I'm sure there's software that takes up some space. Plus all storage devices are labeled based on base 10 calculations, i.e. 1 GB = 1000 MB, 1 MB = 1000 KB, etc. but actually it's 1024. So the actual size is always smaller than marketing labels. That's why you see the notice about size calculation on all hard drives/computers/electronics. So it should be a bit smaller than 1GB.