The reason why it is good enough to use a tape is because alignment is not critical. It is enough that sectors that is on top of each other with the same number but at different platter is being read at the same time before the timer runs out. This time is usually +- half a sector. A file is not stored in one platter, but is divided into chunks and divided into all the platters. This is for faster transfer. Each sector on each platter got its own preamble and sync word. Thus, there is no need for bit to bit precision. This wouldn't work either because a slightly different temperature on each platter will move a bit far away, many bits from another bit on another platter, in fact, this is the case even for two bits on opposite side of a platter. It was a time though, with mfm encoding (typically disk less than 100 MB) where there were only one synchronization for the whole drive and where all bits on different platter needed to be exactly where it was with a precision better tha...