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How can There be Used Space on an ‘Empty’ and Freshly Formatted Flash Drive?


When you delete everything from a flash drive and reformat it, you would think it should ‘display’ as completely empty when checked, but that may not always be the case. With that in mind, today’s SuperUser Q&A post has the answer to a confused reader’s question.

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

Photo courtesy of Adikos (Flickr).

The Question

SuperUser reader Andrew wants to know how there can be used space on an empty and freshly formatted flash drive:

I recently purchased a SanDisk Cruzer CZ36 16GB USB 2.0 flash drive with FAT32 as the default formatting. I need to store files that are larger than four GB on this flash drive, so I decided to reformat the flash drive as NTFS. The flash drive also had some SanDisk SecureAccess software preloaded on it that I did not want. On my Windows 7 system, I right-clicked on the flash drive in Windows Explorer and selected Format. I did a full format by deselecting the Quick Format option.

After reformatting the flash drive, Windows tells me that it is not completely empty. If I right-click on the flash drive in Windows Explorer and select Properties, Windows gives me this information:


Why is this the case even though I just formatted the flash drive? Is this to be expected or are there some files still lingering on the flash drive? When I open the flash drive in Windows Explorer, no folders or files appear even though my system’s settings are configured to show hidden items. I find it worrisome that there is a total of 91.7 MB somehow being used on this supposedly “empty” flash drive.

How can there be used space on an empty and freshly formatted flash drive?

The Answer

SuperUser contributor David Schwartz has the answer for us:

This is normal. An “empty” NTFS file system has a number of internal files such as the master file table (“$MFT”), the log file used for file system recovery (“$LogFile”), the volume descriptor file (“$Volume”), and so on.

The largest one is probably the cluster allocation bitmap (“$Bitmap”) that keeps track of the space that is used and the space that is free. This is pre-allocated when the file system is created.

Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

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