PCWorld reports that some users are getting back big chunks of disk space after installing Vista SP2. They think that it's because the SP2 install routine automatially removes older system files and restore points via the "compcln.exe" tool but have not received an official explanation from Microsoft yet.

In comments posted in our forums, several readers reported large increases in free hard disk space after installing Vista SP2. Mind you, I'm not talking about a gigabyte here or there; one reader claimed that installing Vista SP2 freed up a massive 40 GB chunk of disk space. Another reader said, "Wow! I didn't notice that til now. I went from about 88GB free to 122GB free. That's a significant change 'under the hood,' isn't it?" And yet another reader gained back 130 GB of hard disk space. Wow.

At least a couple users told me that their free space grew significantly after installing SP2, without them doing anything else. Vista SP2 includes a command-line cleanup tool (compcln.exe) you can run to remove older system files and restore points, thus freeing up hard disk space.

My assumption is that the Vista SP2 installer automatically runs compcln.exe, but we have yet to receive an official explanation from Microsoft. Once we do, though, I'll pass it along. Obviously your milage may vary depending on your system, but I think it's safe to say that most everyone will welcome more free disk space.