Theory Of Operation; The Diskette - Heath H89-17 Software Reference Manual

THEORY OF OPERATION
Although it is not absolutely essential that you
know the Theory of Operation for this system, a
basic knowledge of it will help you to use the
system more effectively. Read this information
before you proceed to the "System Set-Up Pro-
cedure". Refer to Appendix A, the "Glossary", in
Chapter
1,
for a definition of any unfamiliar
terms.
Configuration for the H89-17
I
0-7
A disk system combines many of the advantages of other types of data storage
systems. ltis not as fast as random-access memory, but for the same amount of
storage area it is much less expensive. On the other hand a disk system costs
more than a tape system for the same amount of storage, but it can locate a given
data record much more rapidly. Each type of data storage system has its advan-
tages. however, the disk system provides the most functional combinations for
everyday applications.
The Diskette
A diskette is a circular sheet of mylar coated with a magnetic oxide. As the
diskette rotates at
300
rpm, an electromagnetic head passes over the oxide
material, called the "medium", and interacts with it by means of a magnetic
field. This combination of head and medium is a lot like the magnetic tape
recorder you use to record and play music.
The medium consists of millions of tiny magnetic particles called "domains".
Each of these domains is magnetized in one direction or the other. The direction
in which a domain is magnetized describes the binary data stored on the diskette.
If the read/write head is "reading" information, it senses the direction in which
the domains in a given area are magnetized, and converts this information into
electric impulses which become binary bits. If the head is "writing" the opposite
happens; the bits are converted into electrical impulses, changing the magnetic
field around the head. This, in turn, magnetizes some of the domains in one
direction or the other, depending upon whether the bits are ones or zeros.
Each diskette can store
102,400
bytes of data, with each byte composed of eight
bits. The diskettes are divided into
40
tracks, circular rings, much like the
grooves in an LP record. Each track is subdivided into
10
sectors, giving a total of
400
sectors of
256
bytes each.