An Infopath form template is actually a CAB File containing different component files .
Below are the list of files which forms the part of Infopath Template.
1. .xsf file:A manifest file that describes the basic definition of other form files.
2. .xsl file:Defines the transformation for data into different views.
3. .xsd file:defines the data source schema.
4. .dll file:carries the custom logic built into .net or COM.
5. .htm and other resource files:custom html resource files and other resources for the form.
When a form Template is uploaded using Administrative deployment the template is stored in Content Database of the site.
Office Forms Services provide a server-runtime Environment for Infopath Forms Services.While running on the browser ,all rules ,validations,and calculations are executed in the browser using client-side script.
All business logic is executed on the server.So when a browser requests business logic execution,a postback is executed using low cost XMLHTTP.
FormsServer.aspx is an Infopath forms Services page that accesses the form’s data from the content database and renders it to the client.