Growing interest in blade PCs—standardized, rack-mounted computers running Windows XP Professional—has prompted Microsoft to develop a special license for the Remote Desktop technology included with the OS. Like the blade servers frequently used for high-capacity Web sites, and like remote access through Windows Server's Terminal Services feature, remote access to blade PCs offers centralized control of hardware and applications. However, in most cases Terminal Services will be less costly, more manageable, and more flexible.

The Blade PC Architecture

Around in one form or another since about 1997, blade PC hardware is very similar (and can even be identical) to blade servers: single-card computers that fit into slots in a rack-mounted enclosure or "crate." The enclosure provides redundant power supplies, network connectivity, ventilation, and cable management for 20 or more blades.

As servers, such devices are popular for high-volume Web hosting: a single rack about two feet wide and six feet high can hold about eight enclosures, each holding 20 blades, each blade hosting 100 Web sites, for a total of more than 15,000 logical Web servers in a relatively small space.

Blade PCs run a desktop OS instead of a server OS. Promoted primarily by Hewlett-Packard (HP), blade PCs are designed to be accessed remotely by a thin client running Linux, Windows CE, or Windows XP Embedded, such as HP’s T5700, Wyse’s Winterm thin clients, or even handhelds such as Compaq iPAQs. The blade PC runs the application but displays its output on, and accepts input from, the remote device.

Blade PC Scenarios

As with the terminal server approach, the blade PC lets an organization such as a hospital or school benefit from the simplicity of thin clients while having access to all the software that will run on Windows XP.

When the blade PC is running Windows XP Professional, remote users can access the blade PC desktop environment from a conventional PC desktop or a thin client by using Windows XP’s Remote Desktop feature. Unlike Windows Server running application-mode terminal services, Windows XP does not allow simultaneous access from multiple clients, a limitation that can actually be an advantage in some scenarios. For example, an organization might have a CPU-intensive application that, for performance or licensing reasons, is limited to 20 simultaneous users. By loading the application on 20 blade PCs, the organization ensures that those who use it have exclusive use of the host PC’s CPU and that no more than 20 people will be using the application at any given time. Others who try to access the application will receive a message that a PC is unavailable.

In addition, PC applications that will not run on a multiuser server running Terminal Services might be able to run on a dedicated blade PC.

The main disadvantages of blade PCs are their cost. At any given time, each user requires two PCs, the client and the blade. In spite of their small size and the fact that they don’t have power supplies or cases, blade PCs are not necessarily cheap. HP’s blade PCs cost US$820 each, the HP thin clients start at US$349 each, and an HP enclosure for 20 blades costs US$3,500, for an average hardware cost (excluding monitors) of more than US$1,300 per user, with a fully packed enclosure. In addition, organizations may need load-balancing hardware to efficiently allocate blade PCs to users, and a secure space, such as a data center, to maximize the security advantages of blade PCs, such as the ability to keep users away from the physical consoles.

Finally, although blade PC vendors promote the management simplicity of the blade PC architecture, which can reduce "deskside" visits to client PCs, it increases the number of devices that must be managed and patched.

Licensing Blades

Until Microsoft changed some of its licensing rules, blade PCs had the potential to affect Microsoft revenues negatively: organizations could download Microsoft’s free Remote Desktop Connection software for OSs as old as Windows 95 and use blade PCs to run a few Windows XP-specific applications their organization might require without upgrading every desktop OS.

To ensure that this does not happen, Microsoft has tightened the product use rights for Windows XP and now requires clients accessing blades to have another Windows XP license, or to be the primary user of a particular blade. Starting in October they will be modified again to take into account a scenario that is currently not permitted: access to a blade PC by someone who is not the primary user and who may not be using a device licensed for Windows XP. They will use, instead, a special Remote Desktop License (RDL).

Changing Product Use Rights

Before July 2004, the company’s product use rights permitted "any device to use, access, display or run [the Remote Desktop] without acquiring a license for the Software on that device," as long as no more than one person accessed the host PC at one time.

After July 2004, however, that section of the product use rights document was modified to say that the Remote Desktop may only be accessed from other devices "provided you acquire a separate [Windows XP] license for that device." An exception is made for a person who is "the single primary user of the host PC." The new language covers remote access using any software, including third-party remote access software, such as Symantec’s pcAnywhere.

The product use rights that govern a software product are those in effect at the time it is purchased, so blade PCs with Windows XP licenses purchased prior to July 2004 could be used under the old terms, but any blade PCs shipping after that time are subject to the new restrictions. Microsoft has also changed language in OEM and retail versions of Windows XP to reflect the new language.

The Remote Desktop License

Customers who want to access blade PCs and do not have another Windows XP license for the client device accessing the blade, or are not the single primary user of the blade PC, are currently not permitted to use the remote desktop. Microsoft’s solution to that problem is the RDL.

An RDL, which is purely a license and does not include or accompany any software, permits remote access to a PC running Windows XP Professional without requiring the remote device (which could be a cell phone) to be licensed for Windows XP or the user to be the single primary user.

RDLs will be available in both per-device and per-user versions. A device RDL enables a device without an XP license to access Windows XP remotely, no matter which individual is using the device. This would be appropriate for a terminal used by several shifts of workers, for example. A user RDL permits a single user to access Windows XP remotely from any device, and would typically be used by someone accessing a blade PC with both a handheld device and a desktop computer.

An RDL does not give a remote user the right to use any applications that might be installed on a Windows XP host computer; those applications must be licensed separately, on whatever basis the application vendor dictates.

RDLs will be available starting Nov. 2004 through Microsoft volume licensing at an estimated volume price of US$170 per license or lower (depending on the number of licenses purchased and reseller discounts). They will also be available through OEMs of blade PCs: each copy of Windows XP sold with a blade PC will include one RDL. Microsoft’s product use rights will also be modified to take RDLs into account.

Terminal Servers vs. Blade PCs

Organizations considering blade PCs (or some other devices, such as conventional PCs) to host Windows XP sessions for remote access will need to compare them with the alternative of Windows Servers running Terminal Services, a remote desktop service which has been included with Windows Server since Windows 2000.

Terminal Servers have some weaknesses compared to blade PCs, including the following:

Not all Windows applications can be installed or run on a terminal server.

Performance degrades as the number of simultaneous sessions hosted by one server increase.

Terminal Services licensing is more complex, requiring a Windows Server CAL and a Terminal Services CAL, plus licenses for any applications that the user accesses, and a Terminal Services licensing server.

However, terminal servers also offer some advantages over blade PCs, including the following:

Less costly hardware and licensing because one computer can host dozens of remote users. If those remote users are not using Windows XP Professional clients, a Terminal Services CAL costs US$78 or less (about US$90 less than an RDL) in volume purchases.

System management is simpler because a patch applied to a single Terminal Server patches all terminal sessions on that computer; blade PCs must be patched individually, although tools such as Systems Management Server can streamline some patching.

Session state is preserved in the event of client or network failure. For example, if a remote device fails while updating a spreadsheet via Terminal Services, that session is restored in its exact state, with the spreadsheet open in Excel, when the user reconnects to the Terminal Server. Achieving the same result with blade PCs is more complex because the user must reconnect to the same blade, which can be difficult if the blades are allocated to users by a load-balancing system.

Resources

A licensing brief describing licensing in blade PC environments is listed at www.microsoft.com/licensing/resources/volbrief.mspx.

HP’s blade PC architecture, called "consolidated client infrastructure" is described at h71028.www7.hp.com/enterprise/cache/9885-0-0-225-121.aspx.

Microsoft volume licensing information, including the Product User Rights document, can be found at www.microsoft.com/licensing.

Remote Desktop Connection software for older OSs can be downloaded from www.microsoft.com/windowsxp/downloads/tools/rdclientdl.mspx.

For a list of the most recent Directions on Microsoft coverage of licensing topics, see the Recent Changes to Microsoft Licensing page.