One-tier systems run completely from one machine. They tend to be monolithic systems that do not have separate components. If they are monolithic and not built from components, they can only be tested as a single component. Because of the incredible difficulty in testing and maintaining non-modular monolithic system, single-tier systems sometimes have a bad reputation. There are still situations, though, where it makes sense to build this type of application.
An application that runs on a computer and does not need to access data on another machine should use the one-tier model. Examples of such applications are screensaver programs or an appointment scheduler. If you were writing an application that controlled an assembly line that puts caps on bottles and then checks the caps, there would not be enough time to communicate to another computer between each cap. A program that needs response time in milliseconds will probably be one-tier.
Creating one-tier systems is still a large part of what Visual Basic programmers are doing. If you are building these systems, they should be built from components. An excellent example of this is the Microsoft Office suite of products. For the most part, Word, Excel and PowerPoint are one-tier applications.
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