Input (grade 13): Usage with the Linux kernel is by far the most popular distribution vector for GNU software, though the Linux kernel itself is not part of the GNU Project.
Output (grade 12): The central part of the operating system, called the Kernel, is not finished, and lots of people use the Linux kernel with GNU (which is called a GNU\/Linux Operating System). Software that runs on the GNU system often has been made for other computer software systems like Microsoft Windows and Mac OS X.