Citrix and Microsoft are poised to take advantage of increasingly powerful hardware for their server-based computing architectures.
As a result, many organisations could be attracted to server-based computing, also known as thin client, as a way of cutting IT costs, consolidating their servers and having a more secure and controlled PC environment.
Server-based computing environments virtualise multiple application instances on a single server operating system, and allow users to access those applications remotely.
Forrester Research senior analyst David Friedlander said virtualisation, the banner that Citrix Presentation Server and Microsoft Terminal Server come under, can improve server capacity utilisation.
"Organisations have enormous amounts of server hardware capacity that sits idle. For example, capacity utilisation generally hovers between 8% and 15% on Windows/Intel servers and 25% and 35% on Unix and Linux servers," he said.
"Firms use virtualisation technology to collapse multiple, overlapping operating system and application instances running on multiple, distributed servers onto fewer, larger systems."
Citrix and Microsoft have the two most popular platforms for server-based computing, which enable virtualised desktops to run over a network from centralised servers.
Citrix Access Suite (formerly Metaframe) users require Microsoft Windows Server 2003 Terminal Server to run the Citrix Presentation Server software, which is part of the Access Suite. The two suppliers' products go hand in hand.
Users will therefore be required to implement both the forthcoming Windows Longhorn Server version of Terminal Server (about which there are few details available) and a future version of Citrix Presentation Server.
In addition, they will need up-to-date hardware. Users will require servers with 64-bit multicore processors, more addressable memory, and larger and faster hard drives, according to analysts.
Microsoft's Terminal Server test team carried out tests of Windows Server 2003 Enterprise x64 Edition and Windows Server 2003 Enterprise Edition SP1. These found that the software was able to scale to support many more users, if the hardware configuration was right, said Costin Hagiu, a member of the testing team.
The first hardware element that will boost the Terminal Services environment is 64-bit processing.
"On a 32-bit system there is an effective limit of 300 user sessions for typical knowledge worker scenarios. On a 64-bit system, the theoretical user session limit is much higher," said Hagiu.
Multicore processors further boost the number of users that a single server can support. "Benchmark results were able to support as many as 600 users on a single server. This is well beyond the 32-bit architectural limitations," said Hagiu.
Hagiu recommended users plan for adequate addressable memory support, increasing the memory by between 50% and 100% compared with 32-bit systems.
In addition, configurations with a large number of users typically require more robust storage support, that can handle a high level of disc I/O activity from both the operating system and from applications.
Higher performance storage will be able to support page file and user data. "Adequate storage support should include a battery-backed caching controller and an additional hard disc spindle for every 10 users, assuming a typical knowledge worker-level activity of a full desktop, full Microsoft Office suite, and one to three custom applications," said Hagiu.
Simon Frost, product architect at Citrix, said that all the recent advances in server hardware have been good for Citrix Presentation Server, and particularly chip enhancements such as hyperthreading and multicore, which mean multiple applications run faster on a single server.
But he added, "The real boon is in getting more users on a server, and this has been down to the introduction of the x64 server."
This is mainly accomplished by the fact that x64 servers use more addressable memory, aiding multiple kernel requests. "Before, the limit was dual CPUs. The downside of x64 is things such as driver availability, but that is going to improve over time," he said.
As for Citrix's plans for developing the Presentation Server software, "We will always build on the Terminal Services platform, as it is a stronger platform," said Frost.
Moving forward, Citrix is working on Project Constellation to integrate with Windows Longhorn Terminal Services. The latter will have seamless windows, published applications, a web interface, and a Secure Sockets Layer gateway.
But Constellation promises to add to this several new technologies: intelligent and automatic load balancing, server farm health monitoring, automatic and predictive provisioning of resources, and end-user experience monitoring.
Also under development is policy-based session recording, allowing IT managers to record sessions for security and compliance. Constellation will also feature graphics acceleration using 3D computer-aided design, geographic information systems and medical imaging.
With all this in mind, it appears that Citrix and Microsoft are working hard to ensure that server-based computing continues to offer companies a strong alternative to traditional client/server computing.
Alternatives to server-based computing
Server-based computing environments such as Citrix Access Presentation Server and Microsoft Terminal Server are just one way of virtualising desktop PCs, said David Friedlander, senior analyst at Forrester Research.
Other methods include application sandboxing, where one or more applications run in an isolated virtual environment on the PC.
Another alternative is where a desktop virtual machine creates a virtual operating system on a host system so that no software executes on any local hardware.
Blade PCs from ClearCube and Hewlett-Packard are another option. A blade PC runs the entire desktop instance, both hardware and software, on a blade in a datacentre, providing users with remote access to the desktop environment over the network, said Friedlander.
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