While comparing Intel Xeon E5 and E7 processors, I've noticed that E5 processors are specified for 2S or 4S scalability, while E7 processors are specified for S2S, S4S, or S8S scalability.
I understand that the processors are specified for use in up to the given number of sockets on the same motherboard, but what does the extra S actually mean? What's the difference between 2S and S2S, and between 4S and S4S?
Best Answer
The difference between S4S and 4S is the number of QPI-Links. 4S has 2 links per CPU, S4S and S8S have 3.
On a 4S system CPUs form a ring, which means for every CPU there is another CPU with which it can only communicate indirectly, because it is only connected to 2 CPUs via QPI.
On S4S every CPU is directly connected to every other CPU.
For S8S there are also 3 QPI links.
Question is a little older, but maybe my answer is still relevant.