Microsoft® SQL Server™ runs as a service named MSSQLServer on Microsoft Windows NT®. It does not run as a service on Microsoft Windows® 95/98 because the operating system does not support services. SQL Server can also run as an executable file on Windows NT, although it is usually run as a service.
SQL Server manages all of the files that comprise the databases on the server. It is the component that processes all Transact-SQL statements sent from SQL Server client applications. SQL Server can also execute stored procedures in other remote servers and supports distributed queries that retrieve data from multiple sources, not just SQL Server.
SQL Server allocates computer resources effectively between multiple concurrent users. It also enforces business rules defined in stored procedures and triggers, ensures the consistency of the data, and prevents logical problems such as having two people trying to update the same data at the same time.