There are several different conceptual models of desktop virtualization, which can broadly be divided into two categories based on whether or not the operating system instance is executed locally or remotely. It is important to note that not all forms of desktop virtualization technology involve the use of virtual machines (VMs).
Types of desktop virtualization technologies
Host-based forms of desktop virtualization require that users view and interact with their virtual desktops over a network by using a remote display protocol. Because processing takes place in a data center, client devices can be traditional PCs, but also thin clients, zero clients, smartphones and tablets. Examples of host-based desktop virtualization technology include:
Host-based virtual machines: Each user connects to an individual VM that is hosted in a data center. The user may connect to the same VM every time, allowing for personalization (known as a persistent desktop), or be given a fresh VM at each login (a nonpersistent desktop).
Shared hosted: Users connect to a shared desktop that runs on a server. Microsoft Remote Desktop Services, formerly Terminal Services, takes this client-server approach. Users may also connect to individual applications running on a server; this technology is an example of application virtualization.
Host-based physical machines: The operating system runs directly on another device's physical hardware.
Client virtualization requires processing to occur on local hardware; the use of thin clients, zero clients and mobile devices is not possible. These types of desktop virtualization include:
OS image streaming: The operating system runs on local hardware, but it boots to a remote disk image across the network. This is useful for groups of desktops that use the same disk image. OS image streaming, also known as remote desktop virtualization, requires a constant network connection in order to function.
Client-based virtual machines: A VM runs on a fully functional PC, with a hypervisor in place. Client-based virtual machines can be managed by regularly syncing the disk image with a server, but a constant network connection is not necessary in order for them to function.
Desktop virtualization vs. virtual desktop infrastructure
The terms desktop virtualization and virtual desktop infrastructure (VDI) are often used interchangeably, but they are not the same. While VDI is a type of desktop virtualization, not all desktop virtualization uses VDI.
VDI refers to the use of host-based VMs to deliver virtual desktops, which emerged in 2006 as an alternative to Terminal Services and Citrix's client-server approach to desktop virtualization technology. Other types of desktop virtualization -- including the shared hosted model, host-based physical machines and all methods of client virtualization -- are not examples of VDI.
Top virtual desktop vendors
As the presence of virtual desktop infrastructure grew, VMware -- which came up with the term -- joined Citrix and Microsoft as the leaders in the desktop virtualization market. Other vendors that offer various types of desktop virtualization technology, focusing mostly on client virtualization and remote desktop virtualization, include Parallels International, LogMeIn Inc. and Splashtop Inc.
There are also many third-party vendors whose products and services aim to improve the management, security and usability of virtual desktops. These offerings range from monitoring and application management tools to user environment management and bandwidth optimization software.
Comparing and assessing the major VDI monitoring vendors on the market