The Disk - Tandy TRS-80 Owner Manual & Programming Manual

MEET YOUR
DISK
A LOOK
INSIDE
OF
IT
Although your disk looks
like
a
record,
it is
really
more
like
a multitude of tiny
magnets.
One
disk
can hold
more
than a million
magnetic
charges.
1,290,240 of
them
are
for
your information. That's
what we
mean when we
say a disk will hold
1,290,240
bits
or
161,280 bytes
of
information
(there
are eight
bits
in a
byte).
Some
of
these
bits
are
magnetically charged
and
some
aren't.
The
pattern
formed by
these
mag-
netic
charges
is
what's important.
It
forms a code
which
the
Computer can
read.
With more than a million
of
these
bits
on
a
disk,
you can appreciate
how
your
Computer must
orga-
nize
them
in
order
to find
anything.
It
does
this
by
building a
massive
disk
filing
system. First
it
cre-
ates
the
file
cabinets
by dividing
your
disk
into
"tracks."
Then
it
puts
drawers
in
the cabinets
by
dividing
each track into "sectors"
Then
. . .
we're
not finished
yet
.
. .
each
sector
is
divided into
bytes
and each byte
is
divided into
bits.
Note:
To be precise, there are
35
tracks
on a
disk,
18
sectors in
each
track,
256
bytes in
each
sector,
and 8
bits in
each
byte.
;
After creating this filing
system, the
Computer
puts a
master
directory
on
the
disk.
There,
it
indexes
where
everything
is
stored.
Whenever
it
wants
to find
something
—
a program, a
mailing
list,
your
letters
—
it
uses the directory
to find
the
tracks
and
sectors
where
it
is
stored.
It
can then
go
directly to
that
spot.
This
whole
filing
system
is,
of course,
what makes
the disk
system
so
powerful.
You
can
quickly find
anything you have
stored
on your
disk.
Putting
this filing
system on your
disk
is
called
"formatting"
it.
The
last
thing
we
had
you do
in
Chapter
1
was
to
insert
an "unformatted"
disk.
Before
you can use
it,
you
must
format
it
into
tracks
and
sectors.
FORMATTING A
DISK
How
do
you format
a disk? Well
.
. .
why
not just
tell
your
Computer
to
do
it?
If
you went through
the