What Is Hardware Virtualization?

Hardware virtualization software makes it possible to allow multiple instances of OSs to exist simultaneously on a computer, with each OS appearing to have sole access to the hardware while in reality it is sharing it with other OSs. Each OS runs in a virtual machine (VM), which emulates a complete computer in software, including the processor, memory, graphics card, network interface, and storage devices (such as disk and CD-ROM drives). A VM is stored as a standard file, on a local computer, the network, or on removable storage, such as a DVD. (In Microsoft’s products, this file is called a Virtual Hard Disk, or VHD file.)

Only the host OS (which is installed on the physical computer and executes when the physical computer starts up) is communicating directly with the hardware. The OS installed in a VM is called a guest OS. To run the VM, special hardware virtualization software (such as Microsoft’s Virtual Server 2005 or VMware’s ESX server) loads and executes the VM file, creating a running computing environment, complete with an OS and any applications that have been installed in the VM. The host OS’s virtualization software creates the VMs and manages and arbitrates each VM’s access to the computer’s physical resources. One physical computer can run multiple VMs simultaneously.