The document compares the performance of different virtual machine implementations including VMWare Workstation 5.0, User Mode Linux, Bochs, QEMU, and Xen. It finds that VMWare has the best performance due to using virtualization and modifications to the host operating system, while Bochs is the slowest due to using full emulation. QEMU performs well using dynamic translation but could see further improvements from modifying the host OS like VMWare. The document concludes VMWare has the best performance overall if cost is not an issue, while QEMU is a good open-source alternative, and that virtualizing I/O devices and modifying the host OS can help design higher performing VMs.