How would this happen???
Windows Disk Management reports this drive (and no other drive that I've tried) as being twice as large as it is. Other utilities report it correctly. Disk Management shows the drive as having two unknown partitions (the drive is the "QuickView" version, from a video recorder) in the actual existing space and the "imaginary" area is unallocated.
(In case you're wondering, this drive has 106 reallocated sectors. It seems stable, but just in case it deteriorates later on, I imaged its contents. However, it's a bit bigger than most "80GB" drives, so I can't image onto another one of those from a different manufacturer...)