Can't I just run a Terminal Server Session on a PC?

This is a question that we get frequently, and while the short answer is 'Yes', once people understand the differences between running a Terminal Server session on a full PC and running it on a true Thin Client most people choose to use the dedicated Thin Client, especially for industrial applications. A comparison between these two platforms explains why.

Windows 2000 and TSAC

Not long after Microsoft released Windows 2000 Server they released a component that allowed anyone running a Windows based PC to bring up a window on their desktop that could be used to display the interface of an application running back on the server. Known as the Terminal Services Advanced Client (TSAC), this ActiveX plug-in for Internet Explorer allows a user to start a Terminal Services session from within his browser. I believe that a very strong case can be made against using TSAC for anything more than initial testing and occasional use within an office, and the reasons all stem from the fact that a PC is required to host the TSAC session. This negates many of the advantages of running an application on the Microsoft Terminal Server platform.

First of all, someone must keep the operating system on every PC running the TSAC sessions current and loaded with the necessary support applications. A PC left alone and used only to connect back to the server should work the same tomorrow as it does today, but if there is ever a problem (especially with the hard drive) deploying a PC with the same configuration may be difficult. Also, it may not be that easy to keep the same software running on the client PC. The Server will be kept current, and it is often the case that a change in the Server software will require an update of some of the software installed on the clients, most likely an update to Microsoft Internet Explorer. And putting a PC on the factory floor means that you now have disk drives in the manufacturing area, adding a failure prone component to a machine that may need to run 24 hours a day.

A backup of each client PC must also be kept, in case the PC has to be restored. If this is an image backup, it may be difficult to find disk drives of the right size later as technology advances and these PCs are left behind. Remember - the useable lifespan of a PC is less than 4 years.

Theft is another consideration. Both the data (which may be taken via the PCs local disk drives) and the PC itself have to be protected. And local floppy drives also make it much easier for operators with idle time to add unwanted software or viruses.

What happens if the PC looses power suddenly? While the application continues to run back on the server, the PC that was running the TSAC session may not boot up correctly once power is restored. Unexpected power loss may occur due to normal electrical disturbances, but it is more likely that the frustrated user who has a problem with any component required to display the Server session will select the remedy of cycling power on the PC.

A PC with a full Windows Operating system and with a full compliment of disk drives and PC support hardware that runs a Thin Client session is often referred to as a 'fat client' because it is getting away from one of the major advantages of the Thin Client - being able to deliver a standard application on minimal, commodity hardware.

ACP Enabled Thin Clients

This type of dedicated Thin Client has no local applications and no hard drives. It is truly a dumb terminal that connects to the server and displays the output from any application running on the server. The only requirement is that the program run under Windows 2000. Once that condition is met, the operator at the Thin Client sees the display exactly as if he was running the application locally.

Most of the customers that we see would rather have this type of 'dumb terminal' and so they put in a true Thin Client, where there is no chance of the device ending up with an old version of a display program. And with ACP enabled Thin Clients, even the drivers that are used by the Thin Client are loaded each time that the unit is powered on, assuring that the device is always running the latest copy of these as well.

And in terms of reliability inside a factory, true Thin Client hardware is designed to minimize complexity, eliminating components prone to failure (such as disk drives) and scaling back parts (like memory) that are required for a traditional PC. Since the application running within the Explorer window is running entirely on the Server the exact same effect can be achieved by replacing the PC hardware and operating system on the Fat Client with a piece of hardware designed simply to display the session. On top of this cut-down (or "thin") hardware a minimal operating system is loaded, with just enough power to drive the graphics card, some I/O and an Ethernet Port. The Thin Client now has been streamlined to allow it to do just what it was designed to do - separate the application processing layer of a program from the user interface.

A lot of companies are coming out with software designed to work with Thin Clients - just make sure that you have picked the right hardware that will let you take full advantage of the Terminal Server model.