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→History: typo; different numbered entities; multiple-subchannel set facility |
→History: CHPID is global; cite; z/OS 1.7; PCHPID |
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| 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 had to handle 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 [[System z9]] running [[z/OS]] 1.7, IBM offered the multiple-subchannel set facility, which allowed
| 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> Although some models allowed more than 256 channel paths, each LPAR is limited to 256 CHPIDs and part of the IOCP definition is mapping the CHPIDs for each LPAR to the corresponding Physical Channel Path Identifiers (PCHPIDs).
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.
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