Explain 2-tier and N-tier architecture?

2-tier Architecture
Typical client/server systems are all 2-tiered in nature where the application resides entirely on the client PC and database resides on a remote server. But 2-tier systems have some disadvantages such as:

* The processing load is given to the PC while more powerful server acts as a traffic controller between the application and the database.

* Maintenance is the greatest problem. Imagine a situation where there is a small modification to be done in the application program. Then in case of a 2-tier architecture system, it is necessary to go to each client machine and make the necessary modifications to the programs loaded on them. That is the reason why the modern web applications are all developed based on 3-tier architecture.

 N-tier Architecture
Although the title of this section is given as N-Tier architecture, here the concentration is on the 3-tier architecture. Basic reason for this is that any web application developed based on N-tier architecture functions just similar to typical 3-tier architecture.

* First-Tier:

* Basically the presentation Layer.

* Represented by the GUI kind of thing.

* Middle-Tier :

* Application Logic

* Third-Tier :

* Data that is needed for the application.
The basic idea behind 3-tier architecture is that to separate application logic from the user interface. This gives the flexibility to the design of the application as well as ease of maintenance. If you compare this with 2-tier architecture, it is very clear that in 3-tier architecture the application logic can be modified without affecting the user interface and the database.