explanation about buffers and memory usage ... ?

hi,
just a simple question:
there are at least 4 types of buffers:
shared_buffers
sort_mem
effective_cache_size
geqo_pool_size

can you please tell me when all of this memory is used. what for, and
what's also important.
assuming that i have 16 backends spawned how much memory will it take?
shared_buffers are shared. but what about others? per backend?

depesz

--
hubert depesz lubaczewski                          http://www.depesz.pl/
------------------------------------------------------------------------
... vows are spoken to be broken ...                 [enjoy the silence]
... words are meaningless and forgettable ...             [depeche mode]