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?
Windows was measuring the speed of the drive for ReadyBoost.
You can disable this in the same drive properties.