Optimum "slotting" when adding new RAM in Mac Pro?

I've been reading about adding RAM and have found out that in addition to adding in pairs you should also put the best/largest RAM in the first slots. But I also read that you want to have identical RAM in all 4 slots that work together (the first two slots on each card) to get maximum speed.

I have a feeling I should ignore the second suggestion since I have four 1gb modules and am planning on adding two 4gb modules to the mix and I'm assuming that I want the two 4gb in the first slots then the four 1gb in the next slots.

Would this be the optimum way to do it? I don't think I want to add four 2gb since that would fill all my slots and I think it best to keep a couple open in case I see that I could use more RAM later. Price is only $10 difference for either configuration.

Model Name: Mac Pro
Model Identifier: MacPro3,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 3 GHz
Number Of Processors: 2
Total Number Of Cores: 8
L2 Cache (per processor): 12 MB
Memory: 4 GB
Bus Speed: 1.6 GHz

Memory Slot info in attachment pic.

I also attached pic from the user's manual just to confirm the slot order.

I figure I'll end up with this (assuming Riser A is the top card):

DIMM Riser A/DIMM 1 - 4gb
DIMM Riser A/DIMM 2 - 4gb

DIMM Riser B/DIMM 1 - 1gb
DIMM Riser B/DIMM 2 - 1gb

DIMM Riser A/DIMM 3 - 1gb
DIMM Riser A/DIMM 4 - 1gb


TIA for any help.

Another thing to remember is to use the same speed memory - or the OS will use the slowest Ram for all installed memory.

Chilbear said:

Another thing to remember is to use the same speed memory - or the OS will use the slowest Ram for all installed memory.

Click to expand...

Okay, thanks. I found same specs except for 4gb modules instead of 1gb at a couple different sites.

"Premium Certified HyperVelocity™ DDR2-800 (PC2-6400) ECC FB-DIMM Modules "

or