Now, Windows Vista is an indisputable resource hog. There is no other way of putting it. Vista will go through CPU cycles with no problems and will swallow system memory like there's no tomorrow. At the same time, the hard drive is also an important part of the hardware puzzle necessary to run Vista smoothly. The Home Basic edition of the operating system requires at least a 20 GB hard drive to install and run, while the Home Premium, Business, Enterprise and Ultimate SKUs cannot do without at least 40 GB. But, all the editions also require a minimum of 15 GB of available space. This because Vista will eat up all you gigabytes.

Go ahead and do a little test for me. Select all the items on the partition where Vista is installed, then right-click one of them and choose properties from the contextual menu that will appear. Now, do the same but for the entire partition. Just take a look at the numbers for disk space. The image included toward the bottom of this article contains the values I got on my machine. According to Windows Explorer, Local Disk (C:) has 13.1 GB of free space of 34.1GB. Sweet! But at the same time, all the items on the partition amount to just Size: 16.0 GB (17,257,535,591 bytes) and Size on disk: 16.2 GB (17,453,596,672 bytes). Hmm... And the properties dialog box reveal that I have 21 GB in used space and 13.1 GB still free for the taking, statistics that coincide with the one provided by Windows Explorer. That's no less than 6 GB of disk space that is occupied by... what?

Don't even try to go hunting for the missing hard disk space. The discrepancy is evident, but you won't be able to correlate it with actual files on the Vista install partition. Fortunately enough, the answer is provided over at Running with Code. "Looks like I've discovered the reason for the space usage - System Restore. Ugh. Hard to believe I've had this installation of Windows active for about, what, not even a week? And System Restore has managed to take up more space than the files I've installed. The good news is, with it set at 15%, I'll probably only get another 7gb taken. Still.... It's just incredible to me that it's filled so fast", reads a fragment of a blog post from Running with Code.

Here is Microsoft's official explanation of Volume Shadow Copy: "Windows Vista includes another useful innovation to help you protect your data: Volume Shadow Copy. Volume Shadow Copy automatically creates point-in-time copies of files as you work, so you can quickly and easily retrieve versions of a document you may have accidentally deleted."