Increasing hardware virtualization support:
- Historically, virtualization platforms used software to trap and simulate certain instructions, memory management and I/O in the host virtual machines. VMWare was an early leader in this software technology.
- With the first generation of hardware virtualization, the VT-x/AMD-V extensions trapped these instructions in hardware, giving a significant speed improvement. However, virtualized memory management and I/O remained bottlenecks. Xen was an early proponent of paravirtualization, which attacks those bottlenecks by modifying the host operating system at compile time.
- With the second generation of hardware virtualization, the NPT/EPT extensions minimize the memory management bottleneck. As a result, MMU paravirtualization is a legacy approach, leaving just scheduling and I/O to be virtualized in software by a hypervisor. (I/O virtualization requires a good set of device drivers for the underlying hardware, of course: an area in which Linux excels.)

Hypervisor architecture and device drivers:
- Linux KVM is a hypervisor which is built into mainline Linux. It uses the full range of hardware virtualization support, and directly uses the regular Linux scheduler and I/O device drivers.
- Xen runs an external hypervisor for scheduling, and uses a modified Linux kernel in domain 0 to provide device drivers.
- VMWare runs a proprietary external hypervisor, which includes scheduling and device drivers, many of which are adapted from Linux.
- We believe the KVM architecture is superior to both Xen and VMWare, since the mainline Linux scheduler and device drivers are both extremely well designed, widely deployed, professionally maintained and throughly tested, to a level likely well above what a single company can achieve on either their own proprietary codebase or locally maintained fork of Linux.