IIS has three level of isolation:-
1.LOW (IIS process):- In this main IIS process and ASP.NET application run in same process.
So if any one crashes the other is also affected.
I have hosted yahoo , hotmail .amazon and google on a single PC. So all application and the IIS process runs on the same process.In case any website crashes it affects every one.
2.Medium (Pooled):- In Medium pooled scenario the IIS and web application run in different process. So in this case there are two processes process1 and process2.In process1 the IIS
process is running and in process2 we have all Web application running.
3.High (Isolated):-In high isolated scenario every process is running is there own process.but consumes heavy memory but has highest reliability.