When we describe a typical operating system kernel on a typical machine (be it physical or virtual), we are normally talking about a distinct piece of software which runs in a separate processor mode (kernel mode) and address space from the rest of the software running on that machine. This operating system kernel generally provides critical low-level functions which are leveraged by the other software installed on the box. The kernel is generally a generic piece of code which is trivially tailored (if at all) to the application software stack it is supporting on the machine. This generic kernel normally provides a wide range of rich functions, many of which may be unneeded by the particular applications it is being asked to support.
In fact, if you look at the total software stack on most machines today, it is often difficult to figure out just what application will be run on that machine. You are likely to find a wide swath of hundreds, if not thousands, of low-level utilities, plus multiple databases, a web server or two, and a number of specialized application programs. The machine may actually be charged with running a single applica- tion, or it may be intended to run dozens simultaneously. Careful analysis of the startup scripts will yield hints as to the final solution set which will be run on the machine, but it is far from certain, as a suitably privileged user may elect to invoke any of a number of applications present on the box.
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