In order to make our discussion more specific, let us now limit it to a single type of diskette, the IBM 3740-compatible, soft-sectored, 8-in. diskette.These diskettes contain 77 tracks and either 15 sectors (single density) or 26 sectors (double density), although our examples will permit from 8 to 26 sectors.Normally, only 75 of the tracks are used, thus allowing for two bad tracks.The good tracks are numbered 0 through 74.

The bit pattern of the serially stored information is shown in Fig.9-44. The information is grouped into cells, each of which is divided into four intervals, with the first interval containing a clock pulse.The third interval is for indicating a data bit and will contain a pulse if the data bit is 1.

A representative value for the cell period for a 360-rpm drive is 4 µs.