There is no neat distinction between operating system software and the software that runs on top of it, ... Thus? Web browsing software can be implemented primarily as an application or middleware that runs on top of an operating system, as Netscape elected to do, or as an integral part of the operating system itself, as Microsoft elected to do, or in a manner that is midway between those two approaches.  -   Jim Allchin     Quotes
There is no neat distinction between operating system software and the software that runs on top of it, ... Thus? Web browsing software can be implemented primarily as an application or middleware that runs on top of an operating system, as Netscape elected to do, or as an integral part of the operating system itself, as Microsoft elected to do, or in a manner that is midway between those two approaches. Jim Allchin