What is 3 tire architecture ?

3-Tier architecture is client server architecture consists of three main layers which are separate from each other.

  

• Presentation Layer: Contains actual display of pages like Html and .aspx etc, where data is presented to user or input is taken from user.   

• Business Access Layer (BAL): Also called as Business logic layer, Contains business logic validations or calculations related with the data. 

• Data Access Layer (DAL): It contains methods that helps BAL to connect to database and perform required action e.g.: insert, update, delete etc.  

check the following urls with example,

http://forums.asp.net/t/1739631.aspx/1

http://www.dotnetpeoples.blogspot.com/2011/04/three-tier-architecture-in-aspnet.html

http://www.dotnetspider.com/projects/811-Tier-Architecture-ASP-NET.aspx

http://www.c-sharpcorner.com/uploadfile/paulabraham/building3tierapppa11282005053625am/building3tierapppa.aspx

diff  between 2 and 3 tier.

http://forums.asp.net/t/1213527.aspx/1 

http://www.codeproject.com/Answers/211574/Difference-Between-1-tier-2-tier-3-tier-Architech-.aspx#answer1

i hope it will help you