BitComet only uses more RAM when u enable disk caching which prevents continuous disk read/write activity. It uses up some of ur RAM to store the data and only flushes it to the HDD after u've downloaded say 5 mb of data (you can set this to whatever u want but too large a cache can cause u to lose data, like in case of a power failure). It is advisable that u enable this option to increase ur disk life and prevent a crash (after all it has moving parts which are bound to fail sometime).