There are two types of client hypervisors. A Type-1 “bare-metal” hypervisor sits directly on top of the client hardware and creates a virtualization layer below the operating system (OS) layer. It then allocates the system’s resources to virtual machines (VMs) running on top of it and supports multiple operating systems that can run side by side in isolation. Citrix Systems Inc.’s XenClient, which became available in October 2010, is an example of this type of client hypervisor.
A Type-2 client hypervisor creates a virtualization layer above the operating system layer and runs as an application that can support multiple virtual operating system instances. VMware’s Local Mode feature, which became available in September 2010, is an example of a Type-2 client hypervisor.
Client hypervisors are useful in that they isolate the operating system from the hardware, making the OS hardware-agnostic. Client hypervisors can also be used to isolate and run different versions of operating systems on the same machine, which isn’t possible otherwise. For example, a user with a Windows 7 machine could run a virtualized version of Windows XP and an older version of Internet Explorer (IE) to access legacy applications that aren’t supported on Windows 7.
In addition, companies using virtual desktop infrastructure (VDI) to deploy desktops can use client hypervisors to support disconnected VDI. One of the problems with desktop virtualization is that users can only access their desktops while connected to a network. With a client hypervisor, their virtual desktop can run on the client device even when the user doesn’t have broadband access.