Understanding top (or ps)

[Eric LeBlanc <inouk_(_at_)_igt_(_dot_)_net>]

Hello,

in man top I have:
SIZE is the total size of the process (text, data, and stack), 
RES is the current amount of resident memory

and in man ps, I have:
vsz        virtual size in Kbytes (alias vsize)
rss        The real memory (resident set) size of the process (in 1024
byte units).

if I type: ps auxv
[skip]
USER       PID %CPU %MEM   VSZ   RSS TT   STAT STARTED       TIME
COMMAND           SL  RE PAGEIN   LIM TSIZ
inouk    19049  0.0  3.8   928  1536 p0  Is    Sun04PM    0:01.26 -tcsh
(tcsh)     127 127      0 34524  276

here, I have:
VSZ  == 928
RESS == 1536

If I read carefully in man ps and top, I mean VSZ containt all data,
text and stack.

But... why RSS is more higher than VSZ ?  RSS is the real memory used by
the process (physic), and, usually, it's contain a certain portion from
VSZ no?

Thanks for your help...

Eric