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{{about|Input/Output Configuration Program|the IOCP API|Input/output completion port}}
{{Multiple issues|
{{Technical|date=August 2010}}
{{Lead too short|date=December 2021}}
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{{Infobox software
| name = Input/Output Configuration Program
| title = Input/Output Configuration Program
| logo = <!-- [[File:]] -->
| screenshot = <!-- [[File:]] -->
| caption =
| collapsible =
| author = IBM
| developer = IBM
| released = <!-- {{Start date|YYYY|MM|DD}} -->
| discontinued =
| latest release version =
| latest release date = <!-- {{Start date and age|YYYY|MM|DD}} -->
| latest preview version =
| latest preview date = <!-- {{Start date and age|YYYY|MM|DD}} -->
| programming language =
| operating system = stand alone, z/OS, z/VM, z/VSE
| platform = [[IBM System/370#Expanding the address space|IBM System/370-Extended Architecture]]
| size =
| language =
| status =
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| license = Proprietary
| website =
}}
The '''Input/Output Configuration Program''' is a program on [[IBM mainframe]]s.{{When|date=December 2021}}
==History==
In the original [[IBM System/360|S/360]] and [[IBM System/370|S/370]] architectures, each processor had its own set of I/O channels and addressed I/O devices with a 12-bit ''cuu'' address, containing a 4-bit channel number and an 8-bit unit (device) number to be sent on the channel bus in order to select the device; the operating system had to be configured to reflect the processor and ''cuu'' address for each device. The operating system had logic to queue pending I/O on each channel and to handle selection of alternate channels. Initiating an I/O to a channel on a different processor required causing a [[Shoulder tap (software)|shoulder tap]] interrupt on the other processor so that it could initiate the I/O.
Starting with the [[IBM 3081]] and [[IBM 4381]] in [[IBM System/370#Expanding the address space|S/370-Extended Architecture]]<ref name=SA22-708>{{cite manual
| author = IBM
| title = IBM System/370 Extended Architecture Principles of Operation
| id = SA22-7085-1
| version = Second Edition
| date = January 1987}}</ref> mode, IBM changed the I/O architecture to allow the [[Channel Subsystem]] to handle the channel scheduling that the operating system handled in S/370 mode. The new I/O architecture used a 16-bit '''subchannel number''', a 16-bit '''device number''' and an 8-bit '''Channel Path Identifier''' ('''Channel Path Id''' or '''CHPID'''); the [[Channel Subsystem]] was responsible for mapping the '''subchannel number''' to the channel and device numbers, for queuing I/O requests and for selecting from the available paths.
Starting with [[IBM Z#IBM zSeries family|z990]], IBM introduced the concept of a '''Logical Channel Subsystem'''<ref>{{cite manual
| title = IBM IBM eServer zSeries 990 Technical Guide
| id = SG24-6947-01
| date = May 2004
| edition = Second
| section = 4.1 Multiple Logical Channel Subsystem (LCSS)
| section-url = https://www.redbooks.ibm.com/redbooks/pdfs/sg246947.pdf#page=122
| pages = 110–115
| url = https://www.redbooks.ibm.com/redbooks/pdfs/sg246947.pdf
| access-date = May 29, 2023
}}
</ref> ('''LCSS'''); each physical channel (of 1024) has a unique '''Physical Channel Path Identifier''' ('''PCHPID'''), each LCSS has a CHPID to PCHPID mapping and each LPAR is assigned to one LCSS.
Starting with [[System z9]] running [[z/OS]] 1.7, IBM offered the multiple-subchannel set facility, which allowed up to four independent sets of 64 Ki subchannels.<ref>{{cite manual
| title = Multiple Subchannel Sets: An Implementation View
| url = https://www.redbooks.ibm.com/redpapers/pdfs/redp4387.pdf
| publisher = [[IBM]]
| work = Redpapers
| access-date = May 28, 2023
}}
</ref>
The installation was responsible for defining the '''Input/Output Configuration Data Set'''s ('''IOCDS''''s), and the operator could select a specific '''IOCDS''' as part of a [[power on reset]] (POR). '''Input/Output Configuration Program''' ('''IOCP''')<ref name=GC38-0097/><ref name=GC38-0401/><ref name=GC38-0456/> is a program for IBM mainframes that compiles a description of the [[Channel Subsystem]] and [[LPAR]]<ref name=GA22-7123/> configuration, optionally loading it into an [[Input/Output Configuration Data Set]] (IOCDS); it recognizes the syntax of [[MVS Configuration Program]] (MVSCP)<ref name=GC28-1615/> input, and there is no need to maintain separate input files.
The direct use of IOCP and [[MVS Configuration Program|MVSCP]] has been mostly supplanted by Hardware Configuration Definition<ref name=GA22-7525/>(HCD).
==See also==
* [[Channel I/O]]
* [[Computer types]]
* [[History of computing]]
* [[Mainframe computer]]
* [[Timeline of computing]]
==References==
<!--- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes on how to create references using <ref></ref> tags which will then appear here automatically -->
{{Reflist | refs=
<ref name=GA22-7123>{{cite manual
|author = IBM
|title = Enterprise System/9000 Enterprise System/3090: Processor Resource/Systems Manager Planning Guide
|id = GA22-7123-10
|version = Eleventh Edition
|date = August 1993
|url = http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/FRAMESET/DA3A6010/CCONTENTS?DT=19930813120744
}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
<ref name=GA22-7525>
{{cite manual
| author = IBM
| title = z/OS Hardware Configuration Definition Planning
| id = GA22-7525-13
| url=http://publibz.boulder.ibm.com/epubs/pdf/iea2g890.pdf}}
</ref>
<ref name=GC28-1615>{{cite manual
|author = IBM
|title = MVS/ESA: MVS Configuration Program MVS/ESA System Product: JES2 Version 4 JES3 Version 4
|id = GC28-1615-04
|url = http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/BOOKS/IEA4G702/CCONTENTS?DT=19930625065231
|version = Fifth Edition
|date = March 1993
}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
<ref name=GC38-0097>{{cite manual
|author = IBM
|id = GC38-0097-05
|title = Enterprise System/9000 Enterprise System/3090: Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference
|date = February 1993
|version = Sixth Edition
|url = http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/FRAMESET/DA0A4005/CCONTENTS?DT=19930212144028
}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
<ref name=GC38-0401>{{cite manual
| author = IBM
| title = Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference
| id = GC38-0401
| url = http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/BOOKS/da4a4001/CCONTENTS
}}{{Dead link|date=March 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
<ref name=GC38-0456>
{{cite manual
| author = IBM
| title = Stand-Alone IOCP User's Guide
| id = GC38-0456}}
</ref>
}}
== External links ==
*[https://archive.today/20121209075134/http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/BOOKS/da4a4001/CCONTENTS Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference, GC38-0401-00]
*[https://archive.today/20121208184433/http://publibfp.dhe.ibm.com/cgi-bin/bookmgr/BOOKS/iea2g800/CCONTENTS z/OS V1R1.0 HCD Planning, GA22-7525-00]
{{DEFAULTSORT:Input Output Configuration Program}}
[[Category:IBM mainframe operating systems]]
[[Category:IBM mainframe technology]]
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