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{{about|Input/Output Configuration Program|the IOCP API|Input/output completion port}}
{{Technical|date=August 2010}}
{{Infobox software
| name = Input/Output Configuration Program
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The '''Input/Output Configuration Program''' is a program on [[IBM mainframe]]s.{{When}}
==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.
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