teishpa Posted February 5, 2008 Share Posted February 5, 2008 I have a P5B I would like to upgrade from 2GB to 6GB for Fedora or Ubuntu x86-64. I realize I might lose a few percent on peak memory performance, but I have some large databases to process that will benefit tremendously from the extra memory. Memory I presently have: TWIN2X2048-6400C4 DDR2-800 (XMS2-6400C4) 2GB Kit (2 x 1GB) 2.1v 4-4-4-12-2T How it is actually rated according to the Corsair PDF: Tested at latency settings (4-4-4-12) at 2.1V SPD programmed at: 5-5-5-18 at 800MHz Two upgrade options from the Corsair memory configurator: TWIN2X4096-6400C4DHX DDR2-800 (XMS2-6400C4) 4GB Kit (2 x 2GB) 2.1v 4-4-4-12-2T TWIN2X4096-6400C5 DDR2-800 (PC2-6400*4GB) 4GB Kit (2 x 2GB) 1.8v 5-5-5-18-2T The later product is presently available for a good price. The former product is marked as not yet available on the Corsair web site. The DHX also shares the curious JEDEC configuration of my existing modules. Tested at latency settings (4-4-4-12) at 2.1V SPD programmed at: 5-5-5-18 at 800MHz First question. If I decide not to wait for the DHX, is it possible to make the 6400C5 work alongside my existing 6400C4? Would I have to downgrade to 667MHz? What voltage would I use? The Asus P5B manual does not say if it regulates voltages for the two banks independently. Second question. If I decide to wait, what frequency and voltage would work best for the C4DHX alongside my 6400C4? Third question. If at some point I decide to take a small chance on stability, what tweak would I need to apply to my Northbridge to regain 800MHz operation for either of the four bank configurations I've mentioned? It's a great to have this forum. I thought it would be easy enough to figure this out for myself, but the more I read, the less clear it became. Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted February 5, 2008 Corsair Employees Share Posted February 5, 2008 I would not suggest mixing memory with any system but you are welcome to try it if you like. If you do I would suggest setting the memory frequency at DDR667 and set the memory Voltage to 2.0 Volts and set the timings manually to Cas 5-5-5-15 and TRC to 24 and write to precharge delay to 15 and test with http://www.memtest.org to make sure its stable but you also need to disable legacy USB when running any memory test on that MB. Link to comment Share on other sites More sharing options...
teishpa Posted February 6, 2008 Author Share Posted February 6, 2008 Memoryguy, thanks for the memory tweaking advice. That will prove helpful after I make my purchase. But first, I must decide what to purchase. How same? On the surface, the upcoming TWIN2X4096-6400C4DHX has identical spec. sheets specs. to my existing TWIN2X2048-6400C4 and would seem to provide better odds of passing memtest in a four-stick configuration. Is that potentially true? Same enough My idea in purchasing my first 2GB of Corsair memory was that adding another 4GB of Corsair memory a year later with the same JEDEC specs. and voltage rating would be "same enough". Now I'm finding out a year later that I basically need a matched quad 4x2GB and even then it costs me some performance to have four memory slots populated. Wow. Who patented fragile? I miss the dual Opteron server I once configured with two pairs of independent memory banks. The 8GB option If I purchase two sets of TWIN2X4096-6400C4DHX, will I end up with roughly 7.5GB on my Asus P5B? Would I have reasonable odds this would be reliable? P5B Northbridge "memory remap feature" I'm also wondering about the Northbridge "memory remap feature" that is missing from my stock P5B BIOS. Was this a feature of more expensive P5B variants, or did it become available through a BIOS upgrade? What BIOS do I need? The second screen shot in the following link shows the BIOS option I'm presently lacking: http://www.thetechrepository.com/showpost.php?p=54&postcount=2 Does this option make more memory available under Linux x86_64? Or is it not important? Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted February 6, 2008 Corsair Employees Share Posted February 6, 2008 TWIN2X4096-6400C4DHX and TWIN2X2048-6400C4 different modules based on different IC's and would be mixing memory, and some MB's most I have seen do not fair well mixing memory. But the same will apply when using 4 modules. And if you do not have the memory remap option in the BIOS it may be automatic but I would suggest asking the MB Maker to be sure. The 8GB option If I purchase two sets of TWIN2X4096-6400C4DHX, will I end up with roughly 7.5GB on my Asus P5B? Would I have reasonable odds this would be reliable? A: Yes but at DDR667 and you would need to be using a CPU with 64 Bit instructions or it will not see more than 4 Gig. And you would have to use a 64 -Bit O.S. Link to comment Share on other sites More sharing options...
teishpa Posted February 9, 2008 Author Share Posted February 9, 2008 Thanks again, Memory Guy. Based on your comments, I now have a different performance profile in mind to obtain a 6 or 8GB memory configuration at an improved performance level over my stock configuration, that should still be stable. This following link suggests there is some value to running (quasi)-synchronous (533:267) if you can't run PC6400. It reports that PC5300 is a mixed bag. Maybe a better approach is to overclock PC4300 up to the PC5300 performance bracket. Intel Core 2: Is high speed memory worth its price? The following link shows that a 333MHz overclock achieves a synchronous 667MHz DDR frequency, which is what you tell me is potentially viable with a 4 stick configuration. With my E6400/Big Typhoon, I can probably manage that on air at close to CPU stock voltage. Secrets of the i965 based Asus P5B and chipset strap uncovered. If the 4-stick configuration is not 100% at 667Mhz, I can back down the overclock to some speed below 3GHz and still be happy enough. I would not suggest mixing memory with any system but you are welcome to try it if you like. If you do I would suggest setting the memory frequency at DDR667 and set the memory Voltage to 2.0 Volts and set the timings manually to Cas 5-5-5-15 and TRC to 24 and write to precharge delay to 15 and test with http://www.memtest.org to make sure its stable but you also need to disable legacy USB when running any memory test on that MB. Yes, I've had problems with legacy USB before on a different system. Question: Would your original recommendation still apply with this strategy? (CPU=333, MEM=667, clocking downward if stability is a problem). If so, I'm happy to take my chances based on your recommended parameters. If I can't make mixed 2GB + 4GB work, I'll buy a second set of identical 4GB sticks. If that doesn't work either, I'll settle for 4GB (minus that ugly hole) unless 8GB sticks become cost effective (and my board supports them). Yes, I know about the 64-bit thing. I've been running Fedora x86_64 for over a year now. Finally, if anyone hasn't spotted this yet, I see that the newly released Memtest86+ 2.00 was "last updated" today (8 Feb 2008). Link to comment Share on other sites More sharing options...
teishpa Posted February 9, 2008 Author Share Posted February 9, 2008 At least ten characters. Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted February 11, 2008 Corsair Employees Share Posted February 11, 2008 Question: Would your original recommendation still apply with this strategy? (CPU=333, MEM=667, clocking downward if stability is a problem). If so, I'm happy to take my chances based on your recommended parameters. If I can't make mixed 2GB + 4GB work, I'll buy a second set of identical 4GB sticks. If that doesn't work either, I'll settle for 4GB (minus that ugly hole) unless 8GB sticks become cost effective (and my board supports them). A: That sounds reasonable and worth a try, but they might not work together because they are not the same part! Link to comment Share on other sites More sharing options...
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