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Computer networks: What is meant by two tier architecture?

You might have come across the terms “1 tier architecture, 2 tier architecture and 3 tier architecture or application”. But what does these terms actually mean? A lot of people mention these terms, but don’t really know too much about these. In this article, we have discussed in detail about the two tier architecture. However, to understand the 2 tier architecture you first need to understand the concept of client-server model. So let us start on it. A client-server model as the term itself suggests can be thought of as a type of computing model. This computing model works as a distributed application making a data link between the clients and servers.
A server is a typical resource and service provider whereas the client is the one makes a request for a service or a resource to the server. The location of the client and servers or the distance from each other does not matter, since they are said to be present over the same system, once they are connected via the client server model. The communication between the servers and the clients takes place through the computer network established through the internet and on different hardware (but in most cases, this connection can be made securely if required). A computer serving the requests of the clients is called a host or more commonly called a server. These resources are shared among the several clients that may be located worldwide.
In contrast to the server, no data or file is shared by the clients. The communication thus is said to be initiated by the clients. There are several functions that are built on this model of client and server like:
1. Web access
2. Email exchange
3. Data base access etc.
The client server model presides at the heart of this whole computer networking system. Most of the web applications being built today are based on this model.
However, this is not the same as a two-tier architecture. Now let us discuss about the two tier architecture of the applications. The two tier architecture was developed as an attempt to improve the model of the file server application programming. The benefits that the two tier architectures includes scalability, flexibility and usability. As the term “2 tier architecture” itself suggests, it constitutes of two layers or tiers (“tiers” is more appropriate word):
1. Server and
2. Client
The applications built with the 2 tier architecture system usually have a user friendly graphical user interface as compared to the applications employing other types of architectures. But there are also some limitations of this architecture. It does not permit a large number of users to use the application and also the sharing of data can be done only within the homogenous environment and not outside that environment. The two tiers of this architecture have physical separations which are mainly process boundaries, machine boundaries or corporate boundaries. The two tier architecture application is a combination of the client application and server application. Since there is no intermediate application between the two sides, the communication takes place directly. Particular business logic is often incorporated at either side resulting in fat client or fat server accordingly.
The application programming interface or API forms the link between the data base and the client. 2-tier architecture is very cost effective since it requires less deployment cost. If any change is made to the data base of the application, accordingly the modifications should be done in the client side application. If n numbers of clients are connecting to the data base there will be n number of individual data base connections. The two tier architecture is usually used in the development of the localized applications, where the users are all located in a geographic location, and the server processing their requests can be placed in the same location.

Computer Architecture, Fifth Edition Computer Organization and Design Digital Design and Computer Architecture

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