. He grabs it from his 10 gallon trough. While he's handing you that one, you ask Man B to give you ball #12. You've saved a little bit of time because you didn't have to wait until Man A gave you the first pingpong ball. But now, you discover that you also need ball #13, which is in Man B's trough. So you have to wait until he gets you the one you already requested, before you can ask for another. This illustrates how sometimes the latency is NOT reduced using this memory design. However it is not any worse than normal latency, and sometimes is better than single-channel. The Athlon XP frontside bus can't make use of larger bandwidth, so using dual-channel the way Intel does is not efficient. Lower latency helps more.

Now, to show how the larger trough (different module sizes) can work: you have 21 gallons worth of pingpong balls. So you fill up Man A's trough of 10 gallons (balls #1 to 100)and give 11 gallons to Man B (balls 101 to 110). Suppose you find you need balls 101, 102, and 103 all in a row. Well you have to ask Man B for them one by one, and never to get make use of the time savings with Man A retrieving balls for you. But you do still have those balls stored, and they're being retrieved just as fast as you can ask Man B for them. Then at random times you find that Man A does have a ball you need, so you cheer and ask him for the ball while Man B is still pulling one out for you.

In silverferro's case however, both channels could have 512MB in it and run in dual-channel mode. The two purple slots are assigned to channel 1, and the black slot is channel 2. With the two 256MB modules in the purple slots, they make a total of 512MB in channel 1, so that the two channels have equal amounts of memory.

This is all different from the way Athlon64 and all Intel memory layouts work.

 

[silverferro]

Thanks alot Lord Evermore for giving such a clear and long post. thank you very much. so it will work as i thought. shall try it out. thanks to every one who posted also.