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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 mode, IBM changed the I/O architecture to allow the [1 ] 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 Channel Path Id ( CHPID); the Channel Subsystem was responsible for mapping the CHPID to the channel and device numbers, for queuing I/O requests and for selecting from the available paths. 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) [2 ] [3 ] is a program for IBM mainframes that compiles a description of the [4 ] Channel Subsystem and LPAR configuration, optionally loading it into an [5 ] Input/Output Configuration Data Set (IOCDS); it recognizes the syntax of MVS Configuration Program (MVSCP) input, and there is no need to maintain separate input files. [6 ]
The direct use of IOCP and
MVSCP has been mostly supplanted by Hardware Configuration Definition (HCD). [7 ]
References [ edit ]
^ IBM (January 1987), IBM System/370 Extended Architecture Principles of Operation, Second Edition, SA22-7085-1.
^ IBM (February 1993), , Sixth Edition, GC38-0097-05. Enterprise System/9000 Enterprise System/3090: Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference
^ IBM, , GC38-0401. Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference
^ IBM, Stand-Alone IOCP User's Guide, GC38-0456.
^ IBM (August 1993), , Eleventh Edition, GA22-7123-10. Enterprise System/9000 Enterprise System/3090: Processor Resource/Systems Manager Planning Guide
^ IBM (March 1993), , Fifth Edition, GC28-1615-04. MVS/ESA: MVS Configuration Program MVS/ESA System Product: JES2 Version 4 JES3 Version 4
^ IBM, , GA22-7525-13. z/OS Hardware Configuration Definition Planning
External links [ edit ]