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Add TWIN2X4096-6400C5C to existing TWIN2X2048-6400C4?


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Hey all,


I've got a system running 2GB of Corsair DDR2-800 memory (TWIN2X2048-6400C4) under Windows Vista 32-bit, and I'm looking to upgrade to Windows 7 64-bit later this week when it becomes available to my company through MSDN. I want to add some more memory to take advantage of the 64-bit OS, but have a question about compatibility.


I'd like to purchase 4GB more of Corsair DDR2-800 (TWIN2X4096-6400C5C). Can I simply add this to my system, populate all four DIMM slots and get a total of 6GB? In order to do so on my motherboard (Asus P5W DH Deluxe), I know that the memory will have to run at 667 MHz, but that is fine because that's where my existing 6400C4 RAM is running. I'm not overclocking at all.


Presently, I have my 2GB of 6400C4 RAM running a 4-4-4-12 (EPP), and my DIMM voltage is set at 2.1V. The system has been stable like this for almost three years. Since the 6400C5C is not rated for this, I'm planning to drop down to 5-5-5-18 and 1.9V on all banks. Will that work OK?


Frame of reference: I used to game on this box, but now I just do work. Large image editing and web development for the most part, although I occasionally play a classic favorite like System Shock 2 or Doom 3. Not really anything modern.


If anybody has some tips for me on this RAM upgrade, feel free to share.

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It probably won't work. First of all, mixing memory types is not good practice, and second, populating all four memory banks is extremely chancey (look around here and on the mobo manufacturer's forum for many hair-pulling stories <mine is one> about trying to get all four memory banks to work, even when using matched memory modules. Yes, it can be done if you're lucky and have the time and ability to tweak the BIOS as a hobby, but just about everything I've read recently advocates against it. If you're determined to try, the best thing would be to get four 2GB modules of matched type (2 sets of 2 matched modules) from a vendor that has a very liberal return policy. Either that or wait for a certain other manufacturer to start making 4GB modules again and get two of those. Needless to say, YMMV.
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Thanks for the info! Yeah, I've heard some horror stories. I too tried filling all four DIMM slots once before, with four 1GB sticks of the same Corsair 6400C4 I have now, but had problems (only half of the RAM was recognized). As soon as I took one stick out, everything was OK. In the end I returned the second pair and stuck with the pair I have now. I was never quite sure if it was the RAM itself or the board; didn't mess with it long enough to find out.


My motherboard doesn't support DIMMs larger than 2GB either, so 4GB modules, even if available, wouldn't help me.


I've done my fair share of tinkering with BIOS settings, and will be doing a fresh reinstall of my OS anyway, so I will probably give all four DIMMs a try just to see how it goes. Got nothing to lose.


Worst-case, I will stick with the pair of new 2GB 6400C5C sticks for a total of 4GB. It's certainly better than 2GB! :)

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