Input/Output Configuration Program
Original author(s)IBM
Developer(s)IBM
Operating systemstand alone, z/OS, z/VM, z/VSE
PlatformIBM System/370-Extended Architecture
LicenseProprietary

The Input/Output Configuration Program is a program on IBM mainframes.

History

In the original S/360 and 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 interrupt on the other processor so that it could initiate the I/O.

Starting with the IBM 3081 and IBM 4381 in S/370-Extended Architecture[1] 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 z990, IBM introduced the concept of a Logical Channel Subsystem[2] (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.[3]

The installation was responsible for defining the Input/Output Configuration Data Sets (IOCDS's), and the operator could select a specific IOCDS as part of a power on reset (POR). Input/Output Configuration Program (IOCP)[4][5][6] is a program for IBM mainframes that compiles a description of the Channel Subsystem and LPAR[7] configuration, optionally loading it into an Input/Output Configuration Data Set (IOCDS); it recognizes the syntax of MVS Configuration Program (MVSCP)[8] input, and there is no need to maintain separate input files.

The direct use of IOCP and MVSCP has been mostly supplanted by Hardware Configuration Definition[9](HCD).

See also

References

  1. ↑ IBM (January 1987). IBM System/370 Extended Architecture Principles of Operation. Second Edition. SA22-7085-1.
  2. ↑ "4.1 Multiple Logical Channel Subsystem (LCSS)" (PDF). IBM IBM eServer zSeries 990 Technical Guide (PDF) (Second ed.). May 2004. pp. 110–115. SG24-6947-01. Retrieved May 29, 2023.
  3. ↑ Multiple Subchannel Sets: An Implementation View (PDF). IBM. Retrieved May 28, 2023. {{cite book}}: |work= ignored (help)
  4. ↑ IBM (February 1993). Enterprise System/9000 Enterprise System/3090: Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference. Sixth Edition. GC38-0097-05.
  5. ↑ IBM. Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference. GC38-0401.
  6. ↑ IBM. Stand-Alone IOCP User's Guide. GC38-0456.
  7. ↑ IBM (August 1993). Enterprise System/9000 Enterprise System/3090: Processor Resource/Systems Manager Planning Guide. Eleventh Edition. GA22-7123-10.
  8. ↑ IBM (March 1993). MVS/ESA: MVS Configuration Program MVS/ESA System Product: JES2 Version 4 JES3 Version 4. Fifth Edition. GC28-1615-04.
  9. ↑ IBM. z/OS Hardware Configuration Definition Planning (PDF). GA22-7525-13.
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