3 tier architecture

three layers in 3 tier architecture are

1.Data access layer - All database related classes ,functions,connectionstrings and all database related operations are done in data access layer.

2.Businesslayer - Business layer is an interface between dataaccess layer and your application (for example the data returned by the function in dataaccess layer is returned to your business layer and inturn your business layer returns to your application class)

3.Entityclass - Entity class is  for properties all  values are set and returned in entity class once if you set the value you can use it through out the application.

Advantages of 3 tier architecture

since you have dataaccess layer this is more useful when you are handling large amounts of data.

2 tier architecture

2 tier architecture is simple client/server architecture.

for each request from client it hits the server for response

this type of architecture is not useful when your handling large amount of data because it effects your performance.