> this (really nice) PDF isn't complete. It is for the author's definition of "complete", which he gives explicitly early on in the paper. > For me an Operati

> this (really nice) PDF isn't complete. It is for the author's definition of "complete", which he gives explicitly early on in the paper. > For me an Operating System means processes in userland As the reference to the author's late professor in the introduction to the paper will show you, it hasn't always been so. Once upon a time, an "operating system" just meant "the code you have to write before you can do anything at all with this computer". That code could be anything from a special-purpose system for one particular task, to something like MS-DOS, which could run other programs but had no notion of "processes in userland" (because there wasn't any "userland", every byte of code ran on the bare metal), to the kind of multi-tasking system we now generally think of when we think "operating system", like Linux or Windows or Mac OS X.