Tanenbaum:<p>"It is hard to pin down what an operating system is other than saying it is the software that runs in kernel mode--and even that is not always true. Part of the problem is that operating systems perform two essentially unrelated functions: providing application programmers (and application programs, naturally) a clean
abstract set of resources instead of the messy hardware ones and managing these
hardware resources."<p>Yes, it is hard to pin it down. Nor am I sure whether time should be wasted on attempting to pin it down.