SQL Server can be connected to via a number of different protocols, depending on what you've installed, and controlled by the client network utility. The values are stored in the registry in order, and when you specify a connection the topmost protocol is the default connection method.
However, you can specifiy the protocol to use used by prepending it's name in the connection string. This helps guard against connecting via unintended protocols, and also gives a small performance boost by saving a registry lookup e.g tcp:localhost\devsql . You can also save having an initial request to the sql instance monitor port (1434), by specifying the port in the connection e.g tcp:localhost\devsql,1433