Radio Shack TRS-80 Trsdos & Disk Basic Reference Manual page 88

DISK BASIC
Introduction
DISK BASIC
is
a set
of
enhancements
to
LEVEL
II
BASIC,
plus
features to
allow disk input/output of
BASIC
programs and
data.
It is
a
memory
image
file
stored
on
the
TRSDOS
software diskette
with the
name BASIC
and
extension
/CMD.
When DISK BASIC
is
loaded
into
RAM,
it
automatically takes
control of the
LEVEL
II
BASIC
ROM
program, using
almost
all
of
its
routines
and adding
others.
This
is
possible
because
LEVEL
II
was designed with
upward
compatibility
built-in.
(You
can
see this
by examining the
memory map
for
LEVEL
II,
in particular,
hex
addresses
37DE-37EC.)
When
loaded,
DISK BASIC
occupies
approximately
5.8K
bytes of
RAM,
beginning
at
hex address
5200 (decimal 20992).
To
load
and
execute
DISK
BASIC,
first
power-up
the
Disk Operating
System
(see
System Operation), so that
DOS READY
is
displayed.
Now
type:
basic
HUES
TRSDOS
will
load
BASIC
into
RAM,
and
BASIC
will
begin the
"initialization
dialog".
This
is
a series
of questions
and answers
which
tell
BASIC how
to
organize
memory
according
to
your
needs.
The
first
question
is,
HOW MANY
FILES?.
You
repond with the
maximum number
of disk
files
that
will
be
open
(in
use)
at
any one time
-
any
number from
zero to
15.
(Every
program
or data
set
you
store
on
the disk
is
referred to as a
"file".
In
fact,
everything
on
the
disk,
including
system software,
exists in
the
form
of
files.)
The number you
enter
tells
BASIC how many
disk
I/O buffers and
data control blocks to create (for definitions, see Glossary). If
n
files
are to
be
in
use
at
once, then n buffers
will
be
required.
Each
buffer
will
take
290
bytes
from your
available
RAM
(256 for
the buffer plus
34
for a
data control block
[DCB]
),
so
don't enter an unnecessarily
large
number.
If
you
simply press
I3^M3;1 without
entering a
number,
BASIC
will
use
a
default value of
3
;
so you'll
be
able to
have
3
file
buffers
in
use
at
once.
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