Multiprocessing

The one main requirement is the obvious one. You must be able
to run multiple (more that TWO) independent processes concurrently.

How you command a process to start is up to you. You might decide
that whenever your shell is to run a .exe program, it creates a    
new process to support it, and the process is terminated when the
program exits. Or you might decide to provide a command for starting
a new process, and have that process be just like the original,
running the shell itself and obeying whatever commands it is given.

You must have a separate page directory (and process control block)
for each process, and a command that lists all current processes
and their status.

There must be something equivalent to a queue of processes that
are ready to run, so that some kind of fairness in sharing CPU
time is enforced.

Pages allocated to processes must be recycled and returned to the
free list when a process ends.

****
    Because I only recently fixed a problem that was troubling at
least (and probably at most, but I'll pretend otherwise) two of
you, I am delaying the other obvious requirement for this assignment.
It hasn't gone away, the requirement has just been postponed. And
this is it: Your OS must provide "pre-emptive" time-sharing. That
is, a timer interrupt is used to enforce fully fair sharing of the
CPU. Each runnable process gets a fraction of a second to do its
work before it is suspended to allow another process to run. And
of course, a process must have a way to voluntarily give up its
turn on the CPU so you can properly demonstrate concurrent execution.