[dboreham]

You can build motherboards with two or more completely isolated sets of CPU and memory, that are physically compatible with standard racks etc.

[Bluecobra]

Good point, I forgot about those. It would be interesting to see if 1x PowerEdge C6525 with four single processor nodes is cheaper than 2x Dell R7525 servers. The C6525 does support dual processor, so it does seem a bit wasteful to me.