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
The 3000 series, codenamed Conroe (product code 80557) dual-core Xeon (branded) CPU, released at the end of September 2006, was the first Xeon for single-CPU operation. The same processor is branded as Core 2 Duo or as Pentium Dual-Core and Celeron, with varying features disabled.
They use LGA 775 (Socket T), operate on a 1066 MHz front-side bus, support Enhanced Intel SpeedStep Technology and Intel Virtualization Technology but do not support Hyper-Threading. Conroe Processors with a number ending in "5" have a 1333 MT/s FSB.The 3100 series, codenamed Wolfdale (product code 80570) dual-core Xeon (branded) CPU, was just a rebranded version of the Intel's mainstream Core 2 Duo E7000/E8000 and Pentium Dual-Core E5000 processors, featuring the same 45 nm process and 6 MB of L2 cache. Unlike most Xeon processors, they only support single-CPU operation. They use LGA 775 (Socket T), operate on a 1333 MHz front-side bus, support Enhanced Intel SpeedStep Technology and Intel Virtualization Technology but do not support Hyper-Threading.