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As noted earlier, thin clients are easily capable of handling terminal emulation-to-host computer systems--an important legacy function for mid-to-large-sized organizations. Many thin clients have terminal-emulation software resident in ROM that operates in much the same way as traditional terminals. Others require the download of an application from a server. Still others require the emulation software to be run on the server and displayed on the thin client.

Because Windows has established itself as a legacy application environment in most organizations, any thin-client vendor who expects to achieve broad market penetration needs to provide a vehicle for supporting Windows applications. In most cases, this function is provided via a ROM-resident remote-display protocol. The two most common are Citrix's ICA (Independent Computing Architecture), available for a wide variety of platforms, and Microsoft's RDP (Remote Display Protocol), which is limited to devices that run some variation of the Windows OS. When used in conjunction with Microsoft's Windows NT TSE or Citrix's WinFrame or MetaFrame, these devices display Windows applications that actually run on an NT server. Although a number of implementation issues are associated with deployment of these systems, they are becoming increasingly popular, primarily because virtually all application management can be centralized and the network bandwidth required to support remote users is fairly modest.

While terminal emulation and, to a lesser extent, Windows applications represent legacy environments, modern client/server applications often depend on some combination of HTML and Java for presentation of the user interface. Three-tier client/server applications that use a Web browser as a client talking to a middle-tier application server are increasingly appealing because they minimize the need to frequently update client applications. To address this need, thin clients may include built-in Web browsers and Java virtual machines, or they may require using ICA or RDP remote presentation to handle this task.

Types of Network Computers A number of alternative thin-client implementations are competing for your attention in today's market, each with strengths and limitations. Matching the appropriate device to both your application and infrastructure is a significant challenge.

The hottest new entrant into the thin-client market is the Windows-Based Terminal (WBT). Most early WBTs, which were usually called Windows Terminals, ran a ROM-based single-tasking OS such as DOS together with Citrix's ICA protocol. Wyse Technologies was the first vendor to provide these devices and it has maintained a large share of this market. More recently, vendors have begun to turn to Windows CE as an underlying OS. Not only does this provide Wyse with a popular and compact ROM-loadable, multitasking OS, it also provides inherent support for Microsoft's RDP protocol. Citrix's ICA is also available for CE. Other significant players in the Windows Terminal market include Boundless Technologies, NCD and NeoWare.

CE-based Windows terminals meet the needs of many organizations but are limited by Microsoft licensing agreements that restrict the applications that can run locally to RDP, ICA and terminal-emulation software, all running over a TCP/IP transport protocol. It is not possible for vendors to support a local Web browser or a Java virtual machine. Depending on your application requirements, this may be limiting. An alternative thin client available from many vendors, including IBM, NCD and NeoWare, provides greater functionality than Windows terminals, albeit with the expense of some additional complexity. Built around a multitasking OS, these devices support a Citrix ICA client, X-Windows, a local Web browser and a local Java Virtual Machine. Conspicuously absent is support for Microsoft's RDP. That means you'll need to purchase Citrix's MetaFrame if you want to connect these devices to Windows NT TSE. And because you are supporting more local processing, you should expect some additional management complexity. Some vendors are beginning to develop products that fit into this category using a slimmed-down version of the Linux OS. Given the stability and increasing popularity of that platform, we expect to see some significant interest in these products in the months to come.

Last but not least is the Sun Javastation--the purest play in the thin-client market. This device comes closest to what early advocates of network computers envisioned as a better way of providing manageable desktop computing. In the Javastation environment, all application processing is based on Java applets that are downloaded from servers. Such an approach minimizes the level of desktop configuration management but it limits the application environment somewhat. However, because Citrix supports a Java-based ICA client, you still can have compatibility with Windows applications. While the Javastation can be regarded as a revolutionary product, it has not taken the market by storm. It was overhyped and failed to deliver adequate performance in its initial configuration. Now that performance has been enhanced a bit, the price has been reduced and a few more Java applications are available, the product may yet make a significant dent in the market.

These thin-client technologies can reduce your long-term cost of ownership as it relates to desktop computing, but don't expect to reap the benefits without considerable effort. You still will need to juggle many implementation and management issues, and the level of overall industry expertise is somewhat lacking. A number of system integrators and VARs are specializing in this area, so if you are in a hurry to get something into production, you should definitely look for help. If you are thinking more strategically, it's probably worth the effort to get some of this equipment in and familiarize yourself via experimentation. It's priced at a point where you can probably afford to play around a little. Pay particular attention to application compatibility and performance tuning.

Like any technology that yields long-term benefits, there are some short-term costs associated with thin-client computing. But for many sites, the gain is worth the pain.

Send your comments on this article to Dave Molta at dmolta@nwc.com.