Quite some time ago I used a friend's computer. I can't remember exactly what I was doing; but as part of whatever it was, I needed to use a USB flash drive. At a point in time soon after connecting the drive to his computer, and while viewing the drive properties through Windows Explorer, I noticed just over thirty megabytes of space became occupied without any user instruction. Within seconds, the drive again showed empty; however, the total amount of space available within that drive was then that same amount of megabytes short. What can be the cause of this strange behavior?

  • It takes Windows a bit of time to calculate how much space is on the drive. I would guess that the 30+MB suddenly becoming occupied is Windows finishing its calculation. It's not uncommon to reserve 32MB of space for a drive's firmware and internal memory.
    – RoraΖ
    Dec 19, 2014 at 13:57

2 Answers 2


This doesn't seem suspicious at all. As raz pointed out, Windows makes rapid estimates of space and then replaces that number with the real number after finishing calculations.

Also, all disks need to reserve space, but again, as raz mentioned, 32Mb is not unreasonable.


Windows was measuring the speed of the drive for ReadyBoost.

You can disable this in the same drive properties.

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