Summary: Depending on how you look at your disk, the amount of space used can appear quite different. We'll look at some of the possible reasons.
In explorer, under the properties of the "C" drive, the space USED is 70 gb. All folders are shown, and by selecting all the files and folders on the drive contents and properties, I get 31gb used. I can not find the other files anyway.
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It's worse than you think. Just with a little poking around I was able to generate several different numbers for the "spaced used" on my hard drive.
I'll admit, it's frustrating. Fortunately it's not something we need look at very often, but you'd think the line between what's used and what's not used would be clear. Actually it is, but there are different ways of looking at "what's used" that don't tell the whole story.
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First let's look at the two examples mentioned in the question. Here's Windows Explorer's view on my C: drive, by right-clicking on the drive and clicking on Properties:
As you can see, Explorer reports that about 47.8 gigabytes are in use, and that 24.6 gigabytes is available as free space. If you're just wondering about the free space on the drive, or how much of the drive is in use, these are actually the numbers I'd use - they take pretty much everything into account.
Now, back in Windows Explorer's view of my C: drive:
Click on any file at the root of C:, and type CTRL+A to select All files. Now, right click on any of the files selected and click on Properties:
![Properties of All Files selected in C:\](http://images.ask-leo.com/allfilesproperties.png "Properties of All Files selected in C:\")
You can see that Windows reports the size of all files in C:\. It reports both size, and something called "size on disk". And neither are the close to the 47.8 gig reported to be in use earlier.
Let's clear up "size on disk" first. Windows allocates space for files in "clusters" or "allocation units". The size of a cluster varies, but ranges from 512 bytes to 32K or more. On my C: drive the allocation unit is 4096 bytes. What this means is that Windows will allocate 4096 bytes for any file or portion of a file that is from 1 to 4096 bytes in length. A 1 byte file? That takes up 4096 bytes "on disk". 100 byte file? Still takes up 4096 bytes on disk. A 4097 byte file? That takes up 8192 bytes - one complete 4096 byte cluster, plus another 4096 byte cluster to hold the extra byte.
So in determining how much disk space is used by the files, we need to pay attention to the larger "Size on disk" number.
But that number is still very different than the 47.8 gig.
There are a number of issues that contribute to the difference:
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Hidden and System Files - The Windows Explorer display above was using the default settings which do not display files marked as "hidden" or "system", and as a result they are not included in the calculation. Changing that setting increases the "Size on disk" by approximately 7 gigabytes as all the hidden files on my machine were included in the calculation. Most notably that included the system swap file and hibernation file, both of which are large, and marked as hidden.
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Directories - directories, or the lists and indexes of the files on your machine, are not files themselves, but they do take up space.
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The File Allocation Table or Master File Table - The FAT itself, of FAT file system fame, is actually pretty small. The MFT however, used in NTFS file systems, is also stored on disk but not visible as a file. It defines where the used and free space on a disk actually is. Depending on the size of your disk, your files, and the size of the allocation unit, the MFT can be quite large.
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The Log File - it's a file, but again, you won't see it. This is internal NTFS data.
There's probably much more that I'm not aware of that enters into the picture as well. I know in researching this issue there was no way I could actually get all the numbers to add up. Possible additional culprits further confusing the situation include compressed files (which appear bigger than they really are on disk), junctions and shortcuts which may or may not be counted as files, utilities which may or may not include the recycle bin as part of the "spaced used" since the contents have technically been deleted, and Windows Vista's ability to keep additional versions of files automatically (though where they're kept and how they're managed, I'm currently not sure).
So yes, it is confusing.
But as I said earlier, I would rely on the drive properties to tell you about the actual used/unused state of your drive.
Article C3122 - August 19, 2007
Is there anyway to make System Restore use less space if we would like to have the benefit of a restore, but not use up all our space? I just saved half my hard drive by taking System Restore off.
Thanks for that, by the way.
23-Jan-2009
in my computer the c drive size become less every day about 1 mb decrease in size of my 9.31gb hard disk, so what is the solution?
Posted by: khan at March 21, 2009 8:07 AMin explorer go to tools, folder options, view. then, make sure to mark "display system folders". you will see a "recycler" folder directly under C-drive. a lot of deleted items are stored there for some reason. so you have to extra delete your files.
Posted by: eindig at May 1, 2009 5:09 AMMicrosoft vista has a automatic back up & restore. It creates a back up point every day or every time you install new software, drivers, or updates. This back up & restore feature is only allowed to use 15% of hard drive space & automatically deletes old back up restore points once it has used up the 15% of space. Now on a 1 terabit drive that's huge. Your hard drive may only have 65 gigs used but with back & restore on it will show an additional 150 gigs used because back up & restore in on.
To turn off, right click "computer" than left click "properties". Now left click "system protection", from that page you will see available hard drive(s) or partitions. Remove the check mark next to the hard drive(s) or partitions you don't want automatic back up & restore on, then click apply. If you want it on, just put a check mark next to the hard drive & click apply. Now if you turn off this back up & restore it will immediately delete all back up points & you will see 15% of your hard drive now available again. A better way to run this back up & restore program is you can manually create them yourself when you want to not lose back up points. It's a great program but it will eat up 15% of you hard drive space, but you will have back up points. One other way which I do is to have a back up hard drive that I manually back up all my info, and store in a safe place. With Vista Ultimate only(not home or other editions & sure about windows 7) you can back up entire system. There are other way also to save back ups, like run two hard drive in raid 0 or raid 1, either raid 0 or 1 I forget now will actually mirror everything from one hard drive to your other hard drive at all times. But will slow down you system, just like running the back up & restore program vista has. My system: 2 terabyte WD hard drive 64 mega of cache (with 3 partitions), ASUS P6T6 mother board, intel i7 core 965 (3.2ghz), Microsoft Vista Ultimate with service pack 2 update, 2 evga gtx 260 superclocked in SLI, toughpower 1000 watt power supply.
02-Jan-2010
Posted by: tigasport at January 1, 2010 6:08 PM
Is it normal for all of my drives other than my "C" drive to show completely full and no available space? And if not how can I clean them up?
Posted by: Bob Bennett at January 24, 2010 12:10 PM