1. InProc:- In this mode Session state is stored in the memory space of the Aspnet_wp.exe process.This is the default setting.If the IIS reboots or web application restarts then session state is lost.
2. StateServer:-In this mode Session state is serialized and stored in a separate process (Aspnet_state.exe); therefore, the state can be stored on a separate computer(a state server).
3. SQL SERVER:- In this mode Session state is serialized and stored in a SQL Server database.