Windows Explorer shows for my USB drive less capacity than it should, i.e. 499MB instead of 512MB, as expected.
This is because hardware manufacturers count 1k = 1000 Bytes and the Windows operating system uses 1k = 1024 Bytes. So this is actually a rounding error and Windows will show less capacity for the USB drive. Another part of the storage space is occupied for the formatting table of the file system and therefore it is not effectively usable.