Quoting from the AMD official announcement:
AMD today introduced the Quad-Core AMD Opteron processor, the world’s most advanced x86 processor ever designed and manufactured and the first native x86 quad-core microprocessor. Designed from inception for the most demanding datacenters, Quad-Core AMD Opteron processor-based servers from global OEMs and system builders can deliver breakthrough capabilities to customers in a time of dramatically escalating performance-per-watt emphasis.
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Quad-Core AMD Opteron processors with Direct Connect Architecture excel in virtualized environments because of the integrated memory controller4 for reduced memory latency, and Rapid Virtualization Indexing, a new AMD innovation in AMD Virtualization technology designed to reduce the overhead associated with software virtualization. Rapid Virtualization Indexing takes functionality that was previously performed in software and greatly accelerates it by performing those functions within the CPU to help enable near-real time application performance…
Rapid Virtualization Indexing is AMD implementation of nested tables technology virtualization vendors will be able to use to further reduce performance degrade introduced by Virtual Machine Monitors (VMMs).
VMware will introduce support for this technology with release of upcoming ESX Server 3.5 (formerly 3.1).