<s>
IEFBR14	B-Application
is	O
an	O
IBM	O
mainframe	B-Architecture
utility	B-Application
program	I-Application
.	O
</s>
<s>
It	O
runs	O
in	O
all	O
IBM	O
mainframe	B-Architecture
environments	O
derived	O
from	O
OS/360	B-Application
,	O
including	O
z/OS	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
placeholder	O
that	O
returns	O
the	O
exit	B-Operating_System
status	I-Operating_System
zero	O
,	O
similar	O
to	O
the	O
true	B-Device
command	O
on	O
UNIX-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
On	O
OS/360	B-Application
and	O
derived	O
mainframe	B-Architecture
systems	O
,	O
most	O
programs	O
never	O
specify	O
files	O
(	O
usually	O
called	O
datasets	O
)	O
directly	O
,	O
but	O
instead	O
reference	O
them	O
indirectly	O
through	O
the	O
Job	B-Application
Control	I-Application
Language	I-Application
(	O
JCL	B-Application
)	O
statements	O
that	O
invoke	O
the	O
programs	O
.	O
</s>
<s>
IEFBR14	B-Application
was	O
created	O
because	O
while	O
DD	O
statements	O
can	O
create	O
or	O
delete	O
files	O
easily	O
,	O
they	O
cannot	O
do	O
so	O
without	O
a	O
program	O
to	O
be	O
run	O
due	O
to	O
a	O
certain	O
peculiarity	O
of	O
the	O
Job	O
Management	O
system	O
,	O
which	O
always	O
requires	O
that	O
the	O
Initiator	O
actually	O
execute	O
a	O
program	O
,	O
even	O
if	O
that	O
program	O
is	O
effectively	O
a	O
null	O
statement	O
.	O
</s>
<s>
The	O
program	O
used	O
in	O
the	O
JCL	B-Application
does	O
not	O
actually	O
need	O
to	O
use	O
the	O
files	O
to	O
cause	O
their	O
creation	O
or	O
deletion	O
the	O
DD	O
DISP	O
=	O
...	O
specification	O
does	O
all	O
the	O
work	O
.	O
</s>
<s>
IEFBR14	B-Application
can	O
thus	O
be	O
used	O
to	O
create	O
or	O
delete	O
a	O
data	B-Application
set	I-Application
using	O
JCL	B-Application
.	O
</s>
<s>
A	O
secondary	O
reason	O
to	O
run	O
IEFBR14	B-Application
was	O
to	O
unmount	O
devices	O
(	O
usually	O
tapes	O
or	O
disks	O
)	O
that	O
had	O
been	O
left	O
mounted	O
from	O
a	O
previous	O
job	O
,	O
perhaps	O
because	O
of	O
an	O
error	O
in	O
that	O
job	O
's	O
JCL	B-Application
or	O
because	O
the	O
job	O
ended	O
in	O
error	O
.	O
</s>
<s>
At	O
least	O
on	O
z/OS	B-Application
,	O
branching	O
off	O
to	O
execute	O
another	O
program	O
would	O
cause	O
the	O
calling	O
program	O
to	O
be	O
evaluated	O
for	O
syntax	O
errors	O
at	O
that	O
point	O
.	O
</s>
<s>
The	O
"	O
IEF	O
"	O
derives	O
from	O
a	O
convention	O
on	O
mainframe	B-Architecture
computers	I-Architecture
that	O
programs	O
supplied	O
by	O
IBM	O
were	O
grouped	O
together	O
by	O
function	O
or	O
creator	O
and	O
that	O
each	O
group	O
shared	O
a	O
three-letter	O
prefix	O
.	O
</s>
<s>
In	O
OS/360	B-Application
,	O
the	O
first	O
letter	O
was	O
almost	O
always	O
"	O
I	O
"	O
,	O
and	O
the	O
programs	O
produced	O
by	O
the	O
Job	O
Management	O
group	O
(	O
including	O
IEFBR14	B-Application
)	O
all	O
used	O
the	O
prefix	O
"	O
IEF	O
"	O
.	O
</s>
<s>
Other	O
common	O
prefixes	O
included	O
"	O
IEB	O
"	O
for	O
dataset	B-Application
utility	O
programs	O
,	O
"	O
IEH	O
"	O
for	O
system	O
utility	O
programs	O
,	O
and	O
"	O
IEW	O
"	O
for	O
program	O
linkage	O
and	O
loading	O
.	O
</s>
<s>
Other	O
major	O
components	O
were	O
(	O
and	O
still	O
are	O
)	O
"	O
IEA	O
"	O
(	O
Operating	O
System	O
Supervisor	O
)	O
and	O
"	O
IEC	O
"	O
(	O
Input/Output	B-Application
Supervisor	I-Application
)	O
.	O
</s>
<s>
This	O
portion	O
of	O
a	O
program	O
name	O
was	O
often	O
mnemonic	O
for	O
example	O
,	O
IEBUPDTE	O
was	O
the	O
dataset	B-Application
utility	O
(	O
IEB	O
)	O
that	O
applied	O
updates	O
(	O
UPDTE	O
)	O
to	O
source	O
code	O
files	O
,	O
and	O
IEHINITT	O
was	O
the	O
system	O
utility	O
(	O
IEH	O
)	O
that	O
initialized	O
(	O
INIT	O
)	O
magnetic	O
tape	O
labels	O
(	O
T	O
)	O
.	O
</s>
<s>
Most	O
early	O
users	O
of	O
OS/360	B-Application
were	O
familiar	O
with	O
IBM	O
Assembler	O
Language	O
and	O
would	O
have	O
recognized	O
this	O
at	O
once	O
.	O
</s>
<s>
Example	O
JCL	B-Application
would	O
be	O
:	O
</s>
<s>
To	O
create	O
a	O
Partitioned	O
Data	B-Application
Set	I-Application
:	O
</s>
<s>
IEFBR14	B-Application
consisted	O
initially	O
of	O
a	O
single	O
instruction	O
a	O
"	O
Branch	O
to	O
Register	O
"	O
14	O
.	O
</s>
<s>
The	O
linkage	O
convention	O
for	O
OS/360	B-Application
and	O
its	O
descendants	O
requires	O
that	O
a	O
program	O
be	O
invoked	O
with	O
register	O
14	O
containing	O
the	O
address	O
to	O
return	O
control	O
to	O
when	O
complete	O
,	O
and	O
register	O
15	O
containing	O
the	O
address	O
at	O
which	O
the	O
called	O
program	O
is	O
loaded	O
into	O
memory	O
;	O
at	O
completion	O
,	O
the	O
program	O
loads	O
a	O
return	O
code	O
in	O
register	O
15	O
,	O
and	O
then	O
branches	O
to	O
the	O
address	O
contained	O
in	O
register	O
14	O
.	O
</s>
<s>
But	O
,	O
initially	O
IEFBR14	B-Application
was	O
not	O
coded	O
with	O
these	O
characteristics	O
in	O
mind	O
,	O
as	O
IEFBR14	B-Application
was	O
initially	O
used	O
as	O
a	O
dummy	O
control	O
section	O
,	O
one	O
which	O
simply	O
returned	O
to	O
the	O
caller	O
,	O
not	O
as	O
an	O
executable	O
module	O
.	O
</s>
<s>
Since	O
IEFBR14	B-Application
was	O
always	O
invoked	O
by	O
the	O
functional	O
equivalent	O
of	O
the	O
canonical	O
BALR	O
14	O
,	O
15	O
instruction	O
,	O
the	O
return	O
code	O
in	O
register	O
15	O
was	O
always	O
non-zero	O
.	O
</s>
<s>
Initially	O
,	O
programmers	O
were	O
not	O
using	O
all	O
properties	O
of	O
the	O
Job	B-Application
Control	I-Application
Language	I-Application
,	O
anyway	O
,	O
so	O
an	O
indeterminate	O
return	O
code	O
was	O
not	O
a	O
problem	O
.	O
</s>
<s>
This	O
modification	O
to	O
IEFBR14	B-Application
did	O
not	O
in	O
any	O
way	O
impact	O
its	O
original	O
use	O
as	O
a	O
placeholder	O
.	O
</s>
<s>
This	O
makes	O
perfect	O
sense	O
as	O
the	O
OS/360	B-Application
Initiator	O
initially	O
"	O
attaches	O
"	O
the	O
job-step	O
task	O
using	O
the	O
ATTACH	O
macro-instruction	O
(	O
SVC	B-Operating_System
42	O
)	O
,	O
and	O
"	O
unwinding	O
"	O
the	O
effect	O
of	O
this	O
ATTACH	O
macro	O
(	O
it	O
being	O
a	O
Type	O
2	O
SVC	B-Operating_System
instruction	O
)	O
must	O
be	O
a	O
complementary	O
instruction	O
,	O
namely	O
an	O
EXIT	O
macro	O
(	O
necessarily	O
a	O
Type	O
1	O
SVC	B-Operating_System
instruction	O
,	O
SVC	B-Operating_System
3	O
)	O
.	O
</s>
