Understanding the Windows NT network I/O stack is important for several reasons. A Windows NT client uses this network I/O stack to access resources controlled by a server and for data communications. In addition, with network-attached storage a situation often arises in which one server accesses resources controlled by another server. A good example is a Windows NT Web server application that, in response to a request from a client, makes a database call to retrieve some data and the database is running on a separate Windows NT SQL server. The Web server application accesses the SQL server using the Windows NT network I/O stack.