<s>
The	O
Input/Output	B-Application
Configuration	I-Application
Program	I-Application
is	O
a	O
program	O
on	O
IBM	B-Device
mainframes	I-Device
.	O
</s>
<s>
In	O
the	O
original	O
S/360	B-Application
and	O
S/370	B-Device
architectures	O
,	O
each	O
processor	O
had	O
its	O
own	O
set	O
of	O
I/O	B-Device
channels	I-Device
and	O
addressed	O
I/O	O
devices	O
with	O
a	O
12-bit	O
cuu	O
address	O
,	O
containing	O
a	O
4-bit	O
channel	O
number	O
and	O
an	O
8-bit	O
unit	O
(	O
device	O
)	O
number	O
to	O
be	O
sent	O
on	O
the	O
channel	O
bus	O
in	O
order	O
to	O
select	O
the	O
device	O
;	O
the	O
operating	O
system	O
had	O
to	O
be	O
configured	O
to	O
reflect	O
the	O
processor	O
and	O
cuu	O
address	O
for	O
each	O
device	O
.	O
</s>
<s>
Initiating	O
an	O
I/O	O
to	O
a	O
channel	O
on	O
a	O
different	O
processor	O
required	O
causing	O
a	O
shoulder	B-Device
tap	I-Device
interrupt	O
on	O
the	O
other	O
processor	O
so	O
that	O
it	O
could	O
initiate	O
the	O
I/O	O
.	O
</s>
<s>
Starting	O
with	O
the	O
IBM	B-Device
3081	I-Device
and	O
IBM	O
4381	O
in	O
S/370	B-Device
-Extended	O
Architecture	O
mode	O
,	O
IBM	O
changed	O
the	O
I/O	O
architecture	O
to	O
allow	O
the	O
Channel	O
Subsystem	O
to	O
handle	O
the	O
channel	O
scheduling	O
that	O
the	O
operating	O
system	O
had	O
to	O
handle	O
in	O
S/370	B-Device
mode	O
.	O
</s>
<s>
The	O
installation	O
was	O
responsible	O
for	O
defining	O
the	O
Input/Output	O
Configuration	O
Data	O
Sets	O
(	O
IOCDS	B-Application
's	O
)	O
,	O
and	O
the	O
operator	O
could	O
select	O
a	O
specific	O
IOCDS	B-Application
as	O
part	O
of	O
a	O
power	B-Application
on	I-Application
reset	I-Application
(	O
POR	O
)	O
.	O
</s>
<s>
Input/Output	B-Application
Configuration	I-Application
Program	I-Application
(	O
IOCP	O
)	O
is	O
a	O
program	O
for	O
IBM	B-Device
mainframes	I-Device
that	O
compiles	O
a	O
description	O
of	O
the	O
Channel	O
Subsystem	O
and	O
LPAR	B-Device
configuration	O
,	O
optionally	O
loading	O
it	O
into	O
an	O
Input/Output	O
Configuration	O
Data	O
Set	O
(	O
IOCDS	B-Application
)	O
;	O
it	O
recognizes	O
the	O
syntax	O
of	O
MVS	O
Configuration	O
Program	O
(	O
MVSCP	O
)	O
input	O
,	O
and	O
there	O
is	O
no	O
need	O
to	O
maintain	O
separate	O
input	O
files	O
.	O
</s>
