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Chapter
3
Theory of Operation
Introduction
This chapter describes the flexible disc recording fundamentals, and functional block dia-
gram theory of operation. Refer to Figures 3-1 through 3-3 while reading the following
description.
Flexible Disc Recording Fundamentals
To better understand the operation of the flexible disc drive, read this brief description of
disc recording principles. Refer to Figure 3-1 and 3-2 while reading this section.
The flexible magnetic media used with the 9130K disc drive measures 5.25 inches in
diameter. Both surfaces are coated with a ferromagnetic iron oxide. Both sides are used for
data storage. Each side contains 35 circular tracks. Each track is divided into 16 pie slice
shaped regions called sectors. Each sector can contain up to 256 bytes of data. Surface,
track and sector information is used to reference data location on the disc. Data is encoded
on the disc (ones and zeros) by changing the orientation of small magnetic dipoles in the
magnetic coating on the disc. There is no correlation between the magnetic polarity of the
dipoles and the ones and zeros. The ones and zeros are indicated by the location of the
dipole polarity transitions.
The disc is soft sectored, that is, there is no hardware indication of where each sector begins.
In order to allow soft sectoring, each sector is divided into two fields. For each sector there is
an ID field which contains information to identify the sector. Next there is a data field which
contains the actual data. Thus, the ID field serves as a fixed marker for the beginning of each
sector.
",..
, /
, /
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Figure 3-1:
ID and Data Field Content
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