Xen is a free, open source hypervisor first released in December 2005. It is used as the basis for many virtualization implementations, including Citrix's XenServer, and offerings from vendors such as Virtual Iron, Sun, Oracle and Novell among others.
The improvements in the latest version cut across a number of areas, including performance and scalability, efficiency, security, and portability. One long-awaited feature is "memory overcommit," which allows more virtual machines (VMs) to be loaded on a physical server. In addition, VMs can now be moved to servers with different CPUs and still function properly, regardless of the CPU's virtualization support. In terms of "green computing," Xen 3.3 features better power management.
This latest release also unveils the Xen Client Initiative (XCI), an effort to port Xen to laptops, PDAs and other mobile devices. According to a press release announcing Xen 3.3, the XCI has three primary uses initially:
"Using Xen to run 'embedded IT' VMs that allow remote support, security and service of PCs through embedded IT applications without any impact on the user's primary desktop OS; 'instant on' applications that can be immediately available as separate VMs from the user's primary desktop OS; and 'application compatibility' VMs, which allow legacy PC applications to run as VMs, alongside the user's primary desktop OS."
The XCI is a new initiative for Xen.org, the group that manages the Xen project. Xen.org was formerly XenSource, until it was bought by Citrix last September. It exploits a growing field within virtualization, moving beyond server consolidation and into the end user community.
One analyst quoted in the press release said that Xen is on a strong growth curve:
"'The Xen.org community has made security and performance key criteria for the evolution of Xen,' said Zeus Kerravala, SVP, Enterprise Research, Yankee Group. 'This has been a successful strategy, according to recent Yankee Group survey data showing Xen's rapid growth.'"
Xen is not used by VMware and Microsoft, which have their own proprietary hypervisors. Microsoft, however, has made sure its hypervisor, Hyper-V, works very smoothly with Xen-based products. In fact, any VM created on one platform can be seamlessly transferred to the other.
Virtualization is the process of breaking the bond between physical hardware and software. It allows, for example, multiple operating systems, such as Windows Server 2008 and Linux, to be run on the same physical server. Another common use is to run Windows desktop OSes, such as XP or Vista, on a Mac computer.
Xen 3.3 can be downloaded here.
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