Wanted: Mac Pro Ram purchase and placement advice

[wizb98y]

I plan to add memory to a 2008 3.2 Ghz 8-core mac pro that comes
with standard 2x1GB (2GB) sticks. My original plan is to buy
2x4GB sticks so that I have a total of 10GB. With this I would
have to place the memory in two ways:

Config 1:
Riser A: 4G 4G XX XX
Riser B: 1G 1G XX XX

Config 2:
Riser A: 4G 4G 1G 1G
Riser B: XX XX XX XX

According to the benchmarks at macsales.com
http://eshop.macsales.com/Reviews/Framework.cfm?page=/Benchmarks/macproearly08ram/article.html
Memory performance for both config1 & 2 will be bad.
So what to do. Should I just buy 4x2G sticks instead of
2x4G sticks to get:

Config 3:
Riser A: 2G 2G 1G 1G
Riser B: 2G 2G XX XX

for better performance. My preference is to only buy 4G sticks
and have extra free slots for future memory expansion but is
concerned with getting poor memory performance in the meantime.
Recommendations and comments?

 

[-js-]

Configuration 1 is what you want. You can't have all four DIMM's only on the top riser. And you are right to only want to buy 4GB DIMM's. It's just the best idea for future memory expansion. And while the highest throughput may be with all 8 slots filled, you increase latency. The magic number of DIMM's is 4, from what I've read on anandtech.

BUT . . .

It really doesn't freaking matter. Getting the 4GB highest density FB-DIMM's is far more important. And having enough memory is far more important. A few nano seconds of extra latency is nothing compared with having a page swap to disc.

FWIW, I bought a 2008 MP with 2x1GB and added 2x4GB, just like you plan to do. I moved one of the 1GB DIMM's down to join the other 1GB DIMM, and then put the 2 4GB DIMM's in slots 1 and 2 of the top riser. OWC has a nice instruction sheet that they provide with their FB-DIMM's.

10GB is awesome, BTW! You'll love having that much RAM, if your usage patterns are anything like mine.

 

[wizb98y]

Thanks for the advise.
I think you pushed me over to settle on the 4GB sticks.
Maybe I'll just buy 4x4GB sticks. It is just money