Xeon
Introduced in May 2013, Xeon E3-12xx v3 is the first Xeon series based on the Haswell microarchitecture. It uses the new LGA 1150 socket, which was introduced with the desktop Core i5/i7 Haswell processors, incompatible with the LGA 1155 that was used in Xeon E3 and E3 v2. As before, the main difference between the desktop and server versions is added support for ECC memory in the Xeon-branded parts. The main benefit of the new microarchitecture is better power efficiency.
Xeon
Introduced in September 2014, Xeon E5-16xx v3 and Xeon E5-26xx v3 series use the new LGA 2011-v3 socket, which is incompatible with the LGA 2011 socket used by earlier Xeon E5 and E5 v2 generations based on Sandy Bridge and Ivy Bridge microarchitectures. Some of the main benefits of this generation, compared to the previous one, are improved power efficiency, higher core counts, and bigger last level caches (LLCs). Following the already used nomenclature, Xeon E5-26xx v3 series allows dual-socket operation.