What are the three main purposes of an operating system?

Discuss, with examples, how the problem of maintaining coherence of cached data manifests itself in the following processing environments:

a$.$ Single$-$processor systems

b$.$ Multiprocessor systems

c$.$ Distributed systems

Rank the following storage systems from slowest to fastest:

a$.$ Hard$-$disk drives

b$.$ Registers

c$.$ Optical disk

d$.$ Main memory

e$.$ Nonvolatile memory

f$.$ Magnetic tapes

g$.$ Cache

Describe a mechanism for enforcing memory protection in order to prevent a program from modifying the memory associated with other programs.

How does the distinction between kernel mode and user mode function as a rudimentary form of protection $($security$)?$