ps and wall; How do they work?

[CHOI ANDREW MAN-TAT]

Hello world.  This is my first posting to this newsgroup, please
accept my apology in advance if I have inadvertently violated any
netiquette.

I have the following 2 questions about command 'ps' and 'wall':

1)  How does 'ps' work?  Where does it get the information about all
    the processes running on the system?  I suspect it may have
    something to do with /dev/kmem (Kernel Memory); however, since
    I don't have read/write permission on /dev/kmem, how can
    'ps' acquire the permission to read /dev/kmem?  Is there a
    setuid program exec by 'ps' to get root access?

2)  Even after I do 'mesg n' or 'chmod og-rx /dev/tty?', other
    users can still send me message through command 'wall',
    how come?  Is there anyway to prevent 'wall' from sending the
    message?

Thank you very much for your time and effort in answering these
questions.

Name:  Andrew Choi	Internet Address: achoi at cory.berkeley.edu
Phone: (415)848-5658	Address: 2605 Durant Ave., Berkeley, CA 94704
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