For those of you who are purchasing a new Mac Pro Octo Core and planning to upgrade your RAM after the purchase, be aware that Apple's instructions on upgrading are actually wrong.
In my case, I purchased an Octo Core 3.2 with the minimum 2GB RAM and ordered an 8GB Upgrade Kit from Crucial. This consists of 2 sticks of 4GB each. According to Apple's instructions, if you have the standard 2GB RAM configuration (1GB on each Riser) you should install the next pair of RAM equally on each Riser.
So I placed a 4GB stick on Riser A and a 4GB Stick on Riser B. That didn't work. The machine still showed 2GB RAM and all the other memory slots empty. So I contacted Crucial using their handy dandy "live chat" service to speak directly with a support agent.
He told me to move the Apple installed RAM to Riser A and the Crucial RAM to Riser B. Did that, and voila! I have 10GB RAM now showing up in the machine. Just a note for you folks out there and kudos to Crucial for such a handy dandy live chat service. Got me up and running again in less than a minute. Yay!
Digg it
Oh... Sticky Area
You just hit the sticky are of FCP.
Here's what I have learned and while attending NAB others have agreed. FCP works best with multiples of four - 2, 4, 8, 16. Anything else can cause issues that can happen for each machine - while other machines will not see any issues with odd sizes.
Apple did write up a tech doc about this when the Intel Quads came out and the same still applies. I'm sure that it has to do with the architecture of the Intel chips and the way the system boards now work. But Apple states having same sizes across risers. Anything else will cause FCP trouble.
We have a Quad and an Octocore both built this way and we've never seen issues with memory since.
4GB is the magic number
FCP works best with multiples of four - 2, 4, 8, 16.
Yes, but keep in mind that 4GB is the number causing the issue. Not 2, not 8, it's 4. So using your theory, 4GB should work, but it does not.
You're right...
There has been more issues with computer at 4 gig than anywhere else.
But... if you going to spend alot of money on a new system, you should get at least 8 gig of RAM on the Octocore (probably not Mac memory because its so expensive but from a well established memory company).
I've been told by Apple folks and folks that used the testing systems that you should really have 1 gig per core to operate efficiently.
I'm not sure if that's an absolute but all of our Mac Pros have at least 8 gig. It's not uncommon to have FCP, Motion, Photoshop, Entourage (email), and Safari open all at the same time.
Having your memory all from the same manufacturer can make a real difference in performance related issues, too.