Xen

Xen is an open-source Type 1 hypervisor that runs directly on hardware, providing strong isolation between virtual machines and forming the foundation of many cloud platforms.

Key Features

• Paravirtualization - Modified guest OS for improved performance
• Hardware Virtual Machine (HVM) - Full virtualization support
• PVH Mode - Combines PV and HVM benefits
• Live Migration - Move running VMs without downtime
• Dom0 - Privileged management domain

Security Architecture

• Minimal TCB - Small trusted computing base
• Disaggregation - Separation of privileged functions
• XSM/FLASK - Mandatory access control
• Stub Domains - Isolated device emulation
• Memory Isolation - Hardware-enforced separation

Use Cases

• Cloud infrastructure (AWS EC2 originally used Xen)
• High-security environments (Qubes OS)
• Server consolidation
• Multi-tenant hosting
• Research and development