Editing Job Entry Subsystem 2/3 (section)

== History ==
=== Precursors ===
[[OS/360]]'s batch job processing had limited operational flexibility and performance, which was addressed by two field-developed packages called the ''Houston Automatic Spooling Priority'' (''HASP'') and the ''Attached Support Processor'' (''ASP'').

==== HASP ====
{{Main|Houston Automatic Spooling Priority}}
HASP was developed by IBM Federal Systems Division contractors at the [[Johnson Space Center]] in [[Houston]].<ref name=HASPIIV3M1/><ref name=GC27-0052/> It originally managed job scheduling and print and punch output for a single OS/360 computer. ''Multi Access Spool'' capability was added to let peer computers share a common job queue and print/punch output queues.{{citation needed|date=May 2018}}

With the introduction of [[IBM System/370|System/370]] in 1972, IBM rewrote HASP to become a standard part of the system and renamed it ''Job Entry Subsystem 2''. JES2 was introduced in OS/VS2 in Release 2, also known as [[MVS]], in 1973.<ref name=VS2Intro/> It was many years before the HASP labels were removed from the source code, and the messages issued by JES2 are still prefixed with <code>$HASP</code>.  Several JES2 commands continue to support specification of either <code>JES2</code> or <code>HASP</code> to maintain [[backwards compatibility]].<ref name=jes-deathmatch-2018-april/>

==== ASP ====
{{main|Attached Support Processor}}{{More citations needed section|date=January 2022}}
ASP initially stood for ''Attached Support Processor'',{{efn|Eventually renamed to ''Asymmetric Multiprocessing System''}}<ref name=GH20-1173/> and was developed to provide efficient use of multiple systems with a shared workload. It allowed one central system to distribute jobs to multiple connected systems; ASP could run a mixture of [[OS/360]], [[OS/VS2 (SVS)|SVS]] and 7090 emulation on a 360/65 main processor, but only{{efn|However, OS/360 on the [[360/85]] and SVS on S/370 supported integrated emulators.}} OS/360 and SVS on other S/360 and S/370 models.. ASP was announced in March 1967,<ref name=pugh-1991/>{{rp|p.710}} and that year was reported to be "running very stably".<ref name=computer-world-1967/>

ASP evolved from the design of the [[IBM 7094|7094]]/[[IBM 7044|7040]] Direct Coupled System, using data channel to data channel communication.<ref>{{cite journal |last1=Auslander |first1=M.A. |last2=Larkin |first2=D.C. |last3=Scherr |first3=A.L. |title=The Evolution of the MVS Operating System |journal=IBM Journal of Research and Development |date=September 1981 |volume=25 |issue=5 |pages=471–482 |url=https://pdfs.semanticscholar.org/a8e4/4d068a376c42513a4e10d6a751702710afee.pdf |archive-url=https://web.archive.org/web/20191009002342/https://pdfs.semanticscholar.org/a8e4/4d068a376c42513a4e10d6a751702710afee.pdf |url-status=dead |archive-date=2019-10-09 |accessdate=Oct 8, 2019 |doi=10.1147/rd.255.0471|s2cid=16424391 }}</ref> By attaching an IBM 7040 as a peripheral, processor throughput was more than doubled.{{citation needed|date=May 2018}}

In a typical ASP configuration, a small mainframe such as a 360/40 called the ''support'' system controlled one or more 360/65 or larger processors called ''main'' systems. The computers were connected through [[Channel I/O|selector channels]] on each host attached to [[channel-to-channel adapter]]s in an early form of short distance, point-to-point computer networking.

ASP required the purchase of an additional computer to manage input and output of the hosts running the job workload, which was economically justified by the high cost of standalone byte-multiplexor channels needed to drive printers and punched card reader devices;{{citation needed|date=May 2018}} the [[IBM System/360 Model 50|360/50]] and smaller systems had a built-in byte multiplexor channel, whereas the faster 360/65 and larger systems required a relatively expensive standalone unit. Using ASP made it possible to avoid the cost of the byte multiplexor channel, and offloading the job scheduling, print, and card handling also offloaded those functions from the larger machines.{{citation needed|date=May 2018}}

Increased reliability was another advantage to offset the added hardware cost.{{citation needed|date=May 2018}} One or more ''main'' systems could fail or be taken offline for maintenance without taking down the whole complex.

ASP was primarily targeted at large government agencies and defense contractors that might have as many as six 360/65s all being scheduled and managed by a separate ASP machine.{{citation needed|date=May 2018}} An uncommon variant, ''local ASP'' (''LASP''), was a single large machine with the ASP functions running on the same machine.

In the 1970s, a notable installation of ASP was at Princeton University controlling an IBM 360/91 mainframe.{{citation needed|date=May 2018}}

In 1973, IBM rewrote ASP and renamed it JES3, supporting MVS only.<ref name=VS2Intro />

=== Alternatives ===
There was also a JES in [[OS/VS1]] that was often referred to as [[Job Entry Subsystem 1|JES1]].<ref name=ibm-systems-journal-13-3-253/><ref name=gc20-1752-0/> In addition, the ''master'' (''MSTR'') subsystem, which is built into MVS, can start jobs that run outside of the control of the primary  JES, including the ''Master Scheduler'' and the primary JES itself.<ref>{{cite manual
 | title       = OS/VS2 System Logic Library Volume 3 - VS2.03.804 - VS2.03.807 - VS2.03.810
 | id          = 5Y28-0763-0
 | date        = July 1976
 | edition     = First
 | section     = Master Subsystem
 | section-url = http://bitsavers.org/pdf/ibm/370/OS_VS2/PLM/SY28-0763-0_OS_VS2_System_Logic_Library_Vol_3_Rel_3.7_Jul76.pdf#page=343
 | pages       = 3-169-3-191
 | url         = http://bitsavers.org/pdf/ibm/370/OS_VS2/PLM/SY28-0763-0_OS_VS2_System_Logic_Library_Vol_3_Rel_3.7_Jul76.pdf
 | access-date = June 12, 2022
 | publisher   = [[IBM]]
 | series      = Systems
 }}
</ref> Originally the JCL for the Master subsystem was in an IBM provided load modules, but in current versions of MVS through z/OS, it can be provided as a member of the system parameter library (PARMLIB).

=== Customization ===
Source code was provided to IBM customers for both ASP and HASP, and many customers made substantial enhancements to these programs, some of which were incorporated into the official product.{{citation needed|date=May 2018}}  Far more installations made use of HASP than ASP, and in contemporary z/OS systems, there are many more JES2 installations than JES3.{{citation needed|date=May 2018}}  Because of their unique history, IBM continues to ship JES2 and JES3 [[source code]] instead of [[object code]], unlike most components of the operating system.{{citation needed|date=May 2018}}

To improve maintainability and serviceability of user-written enhancements, JES provides a set of exit points that pass control from the JES to user programs at key points of processing.{{citation needed|date=May 2018}}  These extensions can provide custom functionality such as special commands, custom print page headings, and non-standard job processing.

=== Current development ===
In 2017, IBM released a statement of direction for JES2 to be the "strategic" JES, meaning that all future development efforts will be focused on JES2 rather than JES3.<ref name=ibm-announcement-letter-2017/> IBM has reassured customers that JES3 will continue to be supported until an end-of-support date is announced.<ref name=listserv-ibm-main-august-2017/><ref name=watsonwalker-july-2017/> In February 2019, IBM announced that z/OS 2.5 (expected to be released in 2021) will be the last version of z/OS to include JES3.<ref>{{Cite web|url=https://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/2/877/ENUSZP19-0012/index.html&request_locale=en#availx|title=Preview: IBM z/OS Version 2 Release 4|date=2019-02-26|website=www-01.ibm.com|language=en-US|access-date=2019-05-03|archive-url=https://web.archive.org/web/20210123212905/https://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/2/877/ENUSZP19-0012/index.html&request_locale=en#availx|archive-date=2021-01-23}}</ref> In October 2019, Phoenix Software International announced that it had licensed the JES3 source code from IBM and would be taking over its maintenance and enhancement.<ref>{{Cite press release|url=http://www.globenewswire.com/news-release/2019/10/02/1924179/0/en/Phoenix-Software-International-Announces-IBM-JES3-Licensing-Agreement.html|title=Phoenix Software International Announces IBM® JES3 Licensing Agreement|last=International|first=Phoenix Software|date=2019-10-02|website=GlobeNewswire News Room|access-date=2019-11-01}}</ref>