In a back-handed reference to market leader VMWare , Citrix says "most virtual desktop infrastructure (VDI) solutions on the market offer only hosted virtual desktops, in which each desktop runs inside a virtual machine in the datacenter." In contrast, Citrix says, version 3 of XenDesktop provides the option to have either hosted desktops, or desktops that get streamed to local devices and execute locally. (For more on the difference between the two, see later in this article.)
Citrix's XenDesktop version 3
(Click to enlarge)
Citrix's XenDesktop architecture stores all virtual desktops on a centrally managed XenServer, represented by the boxes at the right of the above image. The company says its newly released Xenserver 5 offers "bare metal" performance, and can host twice the number of virtual desktops as previous versions.
According to Citrix, users can roam from device to device, authenticating themselves via XenDesktop's SmartCard support, and access their desktops no matter what the capabilities of the "endpoint device" are. If a thin client doesn't have the power to run desktops locally, the desktops run remotely and are sent to the user via "screen scraping."
On the other hand, if the thin client is an x86 device, desktops -- constituting images of both a Windows XP operating system and any applications that have been installed into it -- can be streamed to it and will run locally, "leveraging distributed processing power." Citrix doesn't specify, however, whether the thin clients had to be booted into Windows in the first place, or if Linux-based x86 systems also quality.
Meanwhile, Citrix also touts its HDX (high-definition user experience), a set of technologies that's said to enhanced multimedia performance on thin clients. The HDX allows users to work with USB devices locally, and tap into a thin client's 3D hardware, if present. Via "HDX MediaStream" technology, compressed a/v information -- including DiVX, a variety of MPEG flavors, WMV, WMA, and MP3 -- is sent to a thin client in its native format, and decompressed locally, the company adds.
Background
Desktop virtualization, the most well-known example of which has been VMWare's Virtual Desktop Infrastructure (VDI) , has been steadily gaining traction as a new way of delivering Windows desktops to thin client devices, such as those connected via Microsoft's RDP (remote desktop protocol) or Citrix's ICA (independent computing architecture). Earlier this week, VMware announced an open source (LGPL-licensed) version of its Linux client for use with VDI.
In traditional thin client architecture, available ever since the 1998 release of Windows NT 4.0 Terminal Server, users log on to a host computer whose physical resources -- memory, storage, processor cycles, etc. -- are being shared with others at the operating system level. Examples include Windows Server 2008 or Citrix's XenApp (formerly known as MetaFrame and Presentation Server). With desktop virtualization, on the other hand, the host's resources are divided up by hypervisor software, which creates a virtual machine (VM) for each user. The distinction is not unlike that between a shared web hosting account, and having your own virtual private server (VPS) on the account.
With VM technology, a separate instance of an OS -- usually Windows XP -- exists for each user, whose thin client can be connected to it via RDP or ICA, just as in the past. Virtualization makes a much greater degree of personalization possible, and also allows backing up VMs and moving them from server to server if necessary.
But, says Citrix -- which acquired hypervisor vendor XenSource in 2007 -- VM technology has carried some disadvantages with it. Namely, since each user can have their own operating system and applications, storage requirements can be extensive, and administrators must make the rounds virtually, if not physically, to apply software patches.
Citrix's XenDesktop delivers a "pristine, personalized" operating system image when users log on
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Citrix claims XenDesktop provides the best of both worlds. It employs the XenSource hypervisor technology and uses one easily-managed core operating system image, maintained separately from any end user applications or preferences. When users log on, a virtual machine is dynamically created that includes any previously applied personalizations. As for applications, these are delivered "only as needed and in the most appropriate way as isolated, de-coupled elements on top of the standard core operating system," says Citrix.
The process sounds as though it could take as long as -- if not longer than -- booting a traditional PC. Not so, according to Citrix. Virtual desktops are significantly faster to start up and provide users with an "instant on" experience, Citrix says. They can also be accessed remotely via low-bandwidth or high-latency WAN connections when necessary.
Citrix XenDesktop is claimed compatible with all major thin client products, whether based on Linux, Windows CE, or Windows XP Embedded. It also supports any VM server infrastructure, including Microsoft's forthcoming Hyper-V, and VMware's ESX, says Citrix.
Further information
Most vendors of thin client devices can be expected to support XenDesktop version 5. Wyse was first in, however, announcing "day one" support for the architecture across all its thin client products. In particular, Wyse thin clients will provide SmartCard support, work with the HDX technologies, and deliver USB support, the company says.
Citrix says XenDesktop version 3 will be generally available later this month, with prices starting at $75 per user. More information may be found on the Citrix website, here .
For additional information on XenDesktop version 3, see an article on our sister website eWEEK.com , here .
In other recent Citrix news, the company made an investment in Open Kernel Labs (OK Labs), and has launched a partnership with the mobile virtualization technology firm.
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