Magnetic media reading and writing is not an exact process. It isn't a matter of a 1 or a 0, but a wide variance of signal anywhere between a clear 1 or 0. Hard drives, as they get denser, produce hundreds of errors a minute that are corrected by Error Correcting Code, which make informed decisions based on the surrounding bits whether this muddled bit is a 1 or a 0. Same thing happenby crazycarlt - BootMii Beta