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Client-side rendering in Windows Server 2008 R2's RDS

Client-side rendering is one of Windows Server 2008 R2's Remote Desktop Services most compelling new features.

This is part two of a three-part series on the top features in R2's Remote Desktop Services.

When Microsoft purchased Calista Technologies in early 2008, rumors spread that it was making changes to Remote Desktop Service's core, Remote Desktop Protocol.

Calista delivers technology that virtualize the Graphics Processing Unit (GPU) of a host computer, which dramatically improves the RDP protocol in multimedia rendering, bidirectional audio and data streaming across an RDP connection.

Microsoft's acquisition of the software vendor further enables a separation of graphics processing between the host and the client.

Consider the bandwidth and processing requirements for creating a graphic. Individual graphics instructions transferred from server to client in raw formats require significantly less bandwidth than rendered images. However, at the same time, graphics instructions sent in a raw format require client processing in order to be converted to a real image.

Therefore, although client-side rendering requires more processing power from the client, the benefit is a lighter data stream.

In addition, reducing the level of graphics processing at the server enables it to service more clients at the same level, and multimedia – the long-held bane of Terminal Services -- can be more effectively rendered by the local client than the server.

Calista's integration results in a better and higher-performing RDP, specifically with graphically-intensive applications.

That being said, Microsoft's implementation of Calista technologies remains limited in R2.

In the latest version, client-side rendering supports Remote GDI, the built-in Aero Glass experience, and any Windows Media Player content.

Available in the Beta and RC versions -- but removed prior to release -- was DirectX 10.1/DXGI 1.1 and Direct2D rendering. Microsoft suggested this change had to do with the limited number of applications that can, and currently are, being developed atop the DirectX 10.1/DXGI 1.1 API.

The removal affects the few organizations developing applications based on this bleeding-edge DirectX standard.

Its more-potent impact, however, is the ability to display a more Windows 7-like experience through the RDP connection.

Leveraging the aforementioned client-side rendering capabilities, Windows 7 clients can experience the familiar Aero Glass interface by enabling the Desktop Composition feature in RDS's "Configure Client Experience" node during installation or afterwards through the management console.

Today, this capability is only supported for Windows 7 clients connecting to R2 servers. It is unknown whether this capability will be back-ported to earlier client versions.

Another feature on the client side is the new, multi-monitor support for Windows 7 clients.

Although the previous version introduced the "/span" switch, which enabled a Terminal Services session to span across monitors, it was limited to identical vertical resolutions that could not exceed 4096x2048.

R2's multiple-monitor technology effectively extends a Remote Desktop session across any local client monitors in any configuration.

See how this looks across six separate monitors in a non-rectangular configuration at Microsoft's Remote Desktop Services Team Blog.

This is only number two on our list of the most compelling new features in Windows Server 2008 R2's RDS.

Stay tuned for the number one capability -- which spans multiple technologies for the rich support of applications -- in the conclusion of the series.

Greg Shields
, MCSE, is an independent author and consultant based in Denver with many years of IT architecture and enterprise administration experience. He is an IT trainer and speaker on such IT topics as Microsoft administration, systems management and monitoring, and virtualization. His recent book Windows Server 2008: What's New/What's Changed is available from Sapien Press.

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