As previously mentioned here, here, and here, my new ThinkPad T60 has had a rocky relationship with the new Windows Vista operating system that came pre-installed. (Plot summary: Vista seemed mysteriously to gobble 50 to 60 gigabytes of the hard disk's capacity, leaving barely enough for the computer to function well.)
Thanks to all who wrote in with suggestions. It turns out that the problem was not a big traffic jam in TEMP directories (which I'd cleaned out long ago); nor a CHKDSK-style issue of corrupted or misallocated file space; nor some formatting oversight that had left much of the disk unavailable for storage. It seems not even to be related to space claimed by Vista's built-in indexer. I think I have now fully turned that feature off (which is not easy), but at worst its index files accounted for "only" a gig or two of lost space.
So what was going on?
As many people suspected, the culprit is Vista's enhanced "system restore" or "shadow copy" feature. This is an elaborate counterpart to the "Undo" key in many programs, which lets you restore everything on the computer - programs, data, drivers, configuration - to a backed-up previous state, if you've made some destructive change (or if, say, a virus has gotten in). Great concept! And probably works great on a new desktop with a hard disk three to four times larger than what's on my new notebook. But it is simply too burdensome for a notebook machine, at least mine.
Windows's own help file is, umm, coy about how to rein in this feature. This "KezNews" site gives one approach. Another is to get to the "DiskCleanup wizard" (Control Panel / Administrative Tools / Free Up Disk Space / More Options / System Restore and Shadow Copies) and remove all but the latest backup copy. Theoretically, there is some risk in doing that. But when I tried it just now, the free space on my disk went from 4.5 gigabytes to 14 gigs right away.
There has never been a clearer illustration of one corollary to Moore's Law: that the demands of software will always expand faster than the power of hardware, no matter how fast the new hardware becomes.