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Mixing ram?

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boostm3

Registered
Joined
Mar 18, 2007
IM currently using CORSAIR XMS2 1GB (2 x 512MB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory .

My Biostar 550 mobo has 4 ram slots, and I thought I would have a 2 x 1gb module of the same ram type as above to give me a total of 3 gb ram.. But, Corsair says NO NO... They say I should NOT mix the different sized modules, even though the ram is the same kind... They say I should ONLY add 1 more of what I have above, giving me a max total of 2 gb.. If I want more than 2 gb memory, Id have to buy 2 2x1 gb modules.. NO mixing. I thought as long as I stayed with the same ram type, speed, etc, Id be fine.. Im very surprised.. Does everybody agree that, if you have one of your two ram channels filled, you can only populate the second ddr2 channel with exactly whats in channel 1, not just in terms of ram type and mfg, but in terms of Quantity too??

Edit*** Since I wrote this, Ive learned that Corsair seems to Always give out this advice, but the truth seems to be that on the newer 64 bit boards with DDR2 ram channels, while it IS best to use the same type of ram in both channels, its NOT necessary to stay with the same module Size. ie, it should be fine to mix a 1gb ddr2 module in channel 1, and a 2gb ddr2 module in channel 2, so long as the ram type, speed, timings, and mfg are the same for each channel.
 
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Super Nade said:
I forsee no problems in general, if all four slots are populated by modules with the same SPD.

Thanks for the response.. But, if both channels are populated by modules with the same SPD, then what I wanted to use wont work.. That is, even if the same chips are used and the memory type is identical, the fact that one channel has a 1gb module populated by 2 x 512mb sticks, and the other channel has a 2gb module populated by 2 x 1gb sticks, the SPD will not be the same because the module size will be different.. Other than that, the sticks are the same, both containing Corsair PC2-6400C4 ram. I had no idea the quantity of memory in each of the two channels had to be the same.. I knew that both slots within Each channel had to contain the same quantity, but I thought the two channels themselves were somewhat autonamous.

This means that, if I want to leverage my current 1gb of ram, I can only buy 1 more gb of the same ram, giving me a total of 2gb. IF I want more than a total of 2gb ram, I basically need to throw out my current 1gb (2 x 512mb) module, and buy two new 2 x 2gb modules (4 x 1gb sticks).

This is what im being told from Corsair:

"Dear Valued Customer,

Adding 2 x 1 GB modules to your existing 2 x 512MB will most likely not be stable and is not recommended. The ICs used for the 512MB modules are different from the ones that are used in the 1GB modules. In order for the system to be stable all the RAM needs to be in sync, and all the ICs on the RAM need to be exactly the same. Since the ICs are not exactly the same on these 2 different sets of modules, there may be instances where the RAM gets out of sync (even if it is in milliseconds) and this can cause errors and crash your system. It is NOT recommended to mix and match any modules together on this platform as it can cause many problems. My suggestion would be to add only what you currently have in your system to the exact part number or replace all the modules with new ones. Sorry about that."
 
i have a stick of ultra 3200 and a stick of ultra 2700 both are 512mb and i have NO problems

they are ddr not ddr2 so im not sure if there is a problem for ddr2
 
To Boostm3,

What ever you do, don't feel like the lone ranger--I too got exactly thats same advice on the corsair forum---even with forum titles like how corsair ram is LIKELY to behave in your computer---and their first rule seems always to never mix ram---which is not all that bad with a new build---but such a rule fails miserably in the real world and for quite a variety of reasons.

But it seems to boil down to I am on my own---try it and see if it works--and since my new ram arrived---I am about to do that.

As an edited in update some eight hours later---I had to run through at least six various different bios permutations before I got something that made forward progress---as far as I can see there is little science in it and a lot of trial and error---but still sneak up on it is a rule.
 
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As OSage mentioned, you could try and see if the mix-match works. Corsair are right about that though, different chips = funky stuff.
 
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