Tandy TRS-80 Owner Manual & Programming Manual page 33

ONE
THING AT
A
TIME
(Sequential
Access
to
a
File)
A
tape
is
simple. There's only
one
way
to
put data
on
it
and one
way
to
read
it off.
A
disk
is
more
com-
plex.
There
are several
ways
to "file"
your data on
it.
In this
chapter
and
the next,
we'll
show
how
to
write
a
program which
stores
data
in a "sequential
access" disk
file. It's
the simplest
file
to
create
and
is
actually
very similar
to
a tape
"file"
In
Chapter
7,
we'll
introduce
"direct access,"
an
alternate
type
of disk
file.
In
showing
how
to store
things
on
disk, we'll
fre-
quently use the
words
disk
file
and
disk
directory.
We
discussed these concepts in
Chapter
2,
but
we'll
summarize them
now.
Everything you
store
on
disk
must
go
in
a
disk
file
and
be assigned a filename.
Your Computer
will
index the location
of
the disk
file
in
the
disk's
directory.
For example,
if
you want
to store
the
names
of
your
friends,
you
could put
them
in a
disk
file
named
"FRIENDS'' Your
disk's directory
would then index where, on the
disk,
"FRIENDS"
is
stored.
There
is,
of course, a
good reason
for
all
of
this.
Using
the disk
filing
system, the
Computer
will
be
able
to
immediately
find
any
file
on
the
disk.
WRITING
A
DISK FILE
Let's
assume you want
to
"write"
your
checks on
the
disk:
CHECKS
DR.
HORN
SAFEWAY
FIRST
CHRISTIAN
OFFICE
SUPPLY
Weil
start
with a
short,
simple program which
writes the
first
check,
"DR.
HORN|'
on
the
disk.
Insert
a formatted disk
in
your
disk
drive.
(If
you
have
more
than one
disk
drive,
use
drive
0.)
25