Appendix: Virtual Server 2005 R2 SP1

Virtual Server is a Microsoft product for hardware virtualization that predates Hyper-V. Virtual Server will probably continue to be used by customers for some time, in part because it is Microsoft’s only virtualization product for 32-bit systems.

Microsoft’s Virtual Machine Monitor

Virtual Server is a free virtual machine (VM) monitor and provides hardware virtualization for servers. With a VM monitor, only the host OS (the first OS installed on the computer) communicates directly with the hardware. All the other OSs (called guest OSs) and applications installed on these guest OSs run in VMs, which emulate generic resources, including the CPU, memory, disk controller, graphics adapter, and network adapter. Like other hardware virtualization technologies, a VM monitor decouples the guest OSs and the applications running on them from dependencies on specific hardware, enabling multiple VMs to share the same server and to move among servers.

Compared with the Hyper-V hypervisor, Virtual Server has some advantages: It runs more host OSs than Hyper-V, it can be added to existing servers without an OS reinstall, and it supports servers with 32-bit processors. Consequently, it might interest users who want short-term access to a different OS (for application testing, for instance), or if there is a requirement to run a small number of applications on a different OS.