You need division to go from a file offset in bytes to a sector number, hence the need for power of 2 sizes to make this fast. The kernel assumes in multiple p

You need division to go from a file offset in bytes to a sector number, hence the need for power of 2 sizes to make this fast. The kernel assumes in multiple places sectors are a power for 2 for this reason - it doesn't rely on the compiler to optimize it (which may not even be possible for some of the compilers it works on). If you are talking about using reserved sectors for book keeping at the end of the disk that is possible and commonly done.