<s>
The	O
Job	B-Application
Entry	I-Application
Subsystem	I-Application
(	O
JES	O
)	O
is	O
a	O
component	O
of	O
IBM	O
's	O
MVS	B-Application
mainframe	O
operating	O
systems	O
that	O
is	O
responsible	O
for	O
managing	O
batch	B-General_Concept
workloads	O
.	O
</s>
<s>
In	O
modern	O
times	O
,	O
there	O
are	O
two	O
distinct	O
implementations	O
of	O
the	O
Job	O
Entry	O
System	O
called	O
JES2	B-Application
and	O
JES3	B-Application
.	O
</s>
<s>
They	O
are	O
designed	O
to	O
provide	O
efficient	O
execution	O
of	O
batch	B-General_Concept
jobs	I-General_Concept
.	O
</s>
<s>
Job	O
processing	O
is	O
divided	O
into	O
several	O
phases	O
to	O
provide	O
parallelism	B-Operating_System
through	O
pipelining	B-General_Concept
.	O
</s>
<s>
These	O
phases	O
include	O
input	O
processing	O
where	O
jobs	O
are	O
read	O
and	O
interpreted	O
,	O
the	O
execution	O
phase	O
where	O
jobs	O
run	O
,	O
and	O
output	O
processing	O
where	O
job	O
output	O
is	O
printed	O
or	O
stored	O
on	O
DASD	B-Application
.	O
</s>
<s>
Jobs	O
that	O
are	O
in	O
the	O
same	O
phase	O
of	O
execution	O
are	O
usually	O
said	O
to	O
reside	O
on	O
a	O
particular	O
queue	B-Device
;	O
for	O
example	O
,	O
jobs	O
that	O
are	O
currently	O
executing	O
are	O
on	O
the	O
execution	O
queue	B-Device
.	O
</s>
<s>
To	O
improve	O
I/O	O
efficiency	O
,	O
JES	O
performs	O
spooling	B-Device
,	O
which	O
provides	O
multiple	O
jobs	O
with	O
simultaneous	O
access	O
to	O
a	O
common	O
storage	O
volume	O
.	O
</s>
<s>
Although	O
JES2	B-Application
and	O
JES3	B-Application
provide	O
the	O
same	O
core	O
functionality	O
,	O
there	O
are	O
certain	O
features	O
that	O
may	O
be	O
present	O
in	O
one	O
JES	O
but	O
not	O
the	O
other	O
.	O
</s>
<s>
JCL	B-Application
is	O
used	O
to	O
define	O
jobs	O
to	O
both	O
JES2	B-Application
and	O
JES3	B-Application
,	O
but	O
small	O
changes	O
usually	O
need	O
to	O
be	O
made	O
to	O
the	O
JCL	B-Application
to	O
get	O
a	O
job	O
written	O
for	O
one	O
JES	O
to	O
run	O
on	O
the	O
other	O
.	O
</s>
<s>
A	O
common	O
issue	O
was	O
that	O
JES3	B-Application
checked	O
that	O
all	O
datasets	O
listed	O
in	O
the	O
JCL	B-Application
existed	O
before	O
execution	O
or	O
that	O
there	O
was	O
a	O
prior	O
step	O
where	O
the	O
dataset	O
was	O
defined	O
as	O
NEW	O
,	O
CATLG	O
.	O
</s>
<s>
JES2	B-Application
did	O
not	O
insist	O
on	O
this	O
,	O
allowing	O
the	O
job	O
to	O
run	O
even	O
though	O
it	O
would	O
fail	O
when	O
the	O
step	O
using	O
it	O
failed	O
to	O
find	O
it	O
.	O
</s>
<s>
OS/360	B-Application
'	O
s	O
batch	B-General_Concept
job	I-General_Concept
processing	O
had	O
limited	O
operational	O
flexibility	O
and	O
performance	O
,	O
which	O
was	O
addressed	O
by	O
two	O
field-developed	O
packages	O
called	O
the	O
Houston	O
Automatic	O
Spooling	B-Device
Priority	O
(	O
HASP	O
)	O
and	O
the	O
Attached	O
Support	O
Processor	O
(	O
ASP	O
)	O
.	O
</s>
<s>
It	O
originally	O
managed	O
job	O
scheduling	O
and	O
print	O
and	O
punch	O
output	O
for	O
a	O
single	O
OS/360	B-Application
computer	O
.	O
</s>
<s>
Multi	O
Access	O
Spool	B-Device
capability	O
was	O
added	O
to	O
let	O
peer	O
computers	O
share	O
a	O
common	O
job	O
queue	B-Device
and	O
print/punch	O
output	O
queues	B-Device
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
System/370	B-Device
in	O
1972	O
,	O
IBM	O
rewrote	O
HASP	O
to	O
become	O
a	O
standard	O
part	O
of	O
the	O
system	O
and	O
renamed	O
it	O
Job	B-Application
Entry	I-Application
Subsystem	I-Application
2	O
.	O
</s>
<s>
JES2	B-Application
was	O
introduced	O
in	O
OS/VS2	B-Application
in	O
Release	O
2	O
,	O
also	O
known	O
as	O
MVS	B-Application
,	O
in	O
1973	O
.	O
</s>
<s>
It	O
was	O
many	O
years	O
before	O
the	O
HASP	O
labels	O
were	O
removed	O
from	O
the	O
source	O
code	O
,	O
and	O
the	O
messages	O
issued	O
by	O
JES2	B-Application
are	O
still	O
prefixed	O
with	O
$HASP	O
.	O
</s>
<s>
Several	O
JES2	B-Application
commands	O
continue	O
to	O
support	O
specification	O
of	O
either	O
JES2	B-Application
or	O
HASP	O
to	O
maintain	O
backwards	B-General_Concept
compatibility	I-General_Concept
.	O
</s>
<s>
It	O
allowed	O
one	O
central	O
system	O
to	O
distribute	O
jobs	O
to	O
multiple	O
connected	O
systems	O
;	O
ASP	O
could	O
run	O
a	O
mixture	O
of	O
OS/360	B-Application
,	O
SVS	B-Application
and	O
7090	O
emulation	O
on	O
a	O
360/65	O
main	O
processor	O
,	O
but	O
only	O
OS/360	B-Application
and	O
SVS	B-Application
on	O
other	O
S/360	O
and	O
S/370	B-Device
models	O
..	O
ASP	O
was	O
announced	O
in	O
March	O
1967	O
,	O
and	O
that	O
year	O
was	O
reported	O
to	O
be	O
"	O
running	O
very	O
stably	O
"	O
.	O
</s>
<s>
ASP	O
evolved	O
from	O
the	O
design	O
of	O
the	O
7094/7040	O
Direct	O
Coupled	O
System	O
,	O
using	O
data	O
channel	O
to	O
data	O
channel	O
communication	O
.	O
</s>
<s>
By	O
attaching	O
an	O
IBM	B-Device
7040	I-Device
as	O
a	O
peripheral	O
,	O
processor	O
throughput	O
was	O
more	O
than	O
doubled	O
.	O
</s>
<s>
The	O
computers	O
were	O
connected	O
through	O
selector	B-Device
channels	I-Device
on	O
each	O
host	O
attached	O
to	O
channel-to-channel	O
adapters	O
in	O
an	O
early	O
form	O
of	O
short	O
distance	O
,	O
point-to-point	O
computer	O
networking	O
.	O
</s>
<s>
ASP	O
required	O
the	O
purchase	O
of	O
an	O
additional	O
computer	O
to	O
manage	O
input	O
and	O
output	O
of	O
the	O
hosts	O
running	O
the	O
job	O
workload	O
,	O
which	O
was	O
economically	O
justified	O
by	O
the	O
high	O
cost	O
of	O
standalone	O
byte-multiplexor	O
channels	O
needed	O
to	O
drive	O
printers	O
and	O
punched	O
card	O
reader	O
devices	O
;	O
the	O
360/50	B-Device
and	O
smaller	O
systems	O
had	O
a	O
built-in	O
byte	O
multiplexor	O
channel	O
,	O
whereas	O
the	O
faster	O
360/65	O
and	O
larger	O
systems	O
required	O
a	O
relatively	O
expensive	O
standalone	O
unit	O
.	O
</s>
<s>
In	O
1973	O
,	O
IBM	O
rewrote	O
ASP	O
and	O
renamed	O
it	O
JES3	B-Application
,	O
supporting	O
MVS	B-Application
only	O
.	O
</s>
<s>
There	O
was	O
also	O
a	O
JES	O
in	O
OS/VS1	B-Application
that	O
was	O
often	O
referred	O
to	O
as	O
JES1	B-Application
.	O
</s>
<s>
Far	O
more	O
installations	O
made	O
use	O
of	O
HASP	O
than	O
ASP	O
,	O
and	O
in	O
contemporary	O
z/OS	O
systems	O
,	O
there	O
are	O
many	O
more	O
JES2	B-Application
installations	O
than	O
JES3	B-Application
.	O
</s>
<s>
Because	O
of	O
their	O
unique	O
history	O
,	O
IBM	O
continues	O
to	O
ship	O
JES2	B-Application
and	O
JES3	B-Application
source	O
code	O
instead	O
of	O
object	B-Language
code	I-Language
,	O
unlike	O
most	O
components	O
of	O
the	O
operating	O
system	O
.	O
</s>
<s>
In	O
2017	O
,	O
IBM	O
released	O
a	O
statement	O
of	O
direction	O
for	O
JES2	B-Application
to	O
be	O
the	O
"	O
strategic	O
"	O
JES	O
,	O
meaning	O
that	O
all	O
future	O
development	O
efforts	O
will	O
be	O
focused	O
on	O
JES2	B-Application
rather	O
than	O
JES3	B-Application
.	O
</s>
<s>
IBM	O
has	O
reassured	O
customers	O
that	O
JES3	B-Application
will	O
continue	O
to	O
be	O
supported	O
until	O
an	O
end-of-support	O
date	O
is	O
announced	O
.	O
</s>
<s>
In	O
February	O
2019	O
,	O
IBM	O
announced	O
that	O
z/OS	O
2.5	O
(	O
expected	O
to	O
be	O
released	O
in	O
2021	O
)	O
will	O
be	O
the	O
last	O
version	O
of	O
z/OS	O
to	O
include	O
JES3	B-Application
.	O
</s>
<s>
In	O
October	O
2019	O
,	O
Phoenix	O
Software	O
International	O
announced	O
that	O
it	O
had	O
licensed	O
the	O
JES3	B-Application
source	O
code	O
from	O
IBM	O
and	O
would	O
be	O
taking	O
over	O
its	O
maintenance	O
and	O
enhancement	O
.	O
</s>
