Editing Job Entry Subsystem 2/3 (section)

=== 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 />