Q:

How is multiprocessing related to cores and threads?

I am interested in the Intel Xeon E5-1650 v3 and the Intel Xeon E5-2643 v3 processors. They both have 6 cores and a clock speed of ~3.5GHz. However, the specifications from CPU-world (screenshot) show that the Intel Xeon E5-2643 v3 processor has 2 multiprocessing units as opposed to 1 for the Intel Xeon E5-1650 v3. I am aware of what the difference is between cores and threads, although I am confused why one of the processors has 2 multiprocessing units and the other only 1.  What does this mean in practical terms?

A:

The "Multiprosessing" in this case refers to Symmetric Multiprocessing (SMP).
This is when you have more than one physical processor on the motherboard.
The first number in the second section of the Intel model number tells you the maximum SMP configuration the processor can be part of.  So for example, E5-1650, it's a "1" and with E5-2643 it's a "2".
The E5-1650 cannot be used in an SMP configuration, and the E5-2643 can be used in an SMP configuration with (up to) 1 other processor (2-way SMP), and something like the E5-4620 can be used with up to 3 other processors for 4-way SMP.
Here's an link to a comparison of these three CPU's at Intel's ARK (see the line titled "Max CPU Configuration"):
http://ark.intel.com/compare/85758,81900,82765

