4. 4. UI (4-Tier) folder [UI] Difference between 2-tier and 3-tier<br />The easiest way to explain this is, as you suggest, by an example. So I'll give you an example. Let's suppose I'm going to write a piece of software that students at a school can use to find out what their current grade is in all their classes. I structure the program so that a database of grades resides on the server, and the application resides on the client (the computer the student is physically interacting with). When the student wants to know his grades, he manipulates my program (by clicking buttons, menu options, etc). The program fires off a query to the database, and the database responds with all the student's grades. Now my application uses all this data to calculate the student's grade, and displays it for him. This is an example of a 2-tier architecture. The two tiers are: 1. Data server: the database serves up data based on SQL queries submitted by the application. 2. Client application: the application on the client computer consumes the data and presents it in a readable format to the student. Now, this architecture is fine, if you've got a school with 50 students. But suppose the school has 10,000 students. Now we've got a problem. Why? Because every time a student queries the client application, the data server has to serve up large queries for the client application to manipulate. This is an enormous drain on network resources. So what do we do? We create a 3-tier architecture by inserting another program at the server level. We call this the server application. Now the client application no longer directly queries the database; it queries the server application, which in turn queries the data server. What is the advantage to this? Well, now when the student wants to know his final grade, the following happens: 1. The student asks the client application. 2. The client application asks the server application. 3. The server application queries the data server. 4. The data server serves up a recordset with all the student's grades. 5. The server application does all the calculations to determine the grade. 6. The server application serves up the final grade to the client application. 7. The client application displays the final grade for the student. It's a much longer process on paper, but in reality it's much faster. Why? Notice step 6. Instead of serving up an entire recordset of grades, which has to be passed over a network, the server application is serving up a single number, which is a tiny amount of network traffic in comparison. There are other advantages to the 3-tier architecture, but that at least gives you a general idea of how it works. Incidentally, this website is a 3-tier application. The client application is your web browser. The server application is the ASP code which queries the database (the third tier) for the question-and-answer you requested.<br />
![Difference b/w Architechtures<br />The term Architecture in IT generally refers to Client Server Architecture. A client is defined as a requester of services and a server is defined as the provider of services. A single machine can be both a client and a server depending on the software configuration. There are different types of Client-Server architecture available. Some of them are 2-tier architecture, 3 tier architecture, 4 tier architecture and n tier architecture.<br />In 2-tier, the application logic is either buried inside the User Interface on the client or within the database on the server (or both). With two tier client/server architectures (see Two Tier Software Architectures), the user system interface is usually located in the user's desktop environment and the database management services are usually in a server that is a more powerful machine that services many clients. Processing management is split between the user system interface environment and the database management server environment. The database management server provides stored procedures and triggers<br />In 3-tier, the application logic (or) process lives in the middle-tier, it is separated from the data and the user interface. 3-tier systems are more scalable, robust and flexible. In addition, they can integrate data from multiple sources. In the three tier architecture, a middle tier was added between the user system interface client environment and the database management server environment. There are a variety of ways of implementing this middle tier, such as transaction processing monitors, message servers, or application servers. The middle tier can perform queuing, application execution, and database staging. For example, if the middle tier provides queuing, the client can deliver its request to the middle layer and disengage because the middle tier will access the data and return the answer to the client. In addition the middle layer adds scheduling and prioritization for work in progress. The three tier client/server architecture has been shown to improve performance for groups with a large number of users (in the thousands) and improves flexibility when compared to the two tier approach. Flexibility in partitioning can be a simple as quot;
dragging and droppingquot;
application code modules onto different computers in some three tier architectures. A limitation with three tier architectures is that the development environment is reportedly more difficult to use than the visually-oriented development of two tier applications. The most basic type of three tier architecture has a middle layer consisting of Transaction Processing (TP) monitor technology. The TP monitor technology is a type of message queuing, transaction scheduling, and prioritization service where the client connects to the TP monitor (middle tier) instead of the database server. The transaction is accepted by the monitor, which queues it and then takes responsibility for managing it to completion, thus freeing up the client.<br />In a 4-tier architecture, all of the data storage and retrieval processes are logically and usually physically located on a single tier. A 4-tier architecture allows an unlimited number of programs to run simultaneously, send information to one another, use different protocols to communicate, and interact concurrently. This allows for a much more powerful application, providing many different services to many different clients. In this application we will have following 4-Tiers<br />,[object Object]](https://image.slidesharecdn.com/differencesbetweenarchitectures-100224011432-phpapp02/85/Differences-Between-Architectures-1-320.jpg)
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