SWI-Prolog provides two different packages for input and output. One confirms to the Edinburgh standard. This package has a notion of `current-input' and `current-output'. The reading and writing predicates implicitely refer to these streams. In the second package, streams are opened explicitely and the resulting handle is used as an argument to the reading and writing predicate to specify the source or destination. Both packages are fully integrated; the user may switch freely between them.