Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Sometimes I get the feeling that if an app such as μTorrent allocates files on my FAT32-formatted flash drive, but then is killed or crashes (as happens more than a few times a month), that space just disappears from my file system.

Whether or not that is the case, sometimes I do get a chill from wondering if I've lost hundreds of MB in available storage due to carelessness or malfunctions. Checking my disk with WinDirStat just makes it worse, because I see the huge "<Unknown>" item at the disk root staring at me, eating up well over a gigabyte. It might be FS inefficiency (due to 32 or 64kb sector/cluster size and a lot of tiny files) or it might be a glitch...

Is there a tool I can download and run to check my file system and make sure that there aren't any unused allocated blocks on the disk? I want to make sure I'm not losing any disk space to I/O errors, etc.

share|improve this question
What OS are you running? Windows NT, 2000, XP, Vista and 7 all have a Disk Management goodie that shows you allocated disk space. So does Mac OS X (Disk Utility). Each of these OSes also has a facility to check the file system, so I'm not sure what you're asking exactly. – user3463 Feb 3 '11 at 5:44
Windows XP/Vista/7 or Mac OX X 10.4/10.5 depending on where I am – dgw Feb 12 '11 at 0:58
up vote 1 down vote accepted

The FAT controls the allocation of files on a disk. Generally, if the FAT doesn't think a file exists, then for all intents and purposes, it doesn't. Even if there was part of a file written to disk, but this was interrupted and the FAT was not updated, then the OS still thinks that area of the disk is unused and will use it automatically if it needs to.

You can always use chkdsk if you want to make sure your drive is OK.

The item in WinDirStat is usually a result of slack space (non-full clusters) and directories that WinDirStat cannot read, such as System Volume Information.

share|improve this answer

Windows has a utility called chkdsk

Open "My Computer" and right-click on the icon for the drive that is to be checked.

In the context menu that opens, choose "Properties".

Click the "Tools" tab at the top of the Properties window.

In the "Error-checking" section, tick the first box then, click the button "Check now".

**If you check the second box chkdsk will do a surface scan of the disk to check for bad sectors, this will take a long time to run on a disk larger than 40gb.

A box showing the options for running Chkdsk is then available as shown in the figure below.


enter image description here

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.