[0] - http://ark.intel.com/products/family/78583/Intel-Xeon-Proces...
[1] - http://ark.intel.com/compare/?ids=85766,85765,85764,85763,85...
E3/E5/E7 (market segment + socket), the first digit is the socket configuration (2/4/8), the next 3 digits are a model number and the vX at the end is the CPU generation.
The Xeon E3-1220v2 in my ProLiant ML10 is a lower-end, single socket Xeon in a fairly high performance segment.
The Xeon E5-2403v2 in my ThinkServer TD340 is a mid-range, dual socket Xeon in a fairly low performance segment.
The fact that the 3 digit identifier has no relation to overall performance is the biggest shame in the Xeon chips, considering Intel does this with the Core i3/i5/i7 products.
OTOH, Xeon's can vary so wildly it's hard to give a tangible performance or configuration metric to the model identifier. Things like overall CPU cache, core count, clock speed, expansion support (namely, number of PCIe lanes) all vary so much that you really have no choice but to look at ARK since there's no way to convey this in a more efficient manner.
EX = product line
vX = generation
The clock speed omission is a bummer, but Xeons have two different clock speeds on all processors (one turbo -- which only a certain percentage of the cores can hit simultaneously), so things are a bit more complicated.
[1] https://semiaccurate.com/assets/uploads/2011/04/xeonmodels.p...