The AMD 64 architecture, in 64 bit mode, supports a full 64-bit virtual address space with 4 petabytes of physical memory (2^52 or 52 bits) -- However the initial implementations (Opteron, Athlon FX) support 256 TB (2^48 or 48-bit) virtual memory addresses and 1 TB (2^40 or 40-bit) physical memory addresses.
The current Opteron processors, according to the AMD Functional Data Sheet
' ">http://www.amd.com/us-en/asset...nd_tech_docs/31412.pdf, support up to 8 DIMMs with a 128 bit memory interface. The maximum DIMMs can currently be 4 GB (using a stacked DIMM).
So an 8 processor board with 8 DIMM slots per processor at 4 GB per DIMM is 256 GB.
IWILL's 8P board only has 4 DIMMs per processor.
The 4GB DIMMs are REALLY EXPENSIVE, even hard to find an online qoute. Last time I looked (months ago) was in the range of $6000 to $8000 per DIMM. Maybe less today, but you'd likely quickly talk yourself out of building a system with them.