Thank you all (5618, jewelisheaven, Ultima) for telling me that, i knew that in the old days utorrent used a really small footprint. I have disk cache enabled but anyway seems weird to me that it jumps in that hughe blocks and with no torrent added or subtracted that jumped 80M up. @jewelisheaven diskio.sparse_files is default OFF Thank you for that. i really dont mess with that optimisations ... it's now "true" on 1.8.0 so this should be set "false" for vista? Could you please say what kind of mess was that option doing on vista. and is this only if vista is the machine where the files are stored. cause i usually download to network machine. Or it could happen just if host os where utorrent is running is vista. thanks @Ultima I know that pre-allocation of files doesnt have anything with my memory usage. But it's more convenient for me if the files are dynamically allocated.