Xen 3.0Paravirtualization is State of the Art Virtualization
XenSource was founded by the creators of paravirtualization, the acknowledged state of the art virtualization technology that allows hosted virtual servers to collaborate with the Xen hypervisor to achieve the best performance for enterprise applications, with a smaller code base, greater security and up to 10 times less overhead than alternative virtualization approaches. Other vendors are now rushing to implement paravirtualization but are years behind XenSource. Comparison of Xen Paravirtualization implementation to other approaches to Paravirtualization

Paravirtualization: A New Approach to Virtualization
Pioneered by XenSource, paravirtualization delivers a factor of 10 performance advantage to virtualized servers. With this technology the virtual servers and hypervisor co-operate to achieve very high performance for I/O and for CPU and memory virtualization. In essence, Xen appears to the virtualized server as an idealized hardware abstraction layer that offers superb performance.

Leverages Hardware Virtualization
In addition, Xen uniquely takes advantage of hardware virtualization support from Intel® VT-x enabled processors (and AMD® Pacifica enabled processors in the future) to enable virtualized guests to run natively on the hardware while still achieving very high performance I/O. With alternative approaches, the hypervisor must binary patch running guests to prevent them from interacting with the hardware, resulting in high performance overhead and stability and security risks. Moreover, this approach results in significant I/O performance impact.

Paravirtualization Provides Superior Performance
Paravirtualization requires a tiny hypervisor code base (Xen is under 50 KLOC) that results in extremely low performance overhead, typically in the range of 0.1% to 3.5% for industry standard performance benchmarks. It also leverages all of the native Linux device drivers and therefore supports an extremely diverse set of drivers. Xen’s paravirtualized drivers run outside the core hypervisor, where they implement policy for resource sharing between multiple guests, providing fine-grained partitioning of I/O between multiple virtual servers. Another benefit of this approach is that drivers run at a lower protection level than Xen, making the hypervisor impervious to driver failure.