I own an old Asus P4C800 Deluxe mobo with 2x Corsair Twinx CMX512-3200LPT rated 2-3-2-6-T1 according to the sticker on the memory.
These sticks were installed in the blue channel in order to run in dual channel mode.
I've just purchased some extra RAM as it will be another year or so before I can afford a true upgrade - this is just to bridge the gap. The RAM I bought is some OCZ 2x1GB modules which I have installed into the black channel. The modules I purchased can be seen here:
From my understanding, modules have to be in matching pairs if they are to be run on the same channel.
And now to the problem; the system recognises the RAM but according to memtest+ it is clocking it at ddr266 rather than ddr400 and there is a big drop is the mb/s bandwidth. Running my corsairs on their own provides 2485mb/s at ddr400, while the OCZ's on their own provides 2550mb/s at ddr400. I tried using the SPD settings and I tried manually setting the cas latencies to match the corsair or to match the OCZ. Unfortunately, this did not help.
I read in the FAQ:
"The only potential problem: Because you are using 4 memory modules, which require more power, your system may clock the speed of the modules down to maintain stability."
To test this theory, I installed the ocz and then one of the corsairs (as I assume three modules would use less power than 4). They still ran at ddr266. Next, I tried using one corsair and one ocz. Again, they still ran at 266 - so I don't think it could be a lack of power, though I am not 100% sure. My PSU is around 465W and has always served me well.
Is there anything I can do to get these two to behave nicely together? They are both DDR400 and when set to a cas latency of 2.5 (a number lower than both are specified) they should be running at DDR400.
If I can't get this to work, I can only assume that I will have to sell the Corsair modules and buy an extra 2gb's of OCZ!
More about :mixing twinx corsair ddr400 ocz ddr400 underclocking
Just to help out anyone that has this problem, I thought I would post my solution.
As it turns out, with the 2gb OCZ installed, I proceeded to look through all the overclocking settings in order to see if I could squeeze a little more juice out of the system. From the CPU Jumperfree menu, I found an option that lets you manually set the speed of the memory (266, 333, 400 etc). I planned on using this to manually set the speed of the memory when the OCZ and my old Corsair memory are both installed in the system.
The funny thing is, I didn't need to do this in the end because I just put the memory back in at it was working at DDR400 straight away!! This is despite removing and reseating them several times in different banks the previous day!
Anyway ive got the system up and running at 2-3-2-6 timings and standard FSB and memory speed. I'm surprised I didn't get any posts for help but I guess this stuff is pretty old hat now so people are more interested in the new stuff!