There are two types of virtualization on the market today. Hardware virtualization, or hypervisor, virtualizes at the hardware level creating a duplicate of all system resources such as operating system, CPU, memory and configuration files. This makes the common point of reference the hardware.
Virtualizing at the host operating system, Parallels Virtuozzo Containers provides a common virtualization layer that allocates system resources across all virtual servers, called containers. The result is a leaner, more efficient virtualization layer with an overhead of only 2%. This translates into higher ratios of virtual servers to physical servers, near-native server performance and unique advantages for management of the virtual environment. Some of these advantages include dynamic reallocation of resources and the ability to create links back to the server host operating system creating lightening fast management operations.
Learn more about OS virtualization.