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Job Entry Subsystem 2/3
Component of the z/OS operating system

The IBM Job Entry Subsystem (JES) is integral to MVS and z/OS mainframe operating systems, managing batch workloads through two implementations: JES2 and JES3. Since z/OS 3.1 (September 2023), JES3 is no longer included, requiring sites to migrate to JES2 or license JES3plus from Phoenix Software International. JES improves efficiency by dividing job processing into pipelined phases—including input, execution, and output—and by performing spooling to enable simultaneous access to shared storage. JES also uses checkpoint structures to recover job data after failures. Though JES2 and JES3 share core functions, differences affect compatibility; for example, JCL jobs often need minor adjustments to run on the alternate JES due to dataset validation rules unique to each system.

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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 article: Houston Automatic Spooling Priority

HASP was developed by IBM Federal Systems Division contractors at the Johnson Space Center in Houston.23 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.

With the introduction of 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 1973.4 It was many years before the HASP labels were removed from the source code, and the messages issued by JES2 are still prefixed with $HASP. Several JES2 commands continue to support specification of either JES2 or HASP to maintain backwards compatibility.5

ASP

Main article: Attached Support Processor

ASP initially stood for Attached Support Processor,67 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, SVS and 7090 emulation on a 360/65 main processor, but only8 OS/360 and SVS on other S/360 and S/370 models.. ASP was announced in March 1967,9: p.710  and that year was reported to be "running very stably".10

ASP evolved from the design of the 7094/7040 Direct Coupled System, using data channel to data channel communication.11 By attaching an IBM 7040 as a peripheral, processor throughput was more than doubled.

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 selector channels on each host attached to channel-to-channel adapters 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; the 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.

Increased reliability was another advantage to offset the added hardware cost. 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. 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.

In 1973, IBM rewrote ASP and renamed it JES3, supporting MVS only.12

Alternatives

There was also a JES in OS/VS1 that was often referred to as JES1.1314 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.15 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. Far more installations made use of HASP than ASP, and in contemporary z/OS systems, there are many more JES2 installations than JES3. 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.

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. 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 JES3.16 IBM has reassured customers that JES3 will continue to be supported until an end-of-support date is announced.1718 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 JES3.19 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.20

See also

Notes

  • "What is JES?", z/OS concepts (PDF), z/OS Basic Skills Information Center, IBM, pp. 80–81
  • "JES2 Compared to JES3", z/OS concepts (PDF), z/OS Basic Skills Information Center, IBM, pp. 91–92

References

  1. Temel, Meral (September 11, 2023). "z/OS 3.1 Update" (PDF). IBM. Retrieved 2025-01-27. https://www.ibm.com/support/pages/system/files/inline-files/Tech%20Byte%20zOS%203.1%20Update.pdf ↩

  2. IBM (February 26, 1971). The HASP System, February 26, 1971 HASP II (360D-05.1-014) V3M1. Version 3 Modification Level 1. ↩

  3. IBM (September 1976). OS/VS2 HASP II Version 4 User's Guide Program Number 370H-TX-001 VS2 SVS Release 1.7 (PDF). First Edition. GC27-0052-0. http://www.bitsavers.org/pdf/ibm/370/hasp/GC27-0052-0_HASP_II_Version_4_Users_Guide_Sep76.pdf ↩

  4. IBM Corporation (1973). Introduction to OS/VS2 Release 2 (PDF). http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/370/OS_VS2/Release_2_1973/GC28-0661-1_Introduction_to_OS_VS2_Release_2_Mar73.pdf ↩

  5. Jeff Frey (2018-04-16). "JES Deathmatch". Terminal Talk (Podcast). Archived from the original on 2018-04-21. Retrieved 2018-04-20. https://web.archive.org/web/20180421030437/http://terminaltalk.net/PodcastGenerator/?name=episode_44_-_adam_and_katie_-_jes_deathmatch_-_4.16.2018.mp3 ↩

  6. Eventually renamed to Asymmetric Multiprocessing System ↩

  7. IBM. IBM System/360 and System/370 Asymmetric Multiprocessing System: General Information Manual, Program Number 360A-CX-15X. GH20-1173. ↩

  8. However, OS/360 on the 360/85 and SVS on S/370 supported integrated emulators. /wiki/360/85 ↩

  9. Pugh; et al. (1991). IBM's 360 and Early 370 Systems. MIT Press. ISBN 9780262517201. Archived from the original on 2013-02-12. 9780262517201 ↩

  10. "Representative ASP Installation". Computerworld. September 13, 1967. Retrieved February 7, 2013. https://news.google.com/newspapers?id=-qsnAAAAIBAJ&sjid=clQDAAAAIBAJ&pg=3799%2C222384 ↩

  11. Auslander, M.A.; Larkin, D.C.; Scherr, A.L. (September 1981). "The Evolution of the MVS Operating System" (PDF). IBM Journal of Research and Development. 25 (5): 471–482. doi:10.1147/rd.255.0471. S2CID 16424391. Archived from the original (PDF) on 2019-10-09. Retrieved Oct 8, 2019. https://web.archive.org/web/20191009002342/https://pdfs.semanticscholar.org/a8e4/4d068a376c42513a4e10d6a751702710afee.pdf ↩

  12. IBM Corporation (1973). Introduction to OS/VS2 Release 2 (PDF). http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/370/OS_VS2/Release_2_1973/GC28-0661-1_Introduction_to_OS_VS2_Release_2_Mar73.pdf ↩

  13. Baily, J.H.; Howard, J.A.; Szcygieldski, T.J. (1974). "The job entry subsystem of OS/VS1". IBM Systems Journal. 13 (3): 253. doi:10.1147/sj.133.0253. Archived from the original on 2016-03-03. Retrieved 2013-02-11. https://web.archive.org/web/20160303194306/http://domino.research.ibm.com/tchjr/journalindex.nsf/e90fc5d047e64ebf85256bc80066919c/f3b0bdc1a575f74885256bfa00685ab0?OpenDocument ↩

  14. IBM Corporation (1972). OS/Virtual Storage 1 Features Supplement (PDF). http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/370/OS_VS1/GC20-1752-0_OS_VS1_Features_Supplement_Aug72.pdf ↩

  15. "Master Subsystem" (PDF). OS/VS2 System Logic Library Volume 3 - VS2.03.804 - VS2.03.807 - VS2.03.810 (PDF). Systems (First ed.). IBM. July 1976. pp. 3-169 – 3-191. 5Y28-0763-0. Retrieved June 12, 2022. 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 ↩

  16. "IBM z/OS Version 2 Release 3 - Engine for digital transformation". IBM. 2017-07-17. Retrieved 2018-05-04. IBM is affirming that JES2 is the strategic Job Entry Subsystem for z/OS. https://www-01.ibm.com/common/ssi/cgi-bin/ssialias?infotype=AN&subtype=CA&htmlfid=897/ENUS217-246&appname=USN ↩

  17. "Re: IBM to stabilize JES3 (was: IBM to finally drop JES3)". bit.listserv.ibm-main (Mailing list). August 2017. Retrieved 2018-04-20. https://groups.google.com/forum/#!topic/bit.listserv.ibm-main/wfmGCGckxvA ↩

  18. Watson, Cheryl (2017-07-27). "IBM's z14 and z/OS 2.3 Announcements". Watson and Walker. Retrieved 2018-04-17. http://watsonwalker.com/ibms-z14-zos-2-3-announcements/ ↩

  19. "Preview: IBM z/OS Version 2 Release 4". www-01.ibm.com. 2019-02-26. Archived from the original on 2021-01-23. Retrieved 2019-05-03. 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 ↩

  20. International, Phoenix Software (2019-10-02). "Phoenix Software International Announces IBM® JES3 Licensing Agreement". GlobeNewswire News Room (Press release). Retrieved 2019-11-01. http://www.globenewswire.com/news-release/2019/10/02/1924179/0/en/Phoenix-Software-International-Announces-IBM-JES3-Licensing-Agreement.html ↩