imac idle for a morning and what does it write on disk?

hi
i stated my imac and i left idle for a morning
i haven't stat any program
after i checked the smart and it wrote 3GB
but i have no antivirus nothing that start with my imac , no update , nothing , i left idle
my imac has 32GB of ram


i'm a windows users but now i'm a mac user , and i don't want to go back

i have disabled the sleep image, it seems it does not create a swap file
i have Not started any program , on my login i have no items

i'm not worried ,i'm just curious
what does it...

imac idle for a morning and what does it write on disk?