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Quick question on adding RAM

Last response: in Memory
October 26, 2004 6:40:16 PM

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.

Thanks guys, sorry for the newbie question,
October 26, 2004 8:23:20 PM

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.

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October 26, 2004 9:12:34 PM

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

AMD Athlon 64 3500+ (stock)//1GB Corsair 3200XL//ATI Radeon 9700Pro (360/335)//WD Raptor 74GB/Antec Neopower 480W//Lian Li PC-61 Custom
October 26, 2004 9:26:23 PM

Thanks for the quick replies!

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

Thank you again!
a b } Memory
October 27, 2004 12:17:03 AM

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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October 27, 2004 11:46:05 PM

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):

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[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.