I just have a real quick question regarding some RAM that I just purchased, 1 gb ddr400 (2X512 MB) to run in dual channel mode. Can I add this to my existing RAM, 512 MB ddr400 (2x256 MB) already running in dual channel? I have enough slots, I was just wondering if this was feasible in dual channel mode. It would be no big deal just to remove the existing RAM, but I would be very pleased if I did not have to.
Sure you can do this. As long as the motherboard has 4 slots and all the memory has the same specs. You need to make sure you install the new ones in slots 1 and 3 then install the old ones in slots 2 and 4. After this the system will be running in dual channel module with all four modules.
Crucial Performance Lab
The Memory Experts(SM) at Crucial Technology is now on board to give you straight answers to your memory-related questions.
Anandtech tested several configurations with the i875P and showed the chipset performs BETTER with MORE BANKS of RAM!!!
All in dual channel:
Worst: 2 single sided modules (2 bnaks)
Better: 2 double sided modules, 4 single sided modules (4 banks)
Best: 4 double sided modules (8 banks)
So according to Anandtech the system will perform better with more modules installed.
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To Sum it up:
Basically, for the i875P chipset the Memory Controller Hub configures the memory address lines differently for a given arrangement of DIMMS in the slots:
For two SS (single sided) DIMMS occupying a channel (2 slots/channel)
For a single DS (double sided) DIMM occupying a channel,
A is used for rank selection
A used for regular row address bits on the memory bus.
For two DS DIMMS occupying a single channel, both A and A are used for rank selection.
This configuration offers faster performance.