Help me upgrade this Mac Pro!

[alevasseur14]

Hey everyone! I'm helping my landlord update his 2006-2007 Mac Pro and seem to be having trouble getting it to recognize one of the 8 GB sets as 2X4 GB. If you have all 4 4GB modules in the top riser, one pair reads 2X4 and DIMM 3+4 read 2X2. I've switched pairs around and it still reads the same. I've mixed up the pairs up and no matter what, it reads the same. Now the funny thing is this:

If I have one 2X4 GB set in DIMM 1+2, the other set will read 2X2 GB, now matter where else I put it, riser A or riser B.

I ordered modules from Newegg that matched what Crucial says the specs are perfectly and am getting pretty frustrated.

Here's the machine I'm working with:
- Mac Pro 2006-2007 with 2 X 2 Intel Xeons 2.66
- 4 X 4GB modules from Kingston 667 mhz EC (ordered by me)
- 2 X 2GB modules (Unknown, were already in the machine)
- 2 X 512 MB modules (Unknown, were already in the machine)

By my count, I should be able to get this thing up to 21 GB of memory but the highest I've been able to do is 17 GB. Don't get me wrong, 17 GB is 9 GB more than I have in my desktop but the landlord is a professional photographer and video editing kind of guy. I've followed the PDF instructions by Apple and can't get it. Help?

 

[sk560]

There is a certain way to populate the ram and the instruction is on the door.

I thought the max for that Mac Pro is 16GB. I think some company (Kingston?) claims to have 32GB running.

 

[alevasseur14]

I don't think 16 is the limit as I've already got it recognizing 17GB. Plus, I ran the Crucial Memory Scanner and it says 32 is the max, with a 4GB max per slot.

 

[lokiju]

If you put a 2GB stick in the top expansion card then you need to put another match in same slot in the bottom expansion card.

Shows it on the door.