hi, i need some light . sorry if this question is dumb one

im using fx8350 16gb ram, all core are used and not overclocked(standart 3.99ghz) until im feel my room to hot and try to lower the temp. it worst after gaming session, but temp are not the main issue .
the main issue is i just realize i when turn off 4 core,2gb usage on rams idle and max 4~5gb.
but when all 8 core are used, idle mode ram usage is at 4gb all the time and sometime jumps up to 8gb ?

task that main use:
dota,utube,and bluestack(for coc) , if i open all those at once, rams usage sure jump to 7~8gb when all 8 core are used,
but not when im used only 4 core



its not big problem, but its attract my attention to looks for answer, thx for help or even reads.
and 1 more question if there any news for fx series to get mini itx mobo, its time to turn mid tower to miniature one