Quick question on adding RAM

Depends on the board, what motherboard do you have?

Many can run 768x2 in dual channel (512+256, 512+256 DC), of course this depends on the board.

My Desktop: <A HREF="http://Mr5oh.tripod.com/pc.html" target="_new">http://Mr5oh.tripod.com/pc.html&lt;/A>

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

www.crucial.com
The Memory Experts(SM) at Crucial Technology is now on board to give you straight answers to your memory-related questions.
cpl@micron.com

Also keep in mind, you may see a preformance drop with all 4 slots filled...it is better to have a lesser amount of slots taken up. That way there are fewer memory buses for the cpu to access

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AMD Athlon 64 3500+ (stock)//1GB Corsair 3200XL//ATI Radeon 9700Pro (360/335)//WD Raptor 74GB/Antec Neopower 480W//Lian Li PC-61 Custom

Thanks for the quick replies!

I have an intel 865gbf motherboard with, as I said, 4 available slots.

Thank you again!

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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Crashman is absolutely correct. I posted a topic about this earlier but there were no good responses.

The answer, though it is not explained too well, is found at (look at the last page):
ftp://download.intel.com/design/chipsets/applnots/25273...

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)
OR
For a single DS (double sided) DIMM occupying a channel,
A[19] is used for rank selection
A[20] used for regular row address bits on the memory bus.

For two DS DIMMS occupying a single channel, both A[19] and A[20] are used for rank selection.
This configuration offers faster performance.