Types of Client/Server architecture
The PC Terminal - Client/Server type
Despite the appeal of distributed processing, there is still a need for fairly simple structures. As a result, a fast-growing option in Client/Server systems is for the client to be only a sophisticated terminal. Unlike a regular terminal, this version of thin client provides the user interface as well as management of communications. The client appears to be a PC because the part of the OS than handles the presentation of information on the screen executes locally. But it is terminal-like in that the OS boots from the server and application programs run there as well.
The Network Computer (NC) – Client/Server type 2
An alternative thin client approach is to not run a true OS at all, but instead to have a microkernel, written for the specific hardware, that boots locally and then invokes Internet browser-type software from the server. The browser in turn provides the interface from which the user runs application programs on the server. This package, known as a Net PC, will typically have somewhat more in the way of CPU and memory than the Windows terminal, but there is still no local hard disk, or if there is, it is used only for cache.
In the most advanced version of the NC approach, the client and the server will use object-based software, written in Java, that will allow the two share processing tasks dynamically. For example, a database query will trigger a front-end program that resides on the server. The server will download part of the program, in the form of Java applets, for execution on the client. But the server will reserve other parts for itself.
When compared to the full PC client, the NC has the advantage of not wasting money on hard disks or complex client OSs. In many cases, it is actually desirable for the client not to store or manage important information itself. Security is one reason for keeping the client ignorant, but a more important reason is the integrity of distributed systems. In most data systems there is constant updating not only of the data itself, but of the “business logic” that governs their use.
The Network PC (NetPC) – Client/Server type 3
The third approach to the client in Client/Server is a full-powered PC, with normal CPU and memory, but no hard drive. This client needs to have the power to do a lot of work, but should be protected form users messing around with it. They are pretty much like a normal PC except that you can’t open the case. It is so because of security and afraid of viruses.
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