Session

InProc means where the session variable will be stored in the procesor .
OutProc are the session modes like Stateserver and Sqlserver
In Stateserver session variables are stored in application domain
In Sqlserver session mode session variable is stored in sql server


The StateServer mode uses a stand-alone Microsoft Windows service that is independent of IIS and can run on a separate server.
In this case the session state is serialized and stored in memory in a separate process that is managed by the aspnet_state.exe file.
This has got some performance drawbacks due to the overhead involved in serialization and de-serialization of objects.
The main primary advantage of storing the Session State in a State Server is that it is not in the same process as the ASP.NET and a crash of ASP.NET
would in no way destroy the session data. Secondly, this mode of Session State storage enables to share the information across a web garden or a web farm.

Rememeber that this mode is slow compared to the InProc mode as it is stored in an external process