I recently purchased a SanDisk Cruzer CZ36 16GB USB 2.0 flash drive. The flash drive was formatted as FAT32 from the package. I will need to store files that are larger than 4GB on this flash drive, so I decided to reformat the flash drive as NTFS. (Also, the drive had some SanDisk SecureAccess software preloaded on it that I don't want.) On Windows 7, I right-clicked the drive and selected Format. I did a full format by unchecking the "Quick format" box.

After the format, however, Windows tells me that the drive is not completely empty. If I right-click on the drive and select Properties, Windows gives me this infomation:

Type:        Removable Disk
File system: NTFS

Used space:     96,169,984 bytes    91.7 MB
Free space: 15,912,419,328 bytes    14.8 GB

Capacity:   16,008,589,312 bytes    14.9 GB

Why is this the case, since I just formatted the drive? Is this to be expected? Or are some files still lingering on the drive?

When I open the drive on Windows Explorer, no folders or files appear, even when I tell Windows to show hidden folders and files. But, still, I find it worrisome that there is 91.7 MB some how being used on this "empty" drive.

  • A full format on flash based memory is not good for the device life time. It doesn't erase every information, because of wearleveling and rescue space.
    – Paebbels
    Nov 5, 2015 at 21:29
  • 2
    @Paebbels: not good for the device life time? AFAIK, NAND flash cells still have a typical write cycle life expectancy in the 100,000 to 1,000,000 orders of magnitude. A single full format writes each bit exactly once. I'll agree that it's a pretty useless thing to do, but I can't see it making a significant difference for the drive's life expectancy.
    – Mels
    Nov 5, 2015 at 22:03
  • Tip: have you also told Windows to show you "protected operating system files"? You still don't get to see everything, but it's a start.
    – Mels
    Nov 5, 2015 at 22:09
  • 1
    @Mels No modern NAND flash cells (< 20 nm) have a write life cycle around 10.000 (as of my knowledge). The wearleveling techniques in modern SSDs and USB flash controllers distribute write access to achive higher life time. Especially TLCs (three level cells) have low values.
    – Paebbels
    Nov 5, 2015 at 22:12
  • 1
    For better performance, it's probably better to do a full format, so the Flash drive knows it has more free space and so in turn has more room for garbage collection and wear leveling. Nov 6, 2015 at 0:23

2 Answers 2


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

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

  • 4
    In addition: This is not restricted to NTFS. Every file system stores itself on the same medium and requires some space. The size depends on the partition size and/or the file count.
    – Paebbels
    Nov 5, 2015 at 21:35
  • Thanks so much. So do you think 91.7 MB of used space is reasonable for a 16 GB flash drive?
    – Andrew
    Nov 5, 2015 at 22:58
  • 1
    0.6% sounds reasonable to me. Nov 5, 2015 at 23:01
  • 1
    @CivMeierFan You can start here or just punch something like "ntfs structure" into your favorite search engine. Nov 6, 2015 at 0:53
  • 1
    @CivMeierFan: The best documentation about NTFS used to be the reverse-engineered specification on the Linux-NTFS Wiki. It was so comprehensive that – according to some curious webserver log entries – it seems it was actually used as training material inside Microsoft. Unfortunately, the Wiki, along with the entire Linux-NTFS project no longer exists. But you can still find some remnants at the Internet Archive's WayBack Machine. Nov 6, 2015 at 8:46

I'm not an expert, but I believe that all USB devices have some code on them that tells the computer what it is. ie. a flash drive, a keyboard, a mouse, etc.

  • 3
    This random computer-related fact doesn't really relate to the question.
    – fixer1234
    Nov 14, 2015 at 4:08

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