03-01-2015, 04:03 PM
No, this has nothing to do with the index pulse.
The bitcell is the duration of a flux pulse. A drive turns a magnetic flux transition (N-S, or S-N) into a square wave that lasts a period of time based on how long the flux transition takes. Typically, these transitions will be 2us, 4us, 6us, 8us, etc. depending on the exact disk format. When a disk ages, the North/South magnetic fields change, so bits will "move" (lengthen or contract). The standard floppy controllers allow a range of 10%-12% of the expected bitcell width for valid data. It is very common that the data can 20% or more depending on how it was stored.
The bitcell is the duration of a flux pulse. A drive turns a magnetic flux transition (N-S, or S-N) into a square wave that lasts a period of time based on how long the flux transition takes. Typically, these transitions will be 2us, 4us, 6us, 8us, etc. depending on the exact disk format. When a disk ages, the North/South magnetic fields change, so bits will "move" (lengthen or contract). The standard floppy controllers allow a range of 10%-12% of the expected bitcell width for valid data. It is very common that the data can 20% or more depending on how it was stored.