How it works
In virtualized desktop environments, the operating system, applications and associated data are abstracted from the user's PC. Broadly speaking, there are two types of desktop virtualization. Local desktop virtualization runs the entire desktop environment in a protected "bubble" on the user's PC. Hosted desktop virtualization stores the users' desktops in the data center, requiring users to access their desktop images through a network connection.
Within these categories are several sub-types.
In the hosted desktop virtualization realm, enterprises can store virtual desktops on a standard server accessed by multiple users simultaneously, or a PC blade architecture in which each blade typically serves just one user at a time. Users can connect to their desktops using thin clients, laptops or regular desktops, but hosted desktops usually preclude any sort of offline access.
Local desktop virtualization is achieved either with a bare-metal, or Type 1, hypervisor, or a Type 2 hypervisor that is installed on top of the PC's operating system. Bare-metal hypervisors are not yet widely available, but vendors say they will provide better security than Type 2 hypervisors, because the bare-metal type runs independently of the client operating system. They also deliver better performance than hosted desktops, because applications run on the local client instead of a remote server. Bare-metal hypervisors are being developed by VMware and Citrix as well as start-ups Neocleus and Virtual Computer. Citrix and VMware plan to release their bare-metal hypervisors in the second half of this year, while Virtual Computer is in beta and Neocleus has released a limited version of its hypervisor.
Local virtualization makes sense for mobile workers, who can be given separate operating systems, one for business use and one for personal use, says Sumit Dhawan, vice president in the desktop delivery group at Citrix. But local virtualization has so far relied on Type 2 hypervisors, and hasn't taken off partly because there is no true independence between virtual machines, he says. When the hypervisor is installed on top of the operating system, all data that goes to the guest operating system must first travel through the primary operating system, and this overhead impacts performance, he says.
Citrix is collaborating with Intel on its bare-metal hypervisor, which Dhawan says will provide great performance for users as well as the convenience of central management for IT administrators. Unlike Citrix XenDesktop, which is hosted in the data center and affords no offline access, the planned bare-metal hypervisor will let users work offline and synchronize changes from a standardized corporate image when they log on.