Quoting NetworkWorld

A new version of the open source Xen virtualization stack was released last week, offering up improved support for 64-bit systems, improved virtual server maintenance tools, and a new API for Xen software partners to play with.

While Xen 3.1 has no earth-shattering new features, some incremental improvements will be useful to serious users of mixed Linux/Windows virtualized server environments.

Xen 3.1 now supports both 32-bit and 64-bit paravirtualized machines with its 64-bit hypervisor. This could allow administrators to consolidate legacy 32-bit Linux and Windows servers and applications onto a Xen machine also hosting new 64-bit servers and software. The 64-bit hypervisor also opens up virtualized machines to a whole new level of memory support, up to 64GB of, vs. the 4GB previously supported.

The 64-bit hypervisor could allow users to migrate from 32- to 64-bit machines more gradually, without having to maintain old hardware. Software testers might also find the feature useful for writing code against the two different types of machines.

Live Relocation is another new feature in Xen 3.1. This allows virtualized machines to be moved to another physical, virtualized box without taking the server down. This could be used to gradually move virtual servers off of a piece of hardware in order to service the physical machine, while keeping applications and services available to end-users.

For software developers, Xen 3.1 also includes the XenAPI, which can allow developers of network management tools to tie Xen-based machines into their systems. The API adheres to several virtualization management specifications and standards, including XML-RPC, and the Distributed Management Task Force's (DMTF) standard for virtualization management.

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