<s>
Job	B-Application
Control	I-Application
Language	I-Application
(	O
JCL	O
)	O
is	O
a	O
name	O
for	O
scripting	B-Language
languages	I-Language
used	O
on	O
IBM	B-Device
mainframe	I-Device
operating	B-General_Concept
systems	I-General_Concept
to	O
instruct	O
the	O
system	O
on	O
how	O
to	O
run	O
a	O
batch	B-General_Concept
job	I-General_Concept
or	O
start	O
a	O
subsystem	O
.	O
</s>
<s>
Parameters	O
in	O
the	O
JCL	O
can	O
also	O
provide	O
accounting	O
information	O
for	O
tracking	O
the	O
resources	O
used	O
by	O
a	O
job	B-Application
as	O
well	O
as	O
which	O
machine	O
the	O
job	B-Application
should	O
run	O
on	O
.	O
</s>
<s>
There	O
are	O
two	O
distinct	O
IBM	O
Job	B-Application
Control	I-Application
languages	I-Application
:	O
</s>
<s>
the	O
other	O
for	O
the	O
lineage	O
from	O
OS/360	B-Application
to	O
z/OS	B-Application
,	O
the	O
latter	O
now	O
including	O
JES	B-Application
extensions	O
,	O
Job	B-Application
Entry	I-Application
Control	I-Application
Language	I-Application
(	O
JECL	B-Application
)	O
.	O
</s>
<s>
The	O
VM	B-Application
operating	I-Application
system	I-Application
does	O
not	O
have	O
JCL	O
as	O
such	O
;	O
the	O
CP	B-Application
and	I-Application
CMS	I-Application
components	O
each	O
have	O
command	B-Language
languages	I-Language
.	O
</s>
<s>
Certain	O
words	O
or	O
phrases	O
used	O
in	O
conjunction	O
to	O
JCL	O
are	O
specific	O
to	O
IBM	B-Device
mainframe	I-Device
technology	O
.	O
</s>
<s>
Dataset	B-Application
:	O
a	O
"	O
dataset	B-Application
"	O
is	O
a	O
file	O
;	O
it	O
can	O
be	O
temporary	O
or	O
permanent	O
,	O
and	O
located	O
on	O
a	O
disk	O
drive	O
,	O
tape	B-Architecture
storage	I-Architecture
,	O
or	O
other	O
device	O
.	O
</s>
<s>
Member	O
:	O
a	O
"	O
member	O
"	O
of	O
a	O
partitioned	O
dataset	B-Application
(	O
PDS	O
)	O
is	O
an	O
individual	O
dataset	B-Application
within	O
a	O
PDS	O
.	O
</s>
<s>
Partitioned	O
dataset	B-Application
:	O
a	O
"	O
partitioned	O
dataset	B-Application
"	O
or	O
PDS	O
is	O
collection	O
of	O
members	O
,	O
or	O
archive	O
.	O
</s>
<s>
Partitioned	O
datasets	O
are	O
commonly	O
used	O
to	O
store	O
textual	O
data	O
such	O
as	O
source	O
code	O
,	O
assembler	B-Language
macros	B-Language
(	O
SYS1.MACLIB	O
)	O
,	O
system	O
configuration	O
(	O
SYS1.PARMLIB	O
)	O
,	O
reusable	O
JCL	O
procedures	O
(	O
SYS1.PROCLIB	O
)	O
,	O
etc	O
.	O
</s>
<s>
As	O
such	O
,	O
they	O
have	O
something	O
in	O
common	O
with	O
archive	O
files	O
(	O
ZIP	O
,	O
TAR	O
,	O
etc	O
)	O
and	O
with	O
directories	O
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
They	O
are	O
also	O
used	O
to	O
store	O
binary	O
code	O
(	O
load	O
modules	O
or	O
program	O
objects	O
)	O
;	O
in	O
that	O
guise	O
,	O
they	O
are	O
roughly	O
analogous	O
to	O
ar-based	B-Application
static	I-Application
libraries	I-Application
in	O
Unix-based	O
systems	O
.	O
</s>
<s>
Since	O
the	O
1989	O
release	O
of	O
MVS	O
DFP	O
3.2	O
,	O
PDSEs	O
(	O
Partitioned	O
Data	B-Application
Set	I-Application
Extended	O
)	O
have	O
existed	O
as	O
an	O
improved	O
version	O
of	O
PDS	O
;	O
from	O
the	O
user	O
or	O
application	O
programmer	O
viewpoint	O
,	O
they	O
are	O
largely	O
unchanged	O
(	O
save	O
the	O
removal	O
of	O
some	O
obscure	O
legacy	O
features	O
)	O
,	O
but	O
their	O
internal	O
implementation	O
is	O
very	O
different	O
.	O
</s>
<s>
USS	B-Operating_System
:	O
Unix	B-Operating_System
system	I-Operating_System
services	I-Operating_System
,	O
a	O
Unix	B-Application
subsystem	O
running	O
as	O
part	O
of	O
MVS	O
,	O
and	O
allowing	O
Unix	B-Application
files	O
,	O
scripts	O
,	O
tasks	O
,	O
and	O
programs	O
to	O
run	O
on	O
a	O
mainframe	O
in	O
a	O
UNIX	B-Application
environment	O
.	O
</s>
<s>
Originally	O
,	O
mainframe	O
systems	O
were	O
oriented	O
toward	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
Many	O
batch	B-General_Concept
jobs	I-General_Concept
require	O
setup	O
,	O
with	O
specific	O
requirements	O
for	O
main	O
storage	O
,	O
and	O
dedicated	O
devices	O
such	O
as	O
magnetic	O
tapes	O
,	O
private	O
disk	B-Application
volumes	I-Application
,	O
and	O
printers	O
set	O
up	O
with	O
special	O
forms	O
.	O
</s>
<s>
JCL	O
was	O
developed	O
as	O
a	O
means	O
of	O
ensuring	O
that	O
all	O
required	O
resources	O
are	O
available	O
before	O
a	O
job	B-Application
is	O
scheduled	O
to	O
run	O
.	O
</s>
<s>
For	O
example	O
,	O
many	O
systems	O
,	O
such	O
as	O
Linux	B-Application
allow	O
identification	O
of	O
required	O
datasets	O
to	O
be	O
specified	O
on	O
the	O
command	B-Application
line	I-Application
,	O
and	O
therefore	O
subject	O
to	O
substitution	O
by	O
the	O
shell	B-Operating_System
,	O
or	O
generated	O
by	O
the	O
program	O
at	O
run-time	O
.	O
</s>
<s>
On	O
these	O
systems	O
the	O
operating	B-General_Concept
system	I-General_Concept
job	B-General_Concept
scheduler	I-General_Concept
has	O
little	O
or	O
no	O
idea	O
of	O
the	O
requirements	O
of	O
the	O
job	B-Application
.	O
</s>
<s>
The	O
scheduler	O
can	O
pre-allocate	O
the	O
resources	O
prior	O
to	O
releasing	O
the	O
job	B-Application
to	O
run	O
.	O
</s>
<s>
This	O
helps	O
to	O
avoid	O
"	O
deadlock	B-Operating_System
"	O
,	O
where	O
job	B-Application
A	O
holds	O
resource	O
R1	O
and	O
requests	O
resource	O
R2	O
,	O
while	O
concurrently	O
running	O
job	B-Application
B	O
holds	O
resource	O
R2	O
and	O
requests	O
R1	O
.	O
</s>
<s>
With	O
job	B-Application
control	O
,	O
if	O
job	B-Application
A	O
is	O
scheduled	O
to	O
run	O
,	O
job	B-Application
B	O
will	O
not	O
be	O
started	O
until	O
job	B-Application
A	O
completes	O
or	O
releases	O
the	O
required	O
resources	O
.	O
</s>
<s>
For	O
both	O
DOS	O
and	O
OS	O
the	O
unit	O
of	O
work	O
is	O
the	O
job	B-Application
.	O
</s>
<s>
A	O
job	B-Application
consists	O
of	O
one	O
or	O
several	O
steps	O
,	O
each	O
of	O
which	O
is	O
a	O
request	O
to	O
run	O
one	O
specific	O
program	O
.	O
</s>
<s>
For	O
example	O
,	O
before	O
the	O
days	O
of	O
relational	B-Application
databases	I-Application
,	O
a	O
job	B-Application
to	O
produce	O
a	O
printed	O
report	O
for	O
management	O
might	O
consist	O
of	O
the	O
following	O
steps	O
:	O
a	O
user-written	O
program	O
to	O
select	O
the	O
appropriate	O
records	O
and	O
copy	O
them	O
to	O
a	O
temporary	O
file	O
;	O
sort	B-Algorithm
the	O
temporary	O
file	O
into	O
the	O
required	O
order	O
,	O
usually	O
using	O
a	O
general-purpose	O
utility	O
;	O
a	O
user-written	O
program	O
to	O
present	O
the	O
information	O
in	O
a	O
way	O
that	O
is	O
easy	O
for	O
the	O
end-users	O
to	O
read	O
and	O
includes	O
other	O
useful	O
information	O
such	O
as	O
sub-totals	O
;	O
and	O
a	O
user-written	O
program	O
to	O
format	O
selected	O
pages	O
of	O
the	O
end-user	O
information	O
for	O
display	O
on	O
a	O
monitor	O
or	O
terminal	O
.	O
</s>
<s>
In	O
both	O
DOS	O
and	O
OS	O
JCL	O
the	O
first	O
"	O
card	O
"	O
must	O
be	O
the	O
JOB	B-Application
card	O
,	O
which	O
:	O
</s>
<s>
Identifies	O
the	O
job	B-Application
.	O
</s>
<s>
Defines	O
how	O
the	O
job	B-Application
as	O
a	O
whole	O
is	O
to	O
be	O
run	O
,	O
e.g.	O
</s>
<s>
its	O
priority	O
relative	O
to	O
other	O
jobs	O
in	O
the	O
queue	B-Device
.	O
</s>
<s>
Procedures	O
(	O
commonly	O
called	O
procs	O
)	O
are	O
pre-written	O
JCL	O
for	O
steps	O
or	O
groups	O
of	O
steps	O
,	O
inserted	O
into	O
a	O
job	B-Application
.	O
</s>
<s>
Procs	O
are	O
used	O
for	O
repeating	O
steps	O
which	O
are	O
used	O
several	O
times	O
in	O
one	O
job	B-Application
,	O
or	O
in	O
several	O
different	O
jobs	O
.	O
</s>
<s>
Both	O
DOS	O
and	O
OS	O
JCL	O
have	O
a	O
maximum	O
usable	O
line	O
length	O
of	O
80	O
characters	O
,	O
because	O
when	O
DOS/360	O
and	O
OS/360	B-Application
were	O
first	O
used	O
the	O
main	O
method	O
of	O
providing	O
new	O
input	O
to	O
a	O
computer	O
system	O
was	O
80-column	O
punched	B-Architecture
cards	I-Architecture
.	O
</s>
<s>
It	O
later	O
became	O
possible	O
to	O
submit	O
jobs	O
via	O
disk	O
or	O
tape	O
files	O
with	O
longer	O
record	O
lengths	O
,	O
but	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
job	B-Application
submission	O
components	O
ignored	O
everything	O
after	O
character	O
80	O
.	O
</s>
<s>
Strictly	O
speaking	O
both	O
operating	B-General_Concept
system	I-General_Concept
families	O
use	O
only	O
71	O
characters	O
per	O
line	O
.	O
</s>
<s>
Characters	O
73-80	O
are	O
usually	O
card	O
sequence	O
numbers	O
which	O
the	O
system	O
printed	O
on	O
the	O
end-of-job	O
report	O
and	O
are	O
useful	O
for	O
identifying	O
the	O
locations	O
of	O
any	O
errors	O
reported	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
All	O
commands	O
,	O
parameter	O
names	O
and	O
values	O
have	O
to	O
be	O
in	O
capitals	O
,	O
except	O
for	O
USS	B-Operating_System
filenames	O
.	O
</s>
<s>
All	O
lines	O
except	O
for	O
in-stream	O
input	O
(	O
see	O
below	O
)	O
have	O
to	O
begin	O
with	O
a	O
slash	O
"	O
/	O
"	O
,	O
and	O
all	O
lines	O
which	O
the	O
operating	B-General_Concept
system	I-General_Concept
processes	O
have	O
to	O
begin	O
with	O
two	O
slashes	O
//	O
-	O
always	O
starting	O
in	O
the	O
first	O
column	O
.	O
</s>
<s>
"	O
cards	O
"	O
which	O
are	O
to	O
be	O
processed	O
by	O
the	O
application	O
program	O
rather	O
than	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Data	O
which	O
is	O
to	O
be	O
kept	O
for	O
a	O
long	O
time	O
will	O
normally	O
be	O
stored	O
on	O
disk	O
,	O
but	O
before	O
the	O
use	O
of	O
interactive	B-General_Concept
terminals	O
became	O
common	O
the	O
only	O
way	O
to	O
create	O
and	O
edit	O
such	O
disk	O
files	O
was	O
by	O
supplying	O
the	O
new	O
data	O
on	O
cards	O
.	O
</s>
<s>
This	O
makes	O
the	O
operating	B-General_Concept
system	I-General_Concept
resume	O
processing	O
JCL	O
in	O
the	O
card	O
following	O
the	O
/	O
*	O
card	O
.	O
</s>
<s>
OS	O
JCL	O
:	O
DD	B-Application
statements	O
can	O
be	O
used	O
to	O
describe	O
in-stream	O
data	O
,	O
as	O
well	O
as	O
data	B-Application
sets	I-Application
.	O
</s>
<s>
A	O
DD	B-Application
statement	O
dealing	O
with	O
in-stream	O
data	O
has	O
an	O
asterisk	O
( *	O
)	O
following	O
the	O
DD	B-Application
identifier	O
,	O
e.g.	O
</s>
<s>
//SYSIN	O
DD	B-Application
*	O
.	O
</s>
<s>
JCL	O
statements	O
can	O
be	O
included	O
as	O
part	O
of	O
in-stream	O
data	O
by	O
using	O
the	O
DD	B-Application
DATA	O
statements	O
.	O
</s>
<s>
Specifying	O
an	O
alternate	O
delimiter	O
allows	O
JCL	O
to	O
be	O
read	O
as	O
data	O
,	O
for	O
example	O
to	O
copy	O
procedures	O
to	O
a	O
library	O
member	O
or	O
to	O
submit	O
a	O
job	B-Application
to	O
the	O
internal	O
reader	O
.	O
</s>
<s>
An	O
example	O
,	O
which	O
submits	O
a	O
job	B-Application
to	O
the	O
Internal	O
Reader	O
(	O
INTRDR	O
)	O
and	O
then	O
deletes	O
two	O
files	O
is	O
:	O
</s>
<s>
The	O
program	O
called	O
IEFBR14	B-Application
will	O
run	O
NOW	O
and	O
upon	O
completion	O
,	O
the	O
two	O
existing	O
files	O
,	O
PICALC.4DGTS	O
and	O
PICALC.5DGTS	O
will	O
be	O
deleted	O
.	O
</s>
<s>
Much	O
of	O
the	O
complexity	O
of	O
OS	O
JCL	O
,	O
in	O
particular	O
,	O
derives	O
from	O
the	O
large	O
number	O
of	O
options	O
for	O
specifying	O
dataset	B-Application
information	O
.	O
</s>
<s>
While	O
files	O
on	O
Unix-like	O
operating	B-General_Concept
systems	I-General_Concept
are	O
abstracted	O
into	O
ordered	O
streams	O
of	O
bytes	O
,	O
with	O
the	O
task	O
of	O
reading	O
and	O
writing	O
structured	O
data	O
belonging	O
exclusively	O
with	O
user-level	O
programs	O
(	O
which	O
,	O
ultimately	O
,	O
ingest	O
and	O
emit	O
such	O
streams	O
)	O
,	O
and	O
the	O
practical	O
details	O
of	O
data	O
storage	O
and	O
access	O
handled	O
in	O
large	O
part	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
without	O
the	O
knowledge	O
of	O
user	O
programs	O
;	O
datasets	O
on	O
OS/360	B-Application
and	O
its	O
successors	O
expose	O
their	O
file	O
types	O
and	O
sizes	O
,	O
record	O
types	O
and	O
lengths	O
,	O
block	O
sizes	O
,	O
device-specific	O
information	O
like	O
magnetic	B-Architecture
tape	I-Architecture
density	O
,	O
and	O
label	O
information	O
.	O
</s>
<s>
For	O
example	O
,	O
to	O
copy	B-Application
a	I-Application
file	I-Application
on	O
Unix	B-Application
operating	I-Application
system	I-Application
,	O
the	O
user	O
would	O
enter	O
a	O
command	O
like	O
:	O
</s>
<s>
The	O
following	O
example	O
,	O
using	O
JCL	O
,	O
might	O
be	O
used	O
to	O
copy	B-Application
a	I-Application
file	I-Application
on	O
OS/360	B-Application
:	O
</s>
<s>
A	O
second	O
explanation	O
for	O
the	O
complexity	O
of	O
JCL	O
is	O
the	O
different	O
expectations	O
for	O
running	O
a	O
job	B-Application
from	O
those	O
found	O
in	O
a	O
PC	B-Device
or	O
Unix-like	O
environment	O
.	O
</s>
<s>
Low-end	O
System/360	B-Application
CPUs	O
were	O
less	O
powerful	O
and	O
more	O
expensive	O
than	O
the	O
mid-1980s	O
PCs	O
for	O
which	O
MS-DOS	O
was	O
designed	O
.	O
</s>
<s>
OS/360	B-Application
was	O
intended	O
for	O
systems	O
with	O
a	O
minimum	O
memory	O
size	O
of	O
32KB	O
and	O
DOS/360	O
for	O
systems	O
with	O
a	O
minimum	O
of	O
16KB	O
.	O
</s>
<s>
A	O
360/30	B-Device
CPUlow-end	O
when	O
System/360	B-Application
was	O
announced	O
in	O
1964processed	O
1.8K	O
to	O
34.5K	O
instructions	O
per	O
second	O
.	O
</s>
<s>
The	O
first	O
IBM	B-Device
PC	I-Device
in	O
1981	O
had	O
16KB	O
or	O
64KB	O
of	O
memory	O
and	O
would	O
process	O
about	O
330K	O
instructions	O
per	O
second	O
.	O
</s>
<s>
JCL	O
was	O
designed	O
for	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
As	O
such	O
,	O
it	O
has	O
to	O
tell	O
the	O
operating	B-General_Concept
system	I-General_Concept
everything	O
,	O
including	O
what	O
to	O
do	O
depending	O
on	O
the	O
result	O
of	O
a	O
step	O
.	O
</s>
<s>
Programs	O
run	O
on	O
a	O
PC	B-Device
frequently	O
depend	O
on	O
the	O
user	O
to	O
clean	O
up	O
after	O
processing	O
problems	O
.	O
</s>
<s>
System/360	B-Application
machines	O
were	O
designed	O
to	O
be	O
shared	O
by	O
all	O
the	O
users	O
in	O
an	O
organization	O
.	O
</s>
<s>
So	O
the	O
JOB	B-Application
card	O
tells	O
the	O
operating	B-General_Concept
system	I-General_Concept
how	O
to	O
bill	O
the	O
user	O
's	O
account	O
(	O
IS198T30500	O
)	O
,	O
what	O
predefined	O
amount	O
of	O
storage	O
and	O
other	O
resources	O
may	O
be	O
allocated	O
(	O
CLASS	O
=	O
L	O
)	O
,	O
and	O
several	O
other	O
things	O
.	O
</s>
<s>
DISP	O
=	O
SHR	O
tells	O
the	O
operating	B-General_Concept
system	I-General_Concept
that	O
other	O
programs	O
can	O
read	O
OLDFILE	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Later	O
versions	O
of	O
the	O
DOS/360	O
and	O
OS/360	B-Application
operating	B-General_Concept
systems	I-General_Concept
retain	O
most	O
features	O
of	O
the	O
original	O
JCLalthough	O
some	O
simplification	O
has	O
been	O
made	O
,	O
to	O
avoid	O
forcing	O
customers	O
to	O
rewrite	O
all	O
their	O
JCL	O
files	O
.	O
</s>
<s>
The	O
syntax	O
of	O
OS	O
JCL	O
is	O
similar	O
to	O
the	O
syntax	O
of	O
macros	B-Language
in	O
System/360	B-Application
assembly	B-Language
language	I-Language
,	O
and	O
would	O
therefore	O
have	O
been	O
familiar	O
to	O
programmers	O
at	O
a	O
time	O
when	O
many	O
programs	O
were	O
coded	O
in	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
In	O
the	O
example	O
the	O
ASSGN	O
,	O
DLBL	O
and	O
EXTENT	O
statements	O
do	O
the	O
same	O
work	O
(	O
specifying	O
where	O
a	O
new	O
disk	O
file	O
should	O
be	O
stored	O
)	O
as	O
a	O
single	O
DD	B-Application
statement	O
in	O
OS	O
JCL	O
.	O
</s>
<s>
In	O
the	O
original	O
DOS/360	O
and	O
in	O
most	O
versions	O
of	O
DOS/VS	O
one	O
had	O
to	O
specify	O
the	O
model	O
number	O
of	O
the	O
device	O
which	O
was	O
to	O
be	O
used	O
for	O
each	O
disk	O
or	O
tape	O
fileeven	O
for	O
existing	O
files	O
and	O
for	O
temporary	O
files	O
which	O
would	O
be	O
deleted	O
at	O
the	O
end	O
of	O
the	O
job	B-Application
.	O
</s>
<s>
DOS/360	O
originally	O
required	O
the	O
programmer	O
to	O
specify	O
the	O
location	O
and	O
size	O
of	O
all	O
files	O
on	O
DASD	B-Application
.	O
</s>
<s>
For	O
z/VSE	B-Application
a	O
file	O
can	O
have	O
up	O
to	O
256	O
extents	O
on	O
different	O
volumes	O
.	O
</s>
<s>
JOB	B-Application
statement	I-Application
,	O
which	O
identifies	O
the	O
start	O
of	O
the	O
job	B-Application
,	O
and	O
information	O
about	O
the	O
whole	O
job	B-Application
,	O
such	O
as	O
billing	O
,	O
run	O
priority	O
,	O
and	O
time	O
and	O
space	O
limits	O
.	O
</s>
<s>
EXEC	O
statement	O
,	O
which	O
identifies	O
the	O
program	O
or	O
procedure	O
to	O
be	O
executed	O
in	O
this	O
step	O
of	O
the	O
job	B-Application
,	O
and	O
information	O
about	O
the	O
step	O
,	O
including	O
CONDitions	O
for	O
running	O
or	O
skipping	O
a	O
step	O
.	O
</s>
<s>
DD	B-Application
(	O
Data	O
Definition	O
)	O
statements	O
,	O
which	O
identify	O
a	O
data	O
file	O
to	O
be	O
used	O
in	O
a	O
step	O
,	O
and	O
detailed	O
info	O
about	O
that	O
file	O
.	O
</s>
<s>
DD	B-Application
statements	O
can	O
be	O
in	O
any	O
order	O
within	O
the	O
step	O
.	O
</s>
<s>
Right	O
from	O
the	O
start	O
,	O
JCL	O
for	O
the	O
OS	O
family	O
(	O
up	O
to	O
and	O
including	O
z/OS	B-Application
)	O
was	O
more	O
flexible	O
and	O
easier	O
to	O
use	O
.	O
</s>
<s>
The	O
following	O
examples	O
use	O
the	O
old	O
style	O
of	O
syntax	O
which	O
was	O
provided	O
right	O
from	O
the	O
launch	O
of	O
System/360	B-Application
in	O
1964	O
.	O
</s>
<s>
The	O
operation	O
will	O
be	O
one	O
of	O
JOB	B-Application
,	O
EXEC	O
and	O
DD	B-Application
.	O
</s>
<s>
The	O
parameter	O
field	O
contains	O
parameters	O
which	O
are	O
keywords	O
that	O
used	O
in	O
the	O
statement	O
to	O
provide	O
information	O
such	O
as	O
the	O
program	O
or	O
dataset	B-Application
name	O
.	O
</s>
<s>
The	O
DD	B-Application
statement	O
is	O
used	O
to	O
reference	O
data	O
.	O
</s>
<s>
This	O
statement	O
links	O
a	O
program	O
's	O
internal	O
description	O
of	O
a	O
dataset	B-Application
to	O
the	O
data	O
on	O
external	O
devices	O
:	O
disks	O
,	O
tapes	O
,	O
cards	O
,	O
printers	O
,	O
etc	O
.	O
</s>
<s>
The	O
DD	B-Application
may	O
provide	O
information	O
such	O
as	O
a	O
device	O
type	O
(	O
e.g.	O
</s>
<s>
'	O
181	O
 '	O
,	O
'	O
2400-5	O
'	O
,	O
'	O
TAPE	O
 '	O
)	O
,	O
a	O
volume	B-Application
serial	I-Application
number	O
for	O
tapes	O
or	O
disks	O
,	O
and	O
the	O
description	O
of	O
the	O
data	O
file	O
,	O
called	O
the	O
DCB	O
subparameter	O
after	O
the	O
Data	B-Application
Control	I-Application
Block	I-Application
(	O
DCB	O
)	O
in	O
the	O
program	O
used	O
to	O
identify	O
the	O
file	O
.	O
</s>
<s>
Information	O
describing	O
the	O
file	O
can	O
come	O
from	O
three	O
sources	O
:	O
The	O
DD	B-Application
card	O
information	O
,	O
the	O
dataset	B-Application
label	O
information	O
for	O
an	O
existing	O
file	O
stored	O
on	O
tape	O
or	O
disk	O
,	O
and	O
the	O
DCB	O
macro	O
coded	O
in	O
the	O
program	O
.	O
</s>
<s>
When	O
the	O
file	O
is	O
opened	O
this	O
data	O
is	O
merged	O
,	O
with	O
the	O
DD	B-Application
information	O
taking	O
precedence	O
over	O
the	O
label	O
information	O
,	O
and	O
the	O
DCB	O
information	O
taking	O
precedence	O
over	O
both	O
.	O
</s>
<s>
The	O
updated	O
description	O
is	O
then	O
written	O
back	O
to	O
the	O
dataset	B-Application
label	O
.	O
</s>
<s>
Because	O
of	O
the	O
parameters	O
listed	O
above	O
and	O
specific	O
information	O
for	O
various	O
access	O
methods	O
and	O
devices	O
the	O
DD	B-Application
statement	O
is	O
the	O
most	O
complex	O
JCL	O
statement	O
.	O
</s>
<s>
In	O
one	O
IBM	O
reference	O
manual	O
description	O
of	O
the	O
DD	B-Application
statement	O
occupies	O
over	O
130	O
pages	O
—	O
more	O
than	O
twice	O
as	O
much	O
as	O
the	O
JOB	B-Application
and	O
EXEC	O
statements	O
combined	O
.	O
</s>
<s>
The	O
DD	B-Application
statement	O
allows	O
inline	O
data	O
to	O
be	O
injected	O
into	O
the	O
job	B-Application
stream	I-Application
.	O
</s>
<s>
This	O
is	O
useful	O
for	O
providing	O
control	O
information	O
to	O
utilities	O
such	O
as	O
IDCAMS	O
,	O
SORT	B-Algorithm
,	O
etc	O
.	O
</s>
<s>
From	O
the	O
very	O
beginning	O
,	O
the	O
JCL	O
for	O
the	O
OS	O
family	O
of	O
operating	B-General_Concept
systems	I-General_Concept
offered	O
a	O
high	O
degree	O
of	O
device	O
independence	O
.	O
</s>
<s>
Even	O
for	O
new	O
files	O
which	O
were	O
to	O
be	O
kept	O
after	O
the	O
end	O
of	O
the	O
job	B-Application
one	O
could	O
specify	O
the	O
device	O
type	O
in	O
generic	O
terms	O
,	O
e.g.	O
,	O
UNIT	O
=D	O
ISK	O
,	O
UNIT	O
=	O
TAPE	O
,	O
or	O
UNIT	O
=	O
SYSSQ	O
(	O
tape	O
or	O
disk	O
)	O
.	O
</s>
<s>
Procedures	O
can	O
also	O
be	O
included	O
in	O
the	O
job	B-Application
stream	I-Application
by	O
terminating	O
the	O
procedure	O
with	O
a	O
//	O
PEND	O
statement	O
,	O
then	O
invoking	O
it	O
by	O
name	O
the	O
same	O
was	O
as	O
if	O
it	O
were	O
in	O
a	O
procedure	O
library	O
.	O
</s>
<s>
OS	O
JCL	O
procedures	O
were	O
parameterized	O
from	O
the	O
start	O
,	O
making	O
them	O
rather	O
like	O
macros	B-Language
or	O
even	O
simple	O
subroutines	O
and	O
thus	O
increasing	O
their	O
reusability	O
in	O
a	O
wide	O
range	O
of	O
situations	O
.	O
</s>
<s>
In	O
this	O
example	O
,	O
all	O
the	O
values	O
beginning	O
with	O
ampersands	O
"	O
&	O
"	O
are	O
parameters	O
which	O
will	O
be	O
specified	O
when	O
a	O
job	B-Application
requests	O
that	O
the	O
procedure	O
be	O
used	O
.	O
</s>
<s>
Here	O
,	O
MYPR02	O
uses	O
the	O
file	O
identified	O
as	O
NEWFILE	O
in	O
step	O
MYPR01	O
(	O
DSN	O
means	O
"	O
dataset	B-Application
name	O
"	O
and	O
specifies	O
the	O
name	O
of	O
the	O
file	O
;	O
a	O
DSN	O
could	O
not	O
exceed	O
44	O
characters	O
)	O
.	O
</s>
<s>
In	O
jobs	O
which	O
contain	O
a	O
mixture	O
of	O
job-specific	O
JCL	O
and	O
procedure	O
calls	O
,	O
a	O
job-specific	O
step	O
can	O
refer	O
back	O
to	O
a	O
file	O
which	O
was	O
fully	O
specified	O
in	O
a	O
procedure	O
,	O
for	O
example	O
:	O
</s>
<s>
where	O
DSN	O
=	O
*	O
.STEP01.MYPR01.NEWFILE	O
means	O
"	O
use	O
the	O
file	O
identified	O
as	O
NEWFILE	O
in	O
step	O
MYPR01	O
of	O
the	O
procedure	O
used	O
by	O
step	O
STEP01	O
of	O
this	O
job	B-Application
"	O
.	O
</s>
<s>
Using	O
the	O
name	O
of	O
the	O
step	O
which	O
called	O
the	O
procedure	O
rather	O
than	O
the	O
name	O
of	O
the	O
procedure	O
allows	O
a	O
programmer	O
to	O
use	O
the	O
same	O
procedure	O
several	O
times	O
in	O
the	O
same	O
job	B-Application
without	O
confusion	O
about	O
which	O
instance	O
of	O
the	O
procedure	O
is	O
used	O
in	O
the	O
referback	O
.	O
</s>
<s>
In	O
early	O
versions	O
of	O
the	O
OS	O
(	O
certainly	O
before	O
OS/360	B-Application
R21.8	O
)	O
the	O
block	O
length	O
must	O
be	O
in	O
decreasing	O
order	O
,	O
or	O
the	O
user	O
must	O
inspect	O
each	O
instance	O
and	O
append	O
to	O
the	O
named	O
DD	B-Application
statement	O
the	O
maximum	O
block	O
length	O
found	O
,	O
as	O
in	O
,	O
for	O
example	O
,	O
</s>
<s>
A	O
usual	O
fallback	O
was	O
to	O
simply	O
determine	O
the	O
maximum	O
possible	O
block	O
length	O
on	O
the	O
device	O
,	O
and	O
specify	O
that	O
on	O
the	O
named	O
DD	B-Application
statement	O
,	O
as	O
in	O
,	O
for	O
example	O
,	O
</s>
<s>
This	O
translates	O
to	O
the	O
following	O
pseudocode	B-Language
:	O
</s>
<s>
The	O
COND	O
parameter	O
may	O
also	O
be	O
specified	O
on	O
the	O
JOB	B-Application
statement	I-Application
.	O
</s>
<s>
If	O
so	O
the	O
system	O
"	O
performs	O
the	O
same	O
return	O
code	O
tests	O
for	O
every	O
step	O
in	O
a	O
job	B-Application
.	O
</s>
<s>
If	O
a	O
JOB	B-Application
statement	I-Application
return	O
code	O
test	O
is	O
satisfied	O
,	O
the	O
job	B-Application
terminates.	O
"	O
</s>
<s>
Jobs	O
use	O
a	O
number	O
of	O
IBM	B-Application
utility	I-Application
programs	I-Application
to	O
assist	O
in	O
the	O
processing	O
of	O
data	O
.	O
</s>
<s>
Utilities	O
are	O
most	O
useful	O
in	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
Data	B-Application
Set	I-Application
Utilities	O
-	O
Create	O
,	O
print	O
,	O
copy	O
,	O
move	O
and	O
delete	O
data	B-Application
sets	I-Application
.	O
</s>
<s>
Access	B-Application
Method	I-Application
Services	I-Application
-	O
Process	O
Virtual	B-Application
Storage	I-Application
Access	I-Application
Method	I-Application
(	O
VSAM	O
)	O
and	O
non-VSAM	O
data	B-Application
sets	I-Application
.	O
</s>
<s>
As	O
one	O
instructional	O
book	O
on	O
JCL	O
asked	O
,	O
"	O
Why	O
do	O
even	O
sophisticated	O
programmers	O
hesitate	O
when	O
it	O
comes	O
to	O
Job	B-Application
Control	I-Application
Language	I-Application
?	O
"	O
</s>
<s>
As	O
one	O
Fortran	O
IV	O
textbook	O
said	O
when	O
listing	O
possible	O
error	O
messages	O
from	O
the	O
WATFOR	B-Language
compiler	O
:	O
"	O
Have	O
you	O
been	O
so	O
foolish	O
as	O
to	O
try	O
to	O
write	O
your	O
own	O
'	O
DD	B-Application
 '	O
system	O
control	O
cards	O
?	O
</s>
<s>
On	O
IBM	B-Device
mainframe	I-Device
systems	O
Job	B-Application
Entry	I-Application
Control	I-Application
Language	I-Application
or	O
JECL	B-Application
is	O
the	O
set	O
of	O
command	B-Language
language	I-Language
control	O
statements	O
that	O
provide	O
information	O
for	O
the	O
spooling	B-Device
subsystem	O
JES2	B-Application
or	I-Application
JES3	I-Application
on	O
z/OS	B-Application
or	O
VSE/POWER	O
for	O
z/VSE	B-Application
.	O
</s>
<s>
JECL	B-Application
statements	O
may	O
"	O
specify	O
on	O
which	O
network	O
computer	O
to	O
run	O
the	O
job	B-Application
,	O
when	O
to	O
run	O
the	O
job	B-Application
,	O
and	O
where	O
to	O
send	O
the	O
resulting	O
output.	O
"	O
</s>
<s>
JECL	B-Application
is	O
distinct	O
from	O
job	B-Application
control	I-Application
language	I-Application
(	O
JCL	O
)	O
,	O
which	O
instructs	O
the	O
operating	B-General_Concept
system	I-General_Concept
how	O
to	O
run	O
the	O
job	B-Application
.	O
</s>
<s>
There	O
are	O
different	O
versions	O
of	O
JECL	B-Application
for	O
the	O
three	O
environments	O
.	O
</s>
<s>
An	O
early	O
version	O
of	O
Job	B-Application
Entry	I-Application
Control	I-Application
Language	I-Application
for	O
OS/360	B-Application
Remote	O
Job	B-Application
Entry	O
(	O
Program	O
Number	O
360S-RC-536	O
)	O
used	O
the	O
identifier	O
..	O
in	O
columns	O
12	O
of	O
the	O
input	O
record	O
and	O
consisted	O
of	O
a	O
single	O
control	O
statement	O
:	O
JED	O
(	O
Job	B-Application
Entry	O
Definition	O
)	O
.	O
</s>
<s>
Although	O
the	O
term	O
had	O
not	O
yet	O
been	O
developed	O
,	O
HASP	B-Application
did	O
have	O
similar	O
functionality	O
to	O
what	O
would	O
become	O
the	O
JECL	B-Application
of	O
JES	B-Application
,	O
including	O
/	O
*	O
syntax	O
.	O
</s>
<s>
For	O
JES2	B-Application
JECL	B-Application
statements	O
start	O
with	O
/	O
*	O
,	O
for	O
JES3	B-Application
they	O
start	O
with	O
//	O
*	O
,	O
except	O
for	O
remote	O
/	O
*SIGNON	O
and	O
/	O
*SIGNOFF	O
commands	O
.	O
</s>
<s>
The	O
following	O
JES2	B-Application
JECL	B-Application
statements	O
are	O
used	O
in	O
z/OS	B-Application
1.2.0	O
.	O
</s>
<s>
For	O
VSE	B-Application
JECL	B-Application
statements	O
start	O
with	O
'	O
*	O
$$	O
 '	O
(	O
note	O
the	O
single	O
space	O
)	O
.	O
</s>
<s>
The	O
Job	B-Application
Entry	I-Application
Control	I-Application
Language	I-Application
defines	O
the	O
start	O
and	O
end	O
lines	O
of	O
JCL	O
jobs	O
.	O
</s>
<s>
It	O
advises	O
VSE/POWER	O
how	O
this	O
job	B-Application
is	O
handled	O
.	O
</s>
<s>
JECL	B-Application
statements	O
define	O
the	O
job	B-Application
name	O
(	O
used	O
by	O
VSE/POWER	O
)	O
,	O
the	O
class	O
in	O
which	O
the	O
job	B-Application
is	O
processed	O
,	O
and	O
the	O
disposition	O
of	O
the	O
job	B-Application
(	O
i.e.	O
</s>
<s>
Other	O
mainframe	O
batch	B-General_Concept
systems	I-General_Concept
had	O
some	O
form	O
of	O
job	B-Application
control	I-Application
language	I-Application
,	O
whether	O
called	O
that	O
or	O
not	O
;	O
their	O
syntax	O
was	O
completely	O
different	O
from	O
IBM	O
versions	O
,	O
but	O
they	O
usually	O
provided	O
similar	O
capabilities	O
.	O
</s>
<s>
include	O
"	O
command	B-Language
languages	I-Language
"	O
command	O
files	O
(	O
such	O
as	O
PCDOS	O
"	O
.bat	O
"	O
files	O
)	O
can	O
be	O
run	O
non-interactively	O
,	O
but	O
these	O
usually	O
do	O
not	O
provide	O
as	O
robust	O
an	O
environment	O
for	O
running	O
unattended	O
jobs	O
as	O
JCL	O
.	O
</s>
<s>
On	O
some	O
computer	O
systems	O
the	O
job	B-Application
control	I-Application
language	I-Application
and	O
the	O
interactive	B-General_Concept
command	B-Language
language	I-Language
may	O
be	O
different	O
.	O
</s>
<s>
For	O
example	O
,	O
TSO	B-Application
on	O
z/OS	B-Application
systems	O
uses	O
CLIST	B-Operating_System
or	O
Rexx	B-Language
as	O
command	B-Language
languages	I-Language
along	O
with	O
JCL	O
for	O
batch	B-General_Concept
work	O
.	O
</s>
