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I often hear this term "3-tier architecture" in reference to Sun Secure Global Desktop Software. What does it mean, exactly?

Thanks,
A reader

Depending on the context, a 3-tier architecture can refer to a number of things. In the case of Sun Secure Global Desktop Software, it refers to how physical machines (or virtual machines) are connected in the software architecture. The Sun Ray architecture is a bit different, so we'll focus on SGD for the moment and address Sun Ray later.

The purpose of SGD is to allow people using all kinds of client devices to access applications executing on other machines.

The emboldened parts of the above statement give us a hint about two of the three tiers in the SGD architecture. The client tier is made up of the device you're actually using. This is your Windows PC, Solaris workstation, Mac OS X machine, etc. The application that you're accessing through SGD is actually running on a machine in a data center and those systems make up the application tier. These can be thought of as "application engines" because their sole role is to execute the applications that people use.

The client tier and the application tier make up the first and the third tiers in the SGD architecture. The middle tier is comprised of one or more machines where the Secure Global Desktop server is installed and is called the access tier:

In a 2-tier architecture you would remove the middle layer and place the logic that used to live there directly on the application engine machines in the application tier. This may seem like it reduces complexity, but in practice it actually places a heavier burden on the application engines and makes installation of new application engine systems more involved. A 3-tier architecture, on the other hand, focuses the role of the application engines by placing a server in the middle to handle the access duties. This server can do lots of very cool things like act as a bastion host to help protect the application engines or improve performance by managing load balancing in unique ways (i.e., geographically). There are many more benefits to this architecture as well which I'll cover in future entries.

 
I downloaded Sun Ray Software 4, but when I looked closely I realized that Sun Ray Server Software is listed as version 3.1. Is there a mistake here?

Thanks,
A reader

No, this is not a mistake. In fact, you'll notice that all of the individual components that make up Sun Ray Software 4 have their own version numbers and none of them are in fact version 4. This was done because significant features were added to the Sun Ray Software package with the addition of the Sun Ray Connector for Windows OS and the Sun Desktop Manager components, but Sun Ray Server Software itself (now just one component of many) was not changed enough to warrant a bump in major version numbers. So as to not confuse existing customers, the individual components kept their own lineage of version numbers and the combined package of software was named version 4.

If it helps, you could look at it this way: