My Mac Pro (3,1) came with 2GB and have upgraded in the past with 8GB for 10GB (no problem). I just bought a 4GB RAM set but it only shows as 12GB. I thought the RAM was defective and had it replaced but still have the same problem. I have it set up as follows. Riser A 2GB+2GB, 2GB+2GB: Riser B 2GB+2GB, 1GB+1GB. This follows the Mac Pro install chart. Is there a problem using 1GB (2) RAM on Riser B with 2GB RAM on Riser A (it worked fine with 10GB)? Is it not possible to show 14GB because of this?