Noting with sympathy the plight I described recently -- a 110-gigabyte hard drive drying up like the Aral Sea with each hour's use of Windows Vista -- several readers helpfully wrote to suggest utilities that might solve the problem.

Two in particular: SequoiaView, and TreeSize Professional. Both offer free demos; both are quick and easy to install; both look elegantly designed.


But, no dice.

SequoiaView show me exactly what my existing application, Explorer Plus, had found: an known universe of 32 - 34 gigabyte worth of files. The two largest files, predictably, were a "hibernate" file and a "page" file, each about 2 gigs in size to mirror the available memory in this machine.

TreeSize came up with an additional 10 gigs of file, for a total of 44 gigabytes used. Remember, the disk started with a total of 110 gigs; has a "restore" partition of about 10 gigs -- but right at this moment shows an alarming 4.67 gigs of free space.

That leaves 50 gigabytes of dark matter -- space used up on the disk but not detectable by normal means. I assume it's in the general category of "backup" -- "shadow" files and "version" information, to let me restore the system to a previous configuration. Fine. Problem is, with so little free disk space I can barely use the configuration it's now in. Vista, what's going on?

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.