Does .NET controls SQL SERVER or is it vice-versa?

SQL Server controls the way .NET application will run. Normally .NET framework controls the way application should run. But in order that we have high stability and good security SQL Server will control the way .NET framework works in SQL Server environment. So lot of things will be controlled through SQL Server example threads, memory allocations, security etc .
SQL Server can control .NET framework by "Host Control" mechanism provided by .NET Framework 2.0. Using the "Host Control" framework external application's can control the way memory management is done, thread allocation's are done and lot more. SQL Server uses this "Host Control" mechanism exposed by .NET 2.0 and controls the framework.