While hardware virtualization is certainly important, virtualizing desktops is also a big deal. Managing desktop systems can be expensive, and so providing virtualized desktops can potentially save lots of money. Given this, Microsoft provides several desktop virtualization technologies, each approaching this problem in a somewhat different way. This section looks at three of them.
Software today typically interacts with people through a screen, keyboard, and mouse. To accomplish this, an application can provide a graphical user interface for a local user. Yet there are plenty of situations where letting the user access a remote application as if it were local is a better approach. Making the application’s user interface available remotely through session virtualization is an effective way to do this.
The idea of session virtualization (formerly known as presentation virtualization) has been around for many years in the form of Windows Terminal Services. Beginning with Windows Server 2008 R2, this useful technology now sits under the umbrella of Remote Desktop Services (RDS). Figure 7 shows how it works.
Figure 7: Illustrating Remote Desktop Services Session Virtualization
Remote Desktop Services Session Virtualization is provided by a specific Windows Server 2008 R2 role: Remote Desktop Session Host. This role works with standard Windows applications—no changes are required. Using this technology, an entire desktop, complete with all application user interfaces, can be presented across a network. Alternatively, as Figure 7 shows, just a single application’s interface can be displayed on a user’s local desktop. This option relies on RemoteApp, a capability that first appeared in Windows Server 2008. With RemoteApp, an application’s user interface appears on the desktop just as if that application were running locally. In fact, an application accessed via RemoteApp appears in the Task Bar like a local application, and it can also be launched like one: from the Start menu, through a shortcut, or in some other way.
Both options—displaying a complete desktop or just a single application—rely on the Remote Desktop Connection, as the figure shows. Running on a client machine, this software communicates with Remote Desktop Services using the Remote Desktop Protocol (RDP), sending only key presses, mouse movements, and screen data. This minimalist approach lets RDP work over low-bandwidth connections such as dial-up lines. RDP also encrypts traffic, allowing more secure access to applications.
The Remote Desktop Connection runs on Windows XP, Windows Vista, and Windows 7. Clients are also available for earlier versions of Windows as well as Pocket PCs and the Apple Macintosh. And for browser access, a client supporting RDP is available as an ActiveX control, allowing Web-based access to applications.
Remote Desktop Services Session Virtualization also provides other support for accessing applications over the Web. Rather than requiring the full Remote Desktop Connection client, for example, the Remote Desktop Web Access capability allows single applications (via RemoteApp) and complete desktops to be accessed from a Web browser. The technology also provides a gateway that encapsulates RDP traffic in HTTPS. This gives users outside an organization’s firewall more secure access to internal applications without using a VPN.
Session Virtualization moves most of the work an application does from a user’s desktop to a shared server. Giving users the responsiveness they expect can require significant processing resources, especially in a large environment. To help make this possible, Remote Desktop Services Session Virtualization allows creating server farms that spread the processing load across multiple machines. Remote Desktop Services can also keep track of where a user is connected, then let him reconnect to that same system if the user disconnects or the connection is unexpectedly lost. While it’s not right for every situation, session virtualization can be the right choice for quite a few scenarios.
© Copyright Microsoft Corporation 2009. All rights reserved.