09 Mac Pro Memory Upgrade Question

Yes.

Yes.

Neither configuration is ideal (not balanced in terms of capacity), but they will work. For further clarification as to how/where you should place the DIMM's, take a look at the DIMM Replacement instructions (page 4).

 

You only have RAM on a single memory controller. So for the second CPU to get access, everything has to be passed over the QPI interface between the CPU's.

The kit only has 3x DIMM's in it. So it would be impossible to make it work in 4x slots.

Unless you already have another 4GB stick on hand or will purchase it (buy 4x 4GB Sticks).

Now there's another note you need to be aware of if the memory is being bought from OWC; their 4GB sticks don't mix with the OEM memory, so you'd want to make sure they're all on one CPU, the OEM on another (1GB sticks, as you seem to be interested in doing). This keeps them on separate memory controllers (one in each CPU).

 

I have the same 2009 2.26Ghz 8-core MacPro, and buy this 215$ Crucial Memory kit
http://www.crucial.com/store/partspecs.aspx?imodule=CT2KIT51272BV1339
Put each 4GB stick on socket 1 of each memory modules and now have 14GB of Ram, 15 days no problem at all and making a full 13 episode animated series in after effects and Premiere Pro, no hangs!!

Cheers

 

Triple channel is useless to most people, as their software can't take advantage of it (doesn't work in a manner that will utilize the additional bandwidth). Which is why capacity tends to trump memory bandwidth for most users.

The exceptions would be things like scientific/engineering simulations for workstation use.

But application suites such as CS5 or similar, do not fall into this holy grail of software. Fill the slots if you need to for capacity reasons, and be done with it.