Why must DIMMs be installed starting with the lowest number first?

[Crazy_Insane]

Hey all, first post here so sorry if it's in the wrong section. It's not really an Intel exclusive topic but it's the most suitable forum that I could see.

Anyway, why is it always recommended to install two sticks of RAM in a certain order?
Eg, "For optimum performance, when enabling Dual Channel mode with two memory modules,
we recommend that you install them in the DDR3_1 and DDR3_2 sockets."

I get the difference between single and dual channel but why can't you install the sticks in DDR3_3 and DDR3_4 (blue) sockets?
Why does it have to start with the lowest number first?

Thanks for any replys, I haven't been able to find the answer anywhere.

[MarkJohnson]

Channel 1 and 2 are the primary on the controllers.  These have two controllers with each controller having 2 channels.  The want the primary channels as they are designed that way.

However, I've used the secondary successfully every time.  The aftermarket CPU coolers block the first channel on older boards (slot closest to the cpu) and newer boards have moved them to the slot furthest from CPU for added heatsink clearance.

But as I've said, I've never had an issue ever.  I know some MB makers create custom motherboards and may have issues?

-=Mark=-

[Dark Mantis]

Just to add to what has already been said by MarkJohnson the primary slots were originally put closest to the CPU as they were physically the closest and therefore the fastest. Although this difference is minute it was considered worthwhile.