The output data files are written in the directory specified by variable outdir, with names specified by variable prefix (a string that is prepended to all file names, whose default value is: prefix='pwscf'). The iotk toolkit is used to write the file in a XML format, whose definition can be found in the Developer Manual. In order to use the data directory on a different machine, you need to convert the binary files to formatted and back, using the bin/iotk script.
The execution stops if you create a file prefix.EXIT either in the working directory (i.e. where the program is executed), or in the outdir directory. Note that with some versions of MPI, the working directory is the directory where the executable is! The advantage of this procedure is that all files are properly closed, whereas just killing the process may leave data and output files in an unusable state.