Mac Pro Memory Configurations

I wouldn't think it matters much, if you have another 2x512 sticks or another 2x2gb sticks then they should share a daughtercard.

 

Follow the instructions on the inside of the MacPro side cover

One Pair of Ram : top card ... inside pair of slots

Two Pair of Ram : top card .. inside pair of slots
bot card .. inside pair of slots

Three Pair : same as two.. 3rd pair on top card

 

Install then in descending order of size:

Your two largest go in Riser A Slots 1 and 2
Your next two go in Riser B Slots 1 and 2
Your next two in Riser A Slots 3 and 4
Last two in Riser B Slots 3 and 4


STOP READING NOW



(Ok, you just had to keep on reading, din't ya?)
Here is some nit picking detail that doesn't pertain to the original post.

The only exception might be if you have 4 of one size and 2 larger ones, it might be a smidgen faster to put the four in 1&2 1&2 for 256 bit access however -- it depends on how your programs use memory - the 3 & 4 slots are slower to access than the 1 & 2 slots, so that's why generally you want your largest memory in first, under the theory that if you can keep all or most of the memory access in 1 & 2, you won't have the additional latency of 3&4

Thanks
Trevor
CanadaRAM.com

 

This should help.
However, when using different sizes Apple recommends that you install the
larger size in the first two slots on riser A and the smaller in the first two slots
on riser B.

In your case, you would install the pair of 2Gb sticks in the first two
slots on riser A and your pair of 512's in the first two slots of riser B.