Fixed server roles are scoped at the server level, which means that the permissions for these roles are oriented toward server-level securables. These roles contain a variety of fixed permissions geared toward common administrative tasks. Logins (not users) are assigned to these roles.
The same fixed server roles that were available since SQL Server 2008 are still available in SQL Server 2012. The only relatively new role is
public, which was added in SQL Server 2008. Server principals, by default, are granted the permissions that have been granted to the
public role. There are a limited number of permissions that are initially granted to the
public role, but you can change the permissions if you like. A complete list of all ...