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SYSTEM DESCRIPTION
24.2 -- File
St~ucture
files is that their content cannot load betow memory location
$20
if
they
are
to
reside in the single memory map of an
EXORciser I or EXORciser II system.
Binary
record
files
are
used
primarily
for
the
relocatable
obJect
data produced
by
the Macro Assembler and
the relocatable
FORTRAN
compiler;
however,
the
user
can
create data files using this binary record format as well.
ASCII
record
files
are
used
to
contain
all
other
MDOS-supported
data.
Such
files
can
be
in
either
space-compressed
or
non-space-compressed
rorm.
Normally,
MDOS
will
always
create
ASCII
files
with
the
space-comdression attribute to conserve diskette space.
The
non-memory-image
files
can be allocated in either
contiguous or segmented fashion.
Normally.
MDOS
~ill
create
such
files
in
a
segmented manner to take advantage of the
dynamic allocation scheme.
If
files are segmented,
theq
can
expand'to the full capacity of the diskette when they need to
grow
in
sizej
however,
if
files have
contiguously
allocated
space,
then
they can only be expanded
if
they
are
allocated
space that is contiguous to the originally
allocated
space.
Normally, contiguous files are created with the maximum space
that they
will ever need.
24.3
Record Structure
This section describes in detail the
two
record
types
supported
for diskette files.
In addition, a special record
t~pe
used for copying binary files to a
non-diskette
device
is
also
discussed.
The actual use of such records is fully
discussed in Chapter
25
which
describes
the
supported
I/O
functions.
All records supported
by MDOS
are terminated
by
a
carriage return,
line -Feed, and null
sequence;
however,
on
the
diskette,
only the carriage return character is retained
in
order to conserve diskette space.
When diskette files are
copied to a non-diskette device,
the other two characters are
automatically supplied by MDOS.
24.3.1
Binary records
Binary records
are
used primarily
as
output
-From
the
Macro
Assembler
and
the FORTRAN compiler, and Tor input to
the Linking Loader.
Binary records contain a special
~@co~d
header,
a
byte
count,
and
a checksum.
The checksum is a
two's-complemented sum of all bytes in the
record
from
the
byte
count through the last data byte,
inclusive.
A
maximum
~f
254
(decimal) data bytes can be contained in
each
binary
record.
The
-Format
of
a
binary
record can be illustrated as
Page
24-11
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