http://www.anandtech.com/show/5553/the-xeon-e52600-dual-sandybridge-for-servers

Intel’s Sandy Bridge architecture was introduced to desktop users more than a year ago. Server parts however have been much slower to arrive, as it has taken Intel that long to transpose this new engine into a Xeon processor. Although the core architecture is the same, the system architecture is significantly different from the LGA-1155 CPUs, making this CPU quite a challenge, even for Intel.