Xserve

Quad-Core Intel Xeon “Nehalem” processors.
The new Xserve Quad-Core Intel Xeon “Nehalem” processors deliver outstanding performance through an enhanced microarchitecture, integrated memory controller, and two new features: Turbo Boost, which dynamically speeds up the cores in use when others aren’t needed; and Hyper-Threading, which allows two threads to run simultaneously on each processor core.

Unlimited-client Leopard Server.
Xserve ships with Mac OS X Server v10.5 Leopard, which supports an unlimited number of Mac, Windows, Linux, and UNIX clients. Powerful client management services and new Leopard Server features make Xserve the ultimate server for Mac and mixed-platform workgroups.

Improved energy efficiency.
Xserve works hand in hand with Mac OS X Server to maximize energy efficiency. The active cooling system intelligently manages fan speeds. The high-efficiency power supply (89% average) makes the most of its energy use.