Virtual machine (VM) technology has been around for 40 years and has been experiencing a resurgence with commodity machines. VMs have been shown to improve system and network flexibility, availability, and security in a variety of novel ways. This paper introduces Xen, an efficient secure open source VM monitor, to the Linux community. Key features of Xen are:

1. supports different OSes (e.g. Linux 2.4, 2.6, NetBSD, FreeBSD, etc.)
2. provides secure protection between VMs
3. allows flexible partitioning of resources between VMs (CPU, memory, network bandwidth, disk space, and bandwidth)
4. very low overhead, even for demanding server applications
5. support for seamless, low-latency migration of running VMs within a cluster

We discuss the interface that Xen/x86 exports to guest operating systems, and the kernel changes that were required to Linux to port it to Xen. We compare Xen/Linux to User Mode Linux as well as existing commercial VM products.

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