Some CPUs provide for more than two modes of operation what are two possible uses of these multiple modes?

Answer 1

Although most systems only distinguish between user and

kernel modes, some CPUs have supported multiple modes. Multiple

modes could be used to provide a finer-grained security policy. For

example, rather than distinguishing between just user and kernelmode,

you could distinguish between different types of user mode. Perhaps

users belonging to the same group could execute each other's code. The

machine would go into a specified mode when one of these users was

running code. When the machine was in this mode, a member of the

group could run code belonging to anyone else in the group.

Another possibility would be to provide different distinctions within

kernel code. For example, a specific mode could allow USB device drivers

to run. This would mean that USB devices could be serviced without

having to switch to kernel mode, thereby essentially allowing USB device

drivers to run in a quasi-user/kernel mode.