<s>
Micro	B-Device
Channel	I-Device
architecture	I-Device
,	O
or	O
the	O
Micro	B-Device
Channel	I-Device
bus	B-General_Concept
,	O
is	O
a	O
proprietary	B-Device
16	B-Device
-	I-Device
or	O
32-bit	O
parallel	O
computer	B-General_Concept
bus	I-General_Concept
introduced	O
by	O
IBM	O
in	O
1987	O
which	O
was	O
used	O
on	O
PS/2	B-Device
and	O
other	O
computers	O
until	O
the	O
mid-1990s	O
.	O
</s>
<s>
In	O
IBM	O
products	O
,	O
it	O
superseded	O
the	O
ISA	B-Architecture
bus	I-Architecture
and	O
was	O
itself	O
subsequently	O
superseded	O
by	O
the	O
PCI	B-Protocol
bus	I-Protocol
architecture	O
.	O
</s>
<s>
The	O
development	O
of	O
Micro	B-Device
Channel	I-Device
was	O
driven	O
by	O
both	O
technical	O
and	O
business	O
pressures	O
.	O
</s>
<s>
The	O
IBM	B-Operating_System
AT	I-Operating_System
bus	B-General_Concept
,	O
which	O
later	O
became	O
known	O
as	O
the	O
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
(	O
ISA	B-Architecture
)	O
bus	B-General_Concept
,	O
had	O
a	O
number	O
of	O
technical	O
design	O
limitations	O
,	O
including	O
:	O
</s>
<s>
A	O
slow	O
bus	B-General_Concept
speed	O
.	O
</s>
<s>
Undocumented	O
bus	B-General_Concept
interface	O
standards	O
that	O
varied	O
between	O
systems	O
and	O
manufacturers	O
.	O
</s>
<s>
IBM	O
was	O
already	O
investigating	O
the	O
use	O
of	O
RISC	B-Architecture
processors	I-Architecture
in	O
desktop	O
machines	O
,	O
and	O
could	O
,	O
in	O
theory	O
,	O
save	O
considerable	O
money	O
if	O
a	O
single	O
well-documented	O
bus	B-General_Concept
could	O
be	O
used	O
across	O
their	O
entire	O
computer	O
lineup	O
.	O
</s>
<s>
As	O
patents	O
can	O
take	O
three	O
years	O
or	O
more	O
to	O
be	O
granted	O
,	O
however	O
,	O
only	O
those	O
relating	O
to	O
ISA	B-Architecture
could	O
be	O
licensed	O
when	O
Micro	B-Device
Channel	I-Device
was	O
announced	O
.	O
</s>
<s>
Patents	O
on	O
important	O
Micro	B-Device
Channel	I-Device
features	O
,	O
such	O
as	O
Plug	B-Device
and	I-Device
Play	I-Device
automatic	O
configuration	O
,	O
were	O
not	O
granted	O
to	O
IBM	O
until	O
after	O
PCI	B-Protocol
had	O
replaced	O
Micro	B-Device
Channel	I-Device
in	O
the	O
marketplace	O
.	O
</s>
<s>
The	O
overall	O
reception	O
was	O
tepid	O
and	O
the	O
impact	O
of	O
Micro	B-Device
Channel	I-Device
in	O
the	O
worldwide	O
PC	O
market	O
was	O
minor	O
.	O
</s>
<s>
The	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
was	O
designed	O
by	O
engineer	O
Chet	O
Heath	O
.	O
</s>
<s>
A	O
lot	O
of	O
the	O
Micro	B-Device
Channel	I-Device
cards	O
that	O
were	O
developed	O
used	O
the	O
CHIPS	O
P82C612	O
MCA	O
interface	O
controller	O
;	O
allowing	O
MCA	O
implementations	O
to	O
become	O
a	O
lot	O
easier	O
.	O
</s>
<s>
The	O
Micro	B-Device
Channel	I-Device
was	O
primarily	O
a	O
32-bit	O
bus	B-General_Concept
,	O
but	O
the	O
system	O
also	O
supported	O
a	O
16-bit	B-Device
mode	O
designed	O
to	O
lower	O
the	O
cost	O
of	O
connectors	O
and	O
logic	O
in	O
Intel-based	O
machines	O
like	O
the	O
IBM	B-Device
PS/2	I-Device
.	O
</s>
<s>
The	O
situation	O
was	O
never	O
that	O
simple	O
,	O
however	O
,	O
as	O
both	O
the	O
32-bit	O
and	O
16-bit	B-Device
versions	O
initially	O
had	O
a	O
number	O
of	O
additional	O
optional	O
connectors	O
for	O
memory	O
cards	O
which	O
resulted	O
in	O
a	O
huge	O
number	O
of	O
physically	O
incompatible	O
cards	O
for	O
bus	B-General_Concept
attached	O
memory	O
.	O
</s>
<s>
In	O
time	O
,	O
memory	O
moved	O
to	O
the	O
CPU	O
's	O
local	O
bus	B-General_Concept
,	O
thereby	O
eliminating	O
the	O
problem	O
.	O
</s>
<s>
On	O
the	O
upside	O
,	O
signal	O
quality	O
was	O
greatly	O
improved	O
as	O
Micro	B-Device
Channel	I-Device
added	O
ground	O
and	O
power	O
pins	O
and	O
arranged	O
the	O
pins	O
to	O
minimize	O
interference	O
;	O
a	O
ground	O
or	O
a	O
supply	O
was	O
thereby	O
located	O
within	O
3	O
pins	O
of	O
every	O
signal	O
.	O
</s>
<s>
The	O
advantage	O
of	O
this	O
was	O
that	O
Micro	B-Device
Channel	I-Device
system	O
boards	O
could	O
have	O
a	O
basic	O
VGA	B-Protocol
or	O
MCGA	B-Device
graphics	O
system	O
on	O
board	O
,	O
and	O
higher-level	O
graphics	O
(	O
XGA	B-Device
or	O
other	O
accelerator	O
cards	O
)	O
could	O
then	O
share	O
the	O
same	O
port	O
.	O
</s>
<s>
The	O
add-on	O
cards	O
were	O
then	O
able	O
to	O
be	O
free	O
of	O
'	O
legacy	O
 '	O
VGA	B-Protocol
modes	O
,	O
making	O
use	O
of	O
the	O
on-board	O
graphics	O
system	O
when	O
needed	O
,	O
and	O
allowing	O
a	O
single	O
system	O
board	O
connector	O
for	O
graphics	O
that	O
could	O
be	O
upgraded	O
.	O
</s>
<s>
Micro	B-Device
Channel	I-Device
cards	O
also	O
featured	O
a	O
unique	O
,	O
16-bit	B-Device
software-readable	O
ID	O
,	O
which	O
formed	O
the	O
basis	O
of	O
an	O
early	O
plug	B-Device
and	I-Device
play	I-Device
system	O
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
and/or	O
OS	O
can	O
read	O
IDs	O
,	O
compare	O
against	O
a	O
list	O
of	O
known	O
cards	O
,	O
and	O
perform	O
automatic	O
system	O
configuration	O
to	O
suit	O
.	O
</s>
<s>
This	O
led	O
to	O
boot	O
failures	O
whereby	O
an	O
older	O
BIOS	B-Operating_System
would	O
not	O
recognize	O
a	O
newer	O
card	O
,	O
causing	O
an	O
error	O
at	O
startup	O
.	O
</s>
<s>
In	O
turn	O
,	O
this	O
required	O
IBM	O
to	O
release	O
updated	O
Reference	O
Disks	O
(	O
The	O
CMOS	B-Device
Setup	I-Device
Utility	O
)	O
on	O
a	O
regular	O
basis	O
.	O
</s>
<s>
In	O
this	O
critical	O
area	O
,	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
's	O
biggest	O
advantage	O
was	O
also	O
its	O
greatest	O
disadvantage	O
,	O
and	O
one	O
of	O
the	O
major	O
reasons	O
for	O
its	O
demise	O
.	O
</s>
<s>
The	O
basic	O
data	O
rate	O
of	O
the	O
Micro	B-Device
Channel	I-Device
was	O
increased	O
from	O
ISA	B-Architecture
's	O
8MHz	O
to	O
10MHz	O
.	O
</s>
<s>
This	O
may	O
have	O
been	O
a	O
modest	O
increase	O
in	O
terms	O
of	O
clock	O
rate	O
,	O
but	O
the	O
greater	O
bus	B-General_Concept
width	O
,	O
coupled	O
with	O
a	O
dedicated	O
bus	B-General_Concept
controller	O
that	O
utilized	O
burst	B-Architecture
mode	I-Architecture
transfers	O
,	O
meant	O
that	O
effective	O
throughput	O
was	O
up	O
to	O
five	O
times	O
higher	O
than	O
ISA	B-Architecture
.	O
</s>
<s>
For	O
faster	O
transfers	O
the	O
address	B-Architecture
bus	I-Architecture
could	O
be	O
reused	O
for	O
data	O
,	O
further	O
increasing	O
the	O
effective	O
width	O
of	O
the	O
bus	B-General_Concept
.	O
</s>
<s>
While	O
the	O
10MHz	O
rate	O
allowed	O
40	O
MB/s	O
of	O
throughput	O
at	O
32-bit	O
width	O
,	O
later	O
models	O
of	O
RS/6000	B-Device
machines	O
increased	O
the	O
data	O
rate	O
to	O
20MHz	O
,	O
and	O
the	O
throughput	O
to	O
80	O
MB/s	O
.	O
</s>
<s>
Some	O
higher	O
throughput	O
functions	O
of	O
the	O
Micro	B-Device
Channel	I-Device
bus	B-General_Concept
were	O
available	O
to	O
RS/6000	B-Device
platform	O
only	O
,	O
and	O
were	O
not	O
initially	O
supported	O
on	O
cards	O
operating	O
on	O
an	O
Intel	O
platform	O
.	O
</s>
<s>
With	O
bus	B-Architecture
mastering	I-Architecture
,	O
each	O
card	O
could	O
talk	O
to	O
another	O
directly	O
.	O
</s>
<s>
One	O
potential	O
drawback	O
of	O
multi-master	O
design	O
was	O
the	O
possible	O
collisions	O
when	O
more	O
than	O
one	O
card	O
would	O
try	O
to	O
bus	B-Architecture
master	I-Architecture
,	O
but	O
Micro	B-Device
Channel	I-Device
included	O
an	O
arbitration	O
feature	O
to	O
correct	O
for	O
these	O
situations	O
,	O
and	O
also	O
allowed	O
a	O
master	O
to	O
use	O
a	O
burst-mode	B-Architecture
.	O
</s>
<s>
Micro	B-Device
Channel	I-Device
cards	O
had	O
complete	O
control	O
for	O
up	O
to	O
12	O
milliseconds	O
.	O
</s>
<s>
This	O
was	O
long	O
enough	O
to	O
permit	O
the	O
maximum	O
number	O
of	O
other	O
devices	O
on	O
the	O
bus	B-General_Concept
to	O
buffer	O
inbound	O
data	O
from	O
over-runnable	O
devices	O
like	O
tape	O
and	O
communications	O
.	O
</s>
<s>
Multiple	O
bus-master	O
support	O
and	O
improved	O
arbitration	O
mean	O
that	O
several	O
such	O
devices	O
could	O
coexist	O
and	O
share	O
the	O
system	O
bus	B-General_Concept
.	O
</s>
<s>
Micro	B-Device
Channel	I-Device
bus-master-capable	O
devices	O
can	O
even	O
use	O
the	O
bus	B-General_Concept
to	O
talk	O
directly	O
to	O
each	O
other	O
(	O
peer	O
to	O
peer	O
)	O
at	O
speeds	O
faster	O
than	O
the	O
system	O
CPU	O
,	O
without	O
any	O
other	O
system	O
intervention	O
.	O
</s>
<s>
In	O
theory	O
,	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
systems	O
could	O
be	O
expanded	O
,	O
like	O
mainframes	O
,	O
with	O
only	O
the	O
addition	O
of	O
intelligent	O
masters	O
,	O
without	O
periodic	O
need	O
to	O
upgrade	O
the	O
central	O
processor	O
.	O
</s>
<s>
Rather	O
than	O
a	O
dedicated	O
interrupt	O
line	O
,	O
several	O
lines	O
can	O
be	O
shared	O
to	O
provide	O
more	O
possible	O
interrupts	O
,	O
addressing	O
the	O
ISA-bus	O
interrupt	O
line	O
conflict	O
problems	O
.	O
</s>
<s>
All	O
interrupt	O
request	O
signals	O
were	O
"	O
public	O
"	O
on	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
permitting	O
any	O
card	O
on	O
the	O
bus	B-General_Concept
to	O
function	O
as	O
an	O
I/O	B-Device
processor	I-Device
for	O
direct	O
service	O
of	O
I/O	O
device	O
interrupts	O
.	O
</s>
<s>
ISA	B-Architecture
had	O
limited	O
all	O
such	O
processing	O
to	O
just	O
the	O
system	O
's	O
CPU	O
.	O
</s>
<s>
Likewise	O
,	O
bus	B-Architecture
master	I-Architecture
request	O
and	O
grant	O
signals	O
were	O
public	O
,	O
such	O
that	O
bus	B-General_Concept
attached	O
devices	O
could	O
monitor	O
latency	O
to	O
control	O
internal	O
buffering	O
for	O
I/O	B-Device
processors	I-Device
.	O
</s>
<s>
These	O
features	O
were	O
not	O
adopted	O
for	O
PCI	B-Protocol
,	O
requiring	O
all	O
I/O	O
support	O
to	O
come	O
uniquely	O
from	O
the	O
system	O
board	O
processor	O
.	O
</s>
<s>
The	O
final	O
major	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
improvement	O
was	O
POS	O
,	O
the	O
Programmable	O
Option	O
Select	O
,	O
which	O
allowed	O
all	O
setup	O
to	O
take	O
place	O
in	O
software	O
.	O
</s>
<s>
This	O
feature	O
is	O
taken	O
for	O
granted	O
now	O
,	O
but	O
at	O
the	O
time	O
setup	O
was	O
a	O
huge	O
chore	O
for	O
ISA	B-Architecture
systems	O
.	O
</s>
<s>
(	O
This	O
type	O
of	O
software-configuration	O
system	O
is	O
known	O
as	O
plug	B-Device
and	I-Device
play	I-Device
today	O
.	O
)	O
</s>
<s>
The	O
feature	O
did	O
not	O
really	O
live	O
up	O
to	O
its	O
promise	O
;	O
the	O
automatic	O
configuration	O
was	O
fine	O
when	O
it	O
worked	O
,	O
but	O
it	O
frequently	O
did	O
not	O
-	O
resulting	O
in	O
an	O
unbootable	O
computer	O
-	O
and	O
resolving	O
the	O
problem	O
by	O
manual	O
intervention	O
was	O
much	O
more	O
difficult	O
than	O
configuring	O
an	O
ISA	B-Architecture
system	O
,	O
not	O
least	O
because	O
the	O
documentation	O
for	O
the	O
MCA	O
device	O
would	O
tend	O
to	O
assume	O
that	O
the	O
automatic	O
configuration	O
would	O
work	O
and	O
so	O
did	O
not	O
provide	O
the	O
necessary	O
information	O
to	O
set	O
it	O
up	O
by	O
hand	O
,	O
unlike	O
ISA	B-Architecture
device	O
documentation	O
which	O
by	O
necessity	O
provided	O
full	O
details	O
(	O
however	O
having	O
to	O
physically	O
remove	O
and	O
check	O
all	O
IRQ	O
settings	O
,	O
then	O
find	O
and	O
set	O
the	O
new	O
IRQ	O
for	O
a	O
new	O
device	O
—	O
if	O
a	O
suitable	O
one	O
was	O
available	O
—	O
for	O
ISA	B-Architecture
was	O
no	O
fun	O
at	O
all	O
,	O
and	O
beyond	O
many	O
users	O
...	O
it	O
is	O
obvious	O
why	O
the	O
attempt	O
was	O
made	O
to	O
move	O
to	O
software	O
arbitrated	O
configuration	O
,	O
and	O
why	O
this	O
was	O
to	O
later	O
succeed	O
in	O
the	O
form	O
of	O
PnP	B-Device
.	O
)	O
</s>
<s>
Micro	B-Device
Channel	I-Device
architecture	I-Device
was	O
first	O
introduced	O
at	O
the	O
launch	O
of	O
the	O
PS/2	B-Device
range	O
in	O
1987	O
,	O
with	O
three	O
out	O
of	O
four	O
of	O
the	O
new	O
machines	O
featuring	O
it	O
.	O
</s>
<s>
Its	O
use	O
in	O
IBM	O
spread	O
to	O
the	O
RS/6000	B-Device
,	O
AS/400	B-Device
,	O
and	O
eventually	O
to	O
the	O
IBM	B-Device
9370	I-Device
systems	O
-	O
smallest	O
members	O
of	O
the	O
System/370	B-Device
range	O
.	O
</s>
<s>
NCR	O
Corporation	O
adopted	O
Micro	B-Device
Channel	I-Device
comprehensively	O
-	O
they	O
designed	O
and	O
built	O
high-performance	O
personal	O
computer	O
,	O
workstation	O
and	O
server	O
platforms	O
supporting	O
it	O
,	O
including	O
their	O
own	O
Micro	B-Device
Channel	I-Device
architecture-based	O
logic	O
componentry	O
,	O
including	O
SCSI	B-Architecture
,	O
graphics	O
,	O
networking	O
,	O
and	O
audio	O
.	O
</s>
<s>
Despite	O
the	O
fact	O
that	O
MCA	O
was	O
a	O
huge	O
technical	O
improvement	O
over	O
ISA	B-Architecture
,	O
it	O
soon	O
became	O
clear	O
that	O
its	O
introduction	O
and	O
marketing	O
by	O
IBM	O
was	O
poorly	O
handled	O
.	O
</s>
<s>
IBM	O
had	O
strong	O
patents	O
on	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
system	O
features	O
,	O
and	O
required	O
Micro	B-Device
Channel	I-Device
system	O
manufacturers	O
to	O
pay	O
a	O
licence	O
fee	O
-	O
and	O
actively	O
pursued	O
patents	O
to	O
block	O
third	O
parties	O
from	O
selling	O
unlicensed	O
implementations	O
of	O
it	O
.	O
</s>
<s>
The	O
PC	O
clone	O
market	O
did	O
not	O
want	O
to	O
pay	O
royalties	O
to	O
IBM	O
in	O
order	O
to	O
use	O
this	O
new	O
technology	O
,	O
and	O
stayed	O
largely	O
with	O
the	O
16-bit	B-Device
AT	B-Architecture
bus	I-Architecture
,	O
(	O
embraced	O
and	O
renamed	O
as	O
ISA	B-Architecture
to	O
avoid	O
IBM	O
's	O
"	O
AT	O
"	O
trademark	O
)	O
and	O
manual	O
configuration	O
,	O
although	O
the	O
VESA	O
Local	O
Bus	B-General_Concept
(	O
VLB	O
)	O
was	O
briefly	O
popular	O
for	O
Intel	B-General_Concept
'	I-General_Concept
486	I-General_Concept
machines	O
.	O
</s>
<s>
For	O
servers	O
the	O
technical	O
limitations	O
of	O
the	O
old	O
ISA	B-Architecture
were	O
too	O
great	O
,	O
and	O
,	O
in	O
late	O
1988	O
,	O
the	O
"	O
Gang	B-Device
of	I-Device
Nine	I-Device
"	O
,	O
led	O
by	O
Compaq	O
,	O
announced	O
a	O
rival	O
high-performance	O
bus	B-General_Concept
-	O
Extended	B-Device
Industry	I-Device
Standard	I-Device
Architecture	I-Device
(	O
EISA	O
)	O
.	O
</s>
<s>
This	O
offered	O
similar	O
performance	O
benefits	O
to	O
Micro	B-Device
Channel	I-Device
,	O
but	O
with	O
the	O
twin	O
advantage	O
of	O
being	O
able	O
to	O
accept	O
older	O
ISA	B-Architecture
boards	O
and	O
being	O
free	O
from	O
IBM	O
's	O
control	O
.	O
</s>
<s>
For	O
several	O
years	O
EISA	O
and	O
Micro	B-Device
Channel	I-Device
battled	O
it	O
out	O
in	O
the	O
server	O
arena	O
,	O
but	O
,	O
in	O
1996	O
,	O
IBM	O
effectively	O
conceded	O
defeat	O
,	O
when	O
they	O
themselves	O
produced	O
some	O
EISA-bus	O
servers	O
.	O
</s>
<s>
In	O
2001	O
IBM	O
executive	O
Robert	O
Moffat	O
said	O
that	O
of	O
the	O
company	O
's	O
mistakes	O
in	O
the	O
PC	O
market	O
,	O
"	O
the	O
most	O
obvious	O
one	O
is	O
Micro	B-Device
Channel	I-Device
"	O
.	O
</s>
<s>
Within	O
a	O
few	O
years	O
of	O
its	O
arrival	O
in	O
1992	O
,	O
PCI	B-Protocol
had	O
largely	O
superseded	O
Micro	B-Device
Channel	I-Device
,	O
EISA	O
,	O
and	O
VLB	O
.	O
</s>
<s>
In	O
response	O
to	O
the	O
rise	O
of	O
EISA	O
,	O
IBM	O
and	O
thirteen	O
Micro	B-Device
Channel	I-Device
card	O
and	O
peripheral	O
manufacturers	O
formed	O
the	O
Micro	B-Device
Channel	I-Device
Developers	O
Association	O
.	O
</s>
<s>
This	O
was	O
a	O
consortium	O
that	O
sought	O
to	O
consider	O
and	O
prioritize	O
steps	O
in	O
the	O
maturation	O
of	O
Micro	B-Device
Channel	I-Device
,	O
as	O
well	O
as	O
to	O
explore	O
better	O
approaches	O
to	O
disseminating	O
technical	O
information	O
about	O
Micro	B-Device
Channel	I-Device
to	O
third	O
parties	O
.	O
</s>
<s>
A	O
number	O
of	O
non-PS/2	O
computers	O
were	O
manufactured	O
between	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
.	O
</s>
<s>
Such	O
third-party	O
computers	O
were	O
also	O
referred	O
to	O
as	O
PS/2	B-Device
clones	O
or	O
MCA	O
clones	O
.	O
</s>
<s>
The	O
first	O
third-party	O
Micro	B-Device
Channel	I-Device
–	O
based	O
computer	O
was	O
Tandy	O
Corporation	O
's	O
5000	O
MC	O
in	O
1988	O
.	O
</s>
<s>
Despite	O
expensive	O
research	O
and	O
development	O
costs	O
on	O
the	O
part	O
of	O
third-party	O
manufacturers	O
of	O
Micro	B-Device
Channel	I-Device
computers	O
—	O
in	O
part	O
due	O
to	O
the	O
expensive	O
licensing	O
fees	O
incurred	O
by	O
IBM	O
in	O
order	O
to	O
allow	O
legal	O
use	O
of	O
the	O
Micro	B-Device
Channel	I-Device
technology	O
—	O
by	O
1990	O
most	O
MCA	O
clones	O
were	O
not	O
fully	O
compatible	O
with	O
the	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
or	O
expansion	O
cards	O
based	O
on	O
Micro	B-Device
Channel	I-Device
.	O
</s>
<s>
By	O
the	O
time	O
IBM	O
was	O
winding	O
down	O
the	O
PS/2	B-Device
line	O
of	O
personal	O
computers	O
(	O
which	O
in	O
1987	O
acted	O
as	O
the	O
means	O
of	O
introducing	O
Micro	B-Device
Channel	I-Device
to	O
the	O
general	O
public	O
)	O
in	O
1992	O
,	O
NCR	O
Corporation	O
remained	O
the	O
one	O
of	O
a	O
few	O
remaining	O
committed	O
vendors	O
of	O
MCA	O
clones	O
.	O
</s>
<s>
Expansion	O
cards	O
for	O
the	O
Micro	B-Device
Channel	I-Device
bus	B-General_Concept
typically	O
targeted	O
high-end	O
graphic	O
workstation	O
or	O
server	O
requirements	O
,	O
with	O
SCSI	B-Architecture
,	O
Token	B-Device
Ring	I-Device
,	O
Ethernet	O
,	O
IBM	B-Device
5250	I-Device
and	O
IBM	B-Operating_System
3270	I-Operating_System
connections	O
.	O
</s>
