user and kernel space ?

[Mcen navaraj <mcensamuel@yahoo.com>]

hi,

what is the use of two privilege level ?
is there any performance is increase if we implement
some
program in the kernel space ?

in linux please tell me in which space ( user or
kernel ) 
the X11 is implemented ?
why i am asking this question means if sometimes the
system
hangs , only the start menu ( that is k in kde ) is
quickly 
popup's.Another reason for asking this question is my
friend told the desktop in windows95 is implemented in
the
kernel space.

please give me some useful info ( anything related to
the
windows or linux ).

thanks
bye


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