Some facts:
1. Athlon 64 processors do not support a multi-processor configuration. This is because A64 does not have the coherent hypertransport link required to address x additional processors
2xx, 4xx, 8xx Opteron processors do support multi processor setups (the 1xx series do not). Those would be the processors required.
2. Multi processors are not designed for redundancy (sorry Mucks!). They are designed to handle multi-threaded and multi processor AWARE applications.
Especially in clustered environments. The redundancy is in the network load balancing, not in the chassis or processor configuration.
MPS aware applications take longer to develop and do tend to cost more as more programming thought has to be put into splitting threads & processes over the additional processors. Common examples include adobe photoshop, adobe premiere, microsoft exchange and (funnily enough) any Quake III engine powered game.
Multi-processor AMD systems require registered memory to function correctly. This provides the higher level of error checking and correction that is needed when addressing two processors and their respective clock cycles. There are true SMP systems which have an even split 50/50 over both processors (or 25/25 in a quad setup). Numa systems make one processor the "control" processor and it will address the memory on behalf of all other additional processors. This feature allows cheaper chipsets.
The most important and pertitent information related to SMP is that unless your applications are MPS aware, it will only address a single processor. The other will sit idle. With most domestic and commercial software NOT being MPS aware, they are effectively (as pointed out) useless to the average home user. Video editing?? Only if its aware, if not, it's a waste of money with two or more.
Now some of us... can use them.. I love my dual opteron. I use Visual Studio .net to compile C# applications, run a local MySQL server as just two examples of real SMP aware applications.
Long post, can go into even more detail if anyone wants to know more...
