$[0\mathrm{.}75]$ What are the three main purposes of an operating system?

$[0\mathrm{.}5]$ What is the main difficulty that a programmer must overcome in writing an operating system for a real$-$time environment?

$[0\mathrm{.}75]$ Keeping in mind the various definitions of operating system, consider whether the operating system should include applications such as web browsers and mail programs. Argue both that it should and that it should not, and support your answers.

$[0\mathrm{.}75]$ Give two reasons why caches are useful. What problems do they solve? What problems do they cause? If a cache can be made as large as the device for which it is caching $($for instance, a cache as large as a disk$),$ why not make it that large and eliminate the device?

$[0\mathrm{.}75]$ What is the main advantage of the layered approach to system design? What are the disadvantages of the layered approach?

$[0\mathrm{.}5]$ Why do some systems store the operating system in firmware, while others store it on disk?