Xen Hypervisor Virtualization Platform

Xen is a free and open-source type-1 (bare-metal) hypervisor enabling multiple operating systems to run concurrently on the same physical hardware, providing strong isolation and efficient resource management. Originally developed at the University of Cambridge Computer Laboratory by Ian Pratt and Keir Fraser in 2003, Xen is now developed by the Xen Project under the Linux Foundation. Key features: type-1 architecture running directly on bare metal with no host OS, providing minimal overhead. Domain 0 (Dom0): privileged management domain running a paravirtualized Linux kernel managing hardware drivers and guest lifecycle. Guest domains (DomU): unprivileged VMs running their own OS, isolated from each other. Paravirtualization (PV): modified guest kernels aware of the hypervisor, achieving near-native performance. PVH (PV on Hardware): hybrid mode combining PV efficiency with hardware virtualization extensions (Intel VT-x/AMD-V). HVM: unmodified guest OS via hardware-assisted virtualization. Live migration: running VMs migrated between hosts without downtime via pre-copy memory transfer. Xen on ARM: support for Cortex-A15, A53, A57, A72, A76 with ARM virtualization extensions. Schedulers: credit (default fair-share), credit2, RTDS (real-time deadline). PCI passthrough: direct device assignment via IOMMU. XSM (Xen Security Modules) with FLASK/SELinux for mandatory access control. DISA STIG certified. Qubes OS uses Xen as its core isolation mechanism. Citrix Hypervisor (XenServer) is a commercial product. Used by AWS EC2 and Alibaba Cloud. GPL-2.0.