Bests & Worsts Reviews from Amazon

I buy a 128GB Flash Drive and when I connect it to my PC it shows me 119GB of free space. Did I miss something? Where are the additional 9GB? I feel a bit cheated...the screenshot shows it. I'm not an IT expert, but if I buy a gallon of milk...it should be a gallon inside, right...this is how I see it here. I bought a 128GB drive, but it's not!