Desktop virtualization, which is only a step towards enterprise cloud computing, must consider the integration of hypervisors, hardware systems, client devices and operating systems as follows:
Virtualization requires the interposition of a hypervisor, also called the virtual machine monitor (VMM), between hardware (usually a microprocessor) and the operating system. Virtualization then permits multiple operating systems, termed guests, to run concurrently on a host computer. There are two types of hypervisors:
Type 1 (or native, bare metal). It runs directly on the host's hardware. It controls the hardware and monitors guest operating systems. The guest operating system runs above the hypervisor. Type 1 hypervisors include the Microsoft Hyper V; Intel's Intel VT-x; AMD's AMD-V; Citrix XenServer; and VMware ESX.
Type 2 (or hosted). It runs within a conventional operating system. The hypervisor layer is a second software level with the guest operating systems running at the third level above the hardware. Type 2 hypervisors include Sun VirtualBox, VMware Server and Microsoft Virtual PC.
When setting up desktop virtualization, the hardware and software interfaces must recognize which of the multiple hypervisor options it will have to interface with.
There are a total of 2,814 listed versions of systems that desktop virtualization may have to interface with. This includes Bull (51 systems); DELL (124); Fujitsu (78); HP (144); IBM (114); NEC (87); Oracle America, Inc (formerly Sun Microsystems, Inc) (67). If desktop virtualization connects to legacy hardware, it may have to recognize what changes were made in the interfaces.
There are a total of 1,811 listed versions of desktop clients that virtual computers located on servers may have to interface with. This includes DELL (183 systems); HP (208); (IBM (195); Intel (220; and Sun Microsystems Inc (85).
There are a total of 1,210 listed versions of operating systems that the hypervisors may have to interface with. This includes Apple (64); FreeBSD (43); Microsoft (280); Novell (177); Red Hat (334); and Sun Microsystems Inc (37).
Desktop virtualization, especially when it calls for migration from legacy environments, is complex. It may call for the construction of bridges between hardware, clients and operating systems until such time when a consistent architecture, based on open standards, can simplify how an enterprise functions.
Meanwhile, enterprises are saddled with thousands of possible combinations that have been introduced by the diversity in legacy contracts. Whoever supports the estimated ten million clients in the Federal Government should have every incentive to cut back on the complexity that slows down the migration to a more secure and lower cost desktop virtualization environment.
To quote Ray Ozzie: "Complexity kills!"
(1) All tables obtained from http://www.vmware.com/resources/compatibility/search.php?deviceCategory=vdm