For example, if you use a word processor to produce a document,
the word processor is converting your keystrokes into a
file (a stored representation of the
document). In this case the input stream is from the keyboard
and the output is to a file.
When you print the file, you are
converting that file (as an input stream) into a printed
representation---the output stream goes to the printer.
Whenever you type a Unix command, you are creating a
process to carry out the work of that command.
