Is every file an integer amount of bytes?
Yes, every file has an integer amount of bytes. In fact, most file systems deal with blocks or clusters of bytes. If cluster size is 64KB a file may claim to take up 250KB, but it will actually take 4 clusters or 256KB. This reduces the problem of fragmentaton (now fragments can only get so small, and there can only be so many of them) and the problem of addressing (how big do addresses need to be to access any byte in your 500GB drive? Now the addresses can be shorter by 16 bits).