<s>
is	O
a	O
device	O
that	O
connects	O
two	O
input/output	B-General_Concept
channels	B-Device
on	O
(	O
usually	O
)	O
two	O
separate	O
computer	O
systems	O
.	O
</s>
<s>
The	O
adapter	O
allows	O
one	O
computer	O
system	O
to	O
be	O
treated	O
as	O
an	O
input/output	B-General_Concept
device	I-General_Concept
by	O
another	O
.	O
</s>
<s>
Virtual	O
channel-to-channel	O
adapters	O
(	O
VCTCA	O
)	O
are	O
often	O
used	O
to	O
communicate	O
between	O
two	O
virtual	B-Architecture
machines	I-Architecture
in	O
the	O
z/VM	B-Application
operating	O
system	O
.	O
</s>
<s>
The	O
Virtual	B-Application
Machine	I-Application
Communication	I-Application
Facility	I-Application
(	O
VMCF	B-Application
)	O
,	O
and	O
later	O
Inter	B-Application
User	I-Application
Communication	I-Application
Vehicle	I-Application
(	O
IUCV	B-Application
)	O
are	O
now	O
often	O
used	O
in	O
place	O
of	O
VCTCAs	O
because	O
they	O
provide	O
a	O
simpler	O
interface	O
and	O
improved	O
performance	O
.	O
</s>
