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If I go to Computer (aka "My Computer"), Windows tells me that the G drive has 50.7 GB free of 74.5 GB. If I click into the G drive, highlight all the folders in there, click right and choose properties, Windows tells me the size of everything on the drive is 1.59 GB:

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There are no hidden folders in there (that I know of) and I've defragged the drive, and restarted my computer.

This space discrepancy is apparent on two of my drives. It's not really affecting me right now. But I want to know if there is anything on the drives I don't know about!

Can you explain the numbers or is there a way to "refresh" the stats in Computer?

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Spacing of files on disk has a lot to do with size of files, as well. Some things (programming libraries, for example, which are made up of thousands of potentially very small files) can take dozens of megabytes more on disk than actual size. It's even worse on FAT flash drives, where a 60-80 MB library can fill 120 MB+ of disk. –  ssube Oct 25 '10 at 4:26

4 Answers 4

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The System Restore points take up a massive amount of space in Windows 7, I know this from personal experience...

To to remove old system restore points, click the Start Menu, click Computer, then right-click on the G:\ drive, selecting Properties. Then on the General tab, to the bottom right of the pie graph showing your disk space, click Disk Cleanup. It will run a dialog box, and calculate all the disk space you can free up. In the box that appears after the progress bar, click the second tab, More Options. Then at the bottom, under System Restore and Shadow Copies, click clean up, and it will ask you if you really want to delete all but the most recent restore point. Click Delete and the rest is history!

For disk space visualizers: http://superuser.com/questions/150844/what-app-can-i-use-to-track-disk-space

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Both drives show 0 bytes can be cleaned, and system restore is disabled. –  Matt Oct 24 '10 at 1:56
    
@Matt: interesting...do you have hidden files set to be visible? –  studiohack Oct 24 '10 at 1:58
    
Yes. I just deleted a bunch (>20 gigs) of files. Does that mean anything? –  Matt Oct 24 '10 at 2:07
    
@Matt: try installing and running one of the programs in this question: superuser.com/questions/150844/… - Then you can see at a glance to see what is taking up your disk space, that is if it will show up in the program. Also you'll get a 3rd opinion, by using a software program... –  studiohack Oct 24 '10 at 2:07
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I thought that would be confusing too, so I deleted it. You are too quick though! Anyway, I installed the program, and it found a huge (21.3gig) folder of mine that was marked as a system folder (so it doesn't show in Windows Explorer). I think if I get rid of that, everything should match up. You should put a link to that other question in your answer. Thanks for the help! –  Matt Oct 24 '10 at 2:25

The difference comes from different measures - the two statistics are measuring different things.

When the summary for the G: drive says 50.7GB free of 74.5GB, it's saying that you could store an additional 50.7GB of data on that drive before running out of space.

When you measure the properties of all the files and folders at the root of G:, you're measuring only the amount of data in the primary stream of those files.

What's different? Lots of things.

  • The map of which clusters have been used and which have not is not counted as file content, yet is not free for data storage.

  • Directory entries occupy disk space as well. These entries track which file is in which folder, which clusters are used by which file and so on. In your case you have over 28k files and just over 3.5k directories, so there are a lot of directory entries to be stored - at a minimum each directory takes a whole cluster.

  • NTFS includes some reserved space on the drive which isn't normally available for storing file data.

  • Under NTFS, files can have alternative data streams that store additional information. While usually small, these additional streams can be large.

Also Windows Explorer will often skip folders that are marked as System - especially if they're already marked as Hidden - so the figure shown by the properties dialog can be misleading. The Recycler is one file common skipped(*). Try a program like WinDirStat that shows all file contents to see if you have a large hidden folder.

(*) Files can remain in the recyler if deleted by someone else, so having emptied the recyling bin doesn't mean there are no files sitting there.

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Actually, the reason for the difference in size is because windows doesn't store multiple files in a single cluster, so unless a file consumes a complete cluster or set of clusters, the actual file size is smaller than the amount of disk space reserved for it.

I saw an example once that put it this way: You have 12 ounces of liquid to store, and only had 10 ounce cups. Your 12 ounces of liquid would consume 20 ounces of "storage space", because you can't store another type of liquid in the 8 ounces of space left in the second cup.

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The disk space is most probably being used by System Restore.

Another possibility is a corrupted Recycle Bin, which has files in it, but you cannot see them or easily delete them.

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Is there a Recycle Bin per drive? I thought there was just the one on your main drive. –  Matt Oct 24 '10 at 2:08
    
@Matt: That would mean that when you put a file from drive D: into the Recycle Bin, the file physically moves to C:. It does not do that. The Recycle Bin is actually a virtual folder that contains hidden folders called RECYCLER. There is one RECYCLER folder on each drive/partition, for each user. support.microsoft.com/kb/171694 –  paradroid Oct 24 '10 at 5:55

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