What are two different architecture in software development?
Traditional architecture was monolithic: one big program,
running on a mainframe.
Then, two tier (two layers) architecture came, with PCs talking
to servers, both having some intelligence (applications versus
data).
Then three tier architecture arrived, powered by internet
technology, Java and .Net. Data, applications and presentation are
separated in this architecture. Presentation is almost always in a
browser, the application and the data run on servers, usually in
the corporate data center or somewhere 'on the internet'.