Epson EQUITY 3865X/20 PLUS - Manual (Page 77)

A disk is further divided by sectors, which are similar in shape to
pie slices. The figure below provides a simple representation of
tracks and sectors.
Double-sided, double-density diskettes have either 40 or 80
tracks on each side, and double-sided, high-density diskettes
have 80 tracks on each side. Diskettes can have 8,9,15, or 18
sectors per track.
A hard disk consists of two or more platters stacked on top of
one another and thus has four or more sides. In addition, a hard
disk has many more tracks per side than a diskette, but the
number of tracks depends on the capacity of the hard disk. The
number of sectors depends on the type of hard disk.
Using Your Computer 3-11