<s>
The	O
Personal	O
System/2	O
or	O
PS/2	O
is	O
IBM	O
's	O
second	O
generation	O
of	O
personal	B-Device
computers	I-Device
.	O
</s>
<s>
Released	O
in	O
1987	O
,	O
it	O
officially	O
replaced	O
the	O
IBM	B-Device
PC	I-Device
,	O
XT	B-Device
,	O
AT	B-Device
,	O
and	O
PC	B-Device
Convertible	I-Device
in	O
IBM	O
's	O
lineup	O
.	O
</s>
<s>
Many	O
of	O
the	O
PS/2	O
'	O
s	O
innovations	O
,	O
such	O
as	O
the	O
16550	B-Device
UART	I-Device
(	O
serial	O
port	O
)	O
,	O
1440	O
KB	O
3.5-inch	O
floppy	B-Device
disk	I-Device
format	O
,	O
72-pin	O
SIMMs	B-General_Concept
,	O
the	O
PS/2	O
port	O
,	O
and	O
the	O
VGA	B-Protocol
video	O
standard	O
,	O
went	O
on	O
to	O
become	O
standards	O
in	O
the	O
broader	O
PC	O
market	O
.	O
</s>
<s>
The	O
PS/2	O
line	O
was	O
created	O
by	O
IBM	O
partly	O
in	O
an	O
attempt	O
to	O
recapture	O
control	O
of	O
the	O
PC	O
market	O
by	O
introducing	O
the	O
advanced	O
yet	O
proprietary	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
(	O
MCA	O
)	O
on	O
higher-end	O
models	O
.	O
</s>
<s>
Most	O
major	O
PC	O
manufacturers	O
balked	O
at	B-Device
IBM	O
's	O
licensing	O
terms	O
for	O
MCA-compatible	O
hardware	O
,	O
particularly	O
the	O
per-machine	O
royalties	O
.	O
</s>
<s>
The	O
OS/2	B-Application
operating	O
system	O
was	O
announced	O
at	B-Device
the	O
same	O
time	O
as	O
the	O
PS/2	O
line	O
and	O
was	O
intended	O
to	O
be	O
the	O
primary	O
operating	O
system	O
for	O
models	O
with	O
Intel	B-General_Concept
80286	I-General_Concept
or	O
later	O
processors	O
.	O
</s>
<s>
However	O
,	O
at	B-Device
the	O
time	O
of	O
the	O
first	O
shipments	O
,	O
only	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
3.3	O
was	O
available	O
.	O
</s>
<s>
OS/2	B-Application
1.0	O
(	O
text-mode	O
only	O
)	O
and	O
Microsoft	O
's	O
Windows	B-Application
2.0	I-Application
became	O
available	O
several	O
months	O
later	O
.	O
</s>
<s>
IBM	O
also	O
released	O
AIX	B-Application
PS/2	O
,	O
a	O
UNIX	B-Application
operating	I-Application
system	I-Application
for	O
PS/2	O
models	O
with	O
Intel	B-General_Concept
386	I-General_Concept
or	O
later	O
processors	O
.	O
</s>
<s>
IBM	O
's	O
PS/2	O
was	O
designed	O
to	O
remain	O
software	O
compatible	O
with	O
their	O
PC/AT/XT	O
line	O
of	O
computers	O
upon	O
which	O
the	O
large	O
PC	O
clone	O
market	O
was	O
built	O
,	O
but	O
the	O
hardware	O
was	O
quite	O
different	O
.	O
</s>
<s>
PS/2	O
had	O
two	O
BIOSes	O
:	O
one	O
named	O
ABIOS	B-Operating_System
(	O
Advanced	B-Operating_System
BIOS	I-Operating_System
)	O
which	O
provided	O
a	O
new	O
protected	B-Application
mode	I-Application
interface	O
and	O
was	O
used	O
by	O
OS/2	B-Application
,	O
and	O
CBIOS	B-Operating_System
(	O
Compatible	O
BIOS	B-Operating_System
)	O
which	O
was	O
included	O
to	O
be	O
software	O
compatible	O
with	O
the	O
PC/AT/XT	O
.	O
</s>
<s>
CBIOS	B-Operating_System
was	O
so	O
compatible	O
that	O
it	O
even	O
included	O
Cassette	O
BASIC	O
.	O
</s>
<s>
While	O
IBM	O
did	O
not	O
publish	O
the	O
BIOS	B-Operating_System
source	O
code	O
,	O
it	O
did	O
promise	O
to	O
publish	O
BIOS	B-Operating_System
entry	B-Language
points	I-Language
.	O
</s>
<s>
With	O
certain	O
models	O
to	O
the	O
IBM	O
PS/2	O
line	O
,	O
Micro	B-Device
Channel	I-Device
Architecture	I-Device
(	O
MCA	O
)	O
was	O
also	O
introduced	O
.	O
</s>
<s>
MCA	O
was	O
conceptually	O
similar	O
to	O
the	O
channel	O
architecture	O
of	O
the	O
IBM	B-Application
System/360	I-Application
mainframes	O
.	O
</s>
<s>
MCA	O
was	O
technically	O
superior	O
to	O
ISA	B-Architecture
and	O
allowed	O
for	O
higher	O
speed	O
communications	O
within	O
the	O
system	O
.	O
</s>
<s>
The	O
majority	O
of	O
MCA	O
's	O
features	O
would	O
be	O
seen	O
in	O
later	O
buses	O
with	O
the	O
exception	O
of	O
:	O
streaming-data	O
procedure	O
,	O
channel-check	O
reporting	O
,	O
error	O
logging	O
and	O
internal	O
bus-level	O
video	O
pass-through	O
for	O
devices	O
like	O
the	O
IBM	B-Device
8514	I-Device
.	O
</s>
<s>
Transfer	O
speeds	O
were	O
on	O
par	O
with	O
the	O
much	O
later	O
PCI	B-Protocol
standard	O
.	O
</s>
<s>
MCA	O
allowed	O
one-to-one	O
,	O
card	O
to	O
card	O
,	O
and	O
multi-card	O
to	O
processor	O
simultaneous	O
transaction	O
management	O
which	O
is	O
a	O
feature	O
of	O
the	O
PCI-X	O
bus	O
format	O
.	O
</s>
<s>
Bus	O
mastering	O
capability	O
,	O
bus	O
arbitration	O
,	O
and	O
a	O
primitive	O
form	O
of	O
plug-and-play	B-Device
management	O
of	O
hardware	O
were	O
all	O
benefits	O
of	O
MCA	O
.	O
</s>
<s>
Gilbert	O
Held	O
in	O
his	O
2000	O
book	O
Server	B-Application
Management	O
observes	O
:	O
"	O
MCA	O
used	O
an	O
early	O
(	O
and	O
user-hostile	O
)	O
version	O
of	O
what	O
we	O
know	O
now	O
as	O
'	O
Plug-N	O
′-Play	O
 '	O
,	O
requiring	O
a	O
special	O
setup	O
disk	O
for	O
each	O
machine	O
and	O
each	O
card.	O
"	O
</s>
<s>
When	O
setting	O
up	O
the	O
card	O
with	O
its	O
disk	O
,	O
all	O
choices	O
for	O
interrupts	O
and	O
other	O
changes	O
were	O
accomplished	O
automatically	O
by	O
the	O
PC	O
reading	O
the	O
old	O
configuration	O
from	O
the	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
This	O
made	O
necessary	O
changes	O
,	O
then	O
recorded	O
the	O
new	O
configuration	O
to	O
the	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
This	O
meant	O
that	O
the	O
user	O
must	O
keep	O
that	O
same	O
floppy	B-Device
disk	I-Device
matched	O
to	O
that	O
particular	O
PC	O
.	O
</s>
<s>
For	O
a	O
small	O
organization	O
with	O
a	O
few	O
PCs	B-Device
,	O
this	O
was	O
annoying	O
,	O
but	O
less	O
expensive	O
and	O
time	O
consuming	O
than	O
bringing	O
in	O
a	O
PC	O
technician	O
to	O
do	O
installation	O
.	O
</s>
<s>
But	O
for	O
large	O
organizations	O
with	O
hundreds	O
or	O
even	O
thousands	O
of	O
PCs	B-Device
,	O
permanently	O
matching	O
each	O
PC	O
with	O
its	O
own	O
floppy	B-Device
disk	I-Device
was	O
a	O
logistical	O
nightmare	O
.	O
</s>
<s>
Without	O
the	O
original	O
,	O
(	O
and	O
correctly	O
updated	O
)	O
floppy	B-Device
disk	I-Device
,	O
no	O
changes	O
could	O
be	O
made	O
to	O
the	O
PC	O
's	O
cards	O
.	O
</s>
<s>
Up	O
until	O
that	O
time	O
,	O
some	O
companies	O
had	O
failed	O
to	O
pay	O
IBM	O
for	O
the	O
use	O
of	O
its	O
patents	O
on	O
the	O
earlier	O
generation	O
of	O
Personal	B-Device
Computer	I-Device
.	O
</s>
<s>
The	O
PS/2	O
IBM	B-Device
Model	I-Device
M	I-Device
keyboard	I-Device
used	O
the	O
same	O
101-key	O
layout	O
of	O
the	O
previous	O
IBM	B-Operating_System
PC/AT	I-Operating_System
Extended	O
keyboard	B-Device
,	O
itself	O
derived	O
from	O
the	O
original	O
IBM	B-Device
PC	I-Device
keyboard	I-Device
.	O
</s>
<s>
PS/2	O
systems	O
introduced	O
a	O
new	O
specification	O
for	O
the	O
keyboard	B-Device
and	O
mouse	B-Device
interfaces	O
,	O
which	O
are	O
still	O
in	O
use	O
today	O
(	O
though	O
increasingly	O
supplanted	O
by	O
USB	B-Protocol
devices	I-Protocol
)	O
and	O
are	O
thus	O
called	O
"	O
PS/2	O
"	O
interfaces	O
.	O
</s>
<s>
The	O
PS/2	O
keyboard	B-Device
interface	O
,	O
inspired	O
by	O
Apple	O
's	O
ADB	O
interface	O
,	O
was	O
electronically	O
identical	O
to	O
the	O
long-established	O
AT	B-Device
interface	O
,	O
but	O
the	O
cable	O
connector	O
was	O
changed	O
from	O
the	O
5-pin	O
DIN	B-Architecture
connector	I-Architecture
to	O
the	O
smaller	O
6-pin	O
mini-DIN	B-Protocol
interface	O
.	O
</s>
<s>
The	O
same	O
connector	O
and	O
a	O
similar	O
synchronous	O
serial	O
interface	O
was	O
used	O
for	O
the	O
PS/2	O
mouse	B-Device
port	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
PS/2	O
introduced	O
a	O
new	O
software	O
data	O
area	O
known	O
as	O
the	O
Extended	O
BIOS	B-Operating_System
Data	O
Area	O
(	O
EBDA	O
)	O
.	O
</s>
<s>
Its	O
primary	O
use	O
was	O
to	O
add	O
a	O
new	O
buffer	O
area	O
for	O
the	O
dedicated	O
mouse	B-Device
port	O
.	O
</s>
<s>
This	O
also	O
required	O
making	O
a	O
change	O
to	O
the	O
"	O
traditional	O
"	O
BIOS	B-Operating_System
Data	O
Area	O
(	O
BDA	O
)	O
which	O
was	O
then	O
required	O
to	O
point	O
to	O
the	O
base	O
address	O
of	O
the	O
EBDA	O
.	O
</s>
<s>
Another	O
new	O
PS/2	O
innovation	O
was	O
the	O
introduction	O
of	O
bidirectional	O
parallel	B-Device
ports	I-Device
which	O
,	O
in	O
addition	O
to	O
their	O
traditional	O
use	O
for	O
connecting	O
a	O
printer	O
,	O
could	O
now	O
function	O
as	O
a	O
high-speed	O
data	O
transfer	O
interface	O
.	O
</s>
<s>
This	O
allowed	O
the	O
use	O
of	O
new	O
hardware	O
such	O
as	O
parallel	B-Device
port	I-Device
scanners	O
,	O
CD-ROM	O
drives	O
,	O
and	O
also	O
enhanced	O
the	O
capabilities	O
of	O
printers	O
by	O
allowing	O
them	O
to	O
communicate	O
with	O
the	O
host	O
PC	O
and	O
send	O
back	O
signals	O
instead	O
of	O
simply	O
being	O
a	O
passive	O
output	O
device	O
.	O
</s>
<s>
Most	O
of	O
the	O
initial	O
range	O
of	O
PS/2	O
models	O
were	O
equipped	O
with	O
a	O
new	O
frame	B-Algorithm
buffer	I-Algorithm
known	O
as	O
the	O
Video	B-Protocol
Graphics	I-Protocol
Array	I-Protocol
,	O
or	O
VGA	B-Protocol
for	O
short	O
.	O
</s>
<s>
This	O
effectively	O
replaced	O
the	O
previous	O
EGA	B-Device
standard	O
.	O
</s>
<s>
VGA	B-Protocol
increased	O
graphics	O
memory	O
to	O
256KB	O
and	O
provided	O
for	O
resolutions	O
of	O
640×480	O
with	O
16	O
colors	O
,	O
and	O
with	O
256	O
colors	O
.	O
</s>
<s>
VGA	B-Protocol
also	O
provided	O
a	O
palette	O
of	O
262,144	O
colors	O
(	O
as	O
opposed	O
to	O
the	O
EGA	B-Device
palette	O
of	O
64	O
colors	O
)	O
.	O
</s>
<s>
The	O
IBM	B-Device
8514	I-Device
and	O
later	O
XGA	B-Device
computer	O
display	O
standards	O
were	O
also	O
introduced	O
on	O
the	O
PS/2	O
line	O
.	O
</s>
<s>
In	O
truth	O
,	O
all	O
XGA	B-Device
monitors	O
are	O
multimode	O
,	O
as	O
XGA	B-Device
works	O
as	O
an	O
add-on	O
card	O
to	O
a	O
built-in	O
VGA	B-Protocol
and	O
transparently	O
passes	O
the	O
VGA	B-Protocol
signal	O
through	O
when	O
not	O
operating	O
in	O
a	O
high-resolution	O
mode	O
.	O
</s>
<s>
All	O
of	O
the	O
listed	O
85xx	O
displays	O
can	O
therefore	O
sync	O
640×480	O
at	B-Device
60Hz	O
(	O
or	O
at	B-Device
70Hz	O
)	O
in	O
addition	O
to	O
any	O
higher	O
mode	O
they	O
may	O
also	O
be	O
capable	O
of	O
.	O
</s>
<s>
This	O
however	O
is	O
not	O
true	O
of	O
the	O
95xx	O
models	O
(	O
and	O
some	O
unlisted	O
85xx	O
's	O
)	O
,	O
which	O
are	O
specialist	O
workstation	B-Device
displays	O
designed	O
for	O
use	O
with	O
the	O
XGA-2	O
or	O
Image	O
Adapter/A	O
cards	O
,	O
and	O
whose	O
fixed	O
frequencies	O
all	O
exceed	O
that	O
of	O
basic	O
VGA	B-Protocol
–	O
the	O
lowest	O
of	O
their	O
commonly	O
available	O
modes	O
instead	O
being	O
at	B-Device
75Hz	O
,	O
if	O
not	O
something	O
much	O
higher	O
still	O
.	O
</s>
<s>
It	O
is	O
also	O
worth	O
noting	O
that	O
these	O
were	O
still	O
merely	O
dual	O
-	O
or	O
"	O
multiple-frequency	O
"	O
monitors	O
,	O
not	O
variable-frequency	O
(	O
also	O
known	O
as	O
multisync	O
)	O
;	O
in	O
particular	O
,	O
despite	O
running	O
happily	O
at	B-Device
,	O
and	O
,	O
an	O
(	O
e.g.	O
)	O
</s>
<s>
8514	B-Device
cannot	O
sync	O
the	O
otherwise	O
common	O
intermediate	O
SVGA	O
resolution	O
,	O
even	O
at	B-Device
the	O
relatively	O
low	O
50	O
to	O
56Hz	O
refresh	O
rates	O
initially	O
used	O
.	O
</s>
<s>
Although	O
the	O
design	O
of	O
these	O
adapters	O
did	O
not	O
become	O
an	O
industry	O
standard	O
as	O
VGA	B-Protocol
did	O
,	O
their	O
pixel	O
resolution	O
was	O
subsequently	O
widely	O
adopted	O
as	O
a	O
standard	O
by	O
other	O
manufacturers	O
,	O
and	O
XGA	B-Device
became	O
a	O
synonym	O
for	O
this	O
screen	O
resolution	O
.	O
</s>
<s>
The	O
lone	O
exception	O
were	O
the	O
bottom-rung	O
8086-based	O
Model	B-Device
25	I-Device
and	O
30	O
,	O
which	O
had	O
a	O
cut-down	O
version	O
of	O
VGA	B-Protocol
referred	O
to	O
as	O
MCGA	B-Device
;	O
the	O
286	B-General_Concept
models	O
came	O
with	O
VGA	B-Protocol
.	O
</s>
<s>
This	O
supported	O
CGA	O
graphics	O
modes	O
,	O
VGA	B-Protocol
256	O
color	O
and	O
monochrome	O
mode	O
,	O
but	O
not	O
EGA	B-Device
or	O
color	O
.	O
</s>
<s>
All	O
of	O
the	O
new	O
PS/2	O
graphics	O
systems	O
(	O
whether	O
MCGA	B-Device
,	O
VGA	B-Protocol
,	O
8514	B-Device
,	O
or	O
later	O
XGA	B-Device
)	O
used	O
a	O
15-pin	O
D-sub	B-Protocol
connector	I-Protocol
for	O
video	O
out	O
.	O
</s>
<s>
This	O
used	O
analog	O
RGB	O
signals	O
,	O
rather	O
than	O
four	O
or	O
six	O
digital	O
color	O
signals	O
as	O
on	O
previous	O
CGA	O
and	O
EGA	B-Device
monitors	O
.	O
</s>
<s>
Unlike	O
earlier	O
systems	O
such	O
as	O
MDA	B-Device
and	O
Hercules	B-Device
,	O
this	O
was	O
transparent	O
to	O
software	O
,	O
so	O
all	O
programs	O
supporting	O
the	O
new	O
standards	O
could	O
run	O
unmodified	O
whichever	O
type	O
of	O
display	O
was	O
attached	O
.	O
</s>
<s>
The	O
VGA	B-Protocol
connector	I-Protocol
became	O
the	O
de-facto	O
standard	O
for	O
connecting	O
monitors	O
and	O
projectors	O
on	O
both	O
PC	O
and	O
non-PC	O
hardware	O
over	O
the	O
course	O
of	O
the	O
early	O
1990s	O
,	O
replacing	O
a	O
variety	O
of	O
earlier	O
connectors	O
.	O
</s>
<s>
Apple	O
had	O
first	O
popularized	O
the	O
3.5	B-Device
"	I-Device
floppy	B-Device
on	O
the	O
Macintosh	O
line	O
and	O
IBM	O
brought	O
them	O
to	O
the	O
PC	O
in	O
1986	O
with	O
the	O
PC	B-Device
Convertible	I-Device
.	O
</s>
<s>
In	O
addition	O
,	O
they	O
could	O
be	O
had	O
as	O
an	O
optional	O
feature	O
on	O
the	O
XT	B-Device
and	O
AT	B-Device
.	O
</s>
<s>
The	O
PS/2	O
line	O
used	O
entirely	O
3.5	B-Device
"	I-Device
drives	O
which	O
assisted	O
in	O
their	O
quick	O
adoption	O
by	O
the	O
industry	O
,	O
although	O
the	O
lack	O
of	O
5.25	B-Device
"	I-Device
drive	O
bays	O
in	O
the	O
computers	O
created	O
problems	O
later	O
on	O
in	O
the	O
1990s	O
as	O
they	O
could	O
not	O
accommodate	O
internal	O
CD-ROM	O
drives	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
lack	O
of	O
built-in	O
5.25	B-Device
"	I-Device
floppy	B-Device
drives	I-Device
meant	O
that	O
PS/2	O
users	O
could	O
not	O
immediately	O
run	O
the	O
large	O
body	O
of	O
existing	O
IBM-compatible	O
software	O
.	O
</s>
<s>
However	O
IBM	O
made	O
available	O
optional	O
external	O
5.25	B-Device
"	I-Device
drives	O
,	O
with	O
internal	O
adapters	O
for	O
the	O
early	O
PS/2	O
models	O
,	O
to	O
enable	O
data	O
transfer	O
.	O
</s>
<s>
In	O
the	O
initial	O
lineup	O
,	O
IBM	O
used	O
720KB	O
double	O
density	O
(	O
DD	O
)	O
capacity	O
drives	O
on	O
the	O
8086-based	O
models	O
and	O
1440KB	O
high	O
density	O
(	O
HD	O
)	O
on	O
the	O
80286-based	O
and	O
higher	O
models	O
.	O
</s>
<s>
The	O
PS/2	O
floppy	B-Device
drives	I-Device
lacked	O
a	O
capacity	O
detector	O
.	O
</s>
<s>
1440KB	O
floppies	B-Device
had	O
a	O
hole	O
so	O
that	O
drives	O
could	O
identify	O
them	O
from	O
720KB	O
floppies	B-Device
,	O
preventing	O
users	O
from	O
formatting	O
the	O
smaller	O
capacity	O
disks	O
to	O
the	O
higher	O
capacity	O
(	O
doing	O
so	O
would	O
work	O
,	O
but	O
with	O
a	O
higher	O
tendency	O
of	O
data	O
loss	O
)	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
this	O
a	O
720	O
KB	O
floppy	B-Device
could	O
be	O
formatted	O
to	O
1440KB	O
in	O
a	O
PS/2	O
,	O
but	O
the	O
resulting	O
floppy	B-Device
would	O
only	O
be	O
readable	O
by	O
a	O
PS/2	O
machine	O
.	O
</s>
<s>
PS/2s	O
primarily	O
used	O
Mitsubishi	O
floppy	B-Device
drives	I-Device
and	O
did	O
not	O
use	O
a	O
separate	O
Molex	O
power	O
connector	O
;	O
the	O
data	O
cable	O
also	O
contained	O
the	O
power	O
supply	O
lines	O
.	O
</s>
<s>
The	O
PS/2	O
used	O
several	O
different	O
types	O
of	O
internal	B-Device
hard	I-Device
drives	I-Device
.	O
</s>
<s>
Early	O
models	O
used	O
MFM	B-Protocol
or	O
ESDI	B-Architecture
drives	O
.	O
</s>
<s>
Some	O
desktop	O
models	O
used	O
combo	O
power/data	O
cables	O
similar	O
to	O
the	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
Later	O
models	O
used	O
DBA	O
ESDI	B-Architecture
or	O
Parallel	O
SCSI	B-Architecture
.	O
</s>
<s>
Typically	O
,	O
desktop	O
PS/2	O
models	O
only	O
permitted	O
use	O
of	O
one	O
hard	B-Device
drive	I-Device
inside	O
the	O
computer	B-General_Concept
case	I-General_Concept
.	O
</s>
<s>
Additional	O
storage	O
could	O
be	O
attached	O
externally	O
using	O
the	O
optional	O
SCSI	B-Architecture
interface	O
.	O
</s>
<s>
Later	O
PS/2	O
models	O
introduced	O
the	O
72-pin	O
SIMM	B-General_Concept
which	O
became	O
the	O
de	O
facto	O
standard	O
for	O
RAM	B-Architecture
modules	O
by	O
the	O
mid-1990s	O
in	O
mid-to-late	O
486	B-General_Concept
and	O
nearly	O
all	O
Pentium	B-General_Concept
desktop	O
systems	O
.	O
</s>
<s>
72-pin	O
SIMMs	B-General_Concept
were	O
32/36	O
bits	O
wide	O
and	O
replaced	O
the	O
old	O
30-pin	O
SIMM	B-General_Concept
(	O
8/9	O
-bit	O
)	O
standard	O
.	O
</s>
<s>
The	O
older	O
SIMMs	B-General_Concept
were	O
much	O
less	O
convenient	O
because	O
they	O
had	O
to	O
be	O
installed	O
in	O
sets	O
of	O
two	O
or	O
four	O
to	O
match	O
the	O
width	O
of	O
the	O
CPU	B-General_Concept
's	O
16-bit	O
(	O
Intel	B-General_Concept
80286	I-General_Concept
and	O
80386SX	O
)	O
or	O
32-bit	O
(	O
80386	B-General_Concept
and	O
80486	B-General_Concept
)	O
data	O
bus	O
,	O
and	O
would	O
have	O
been	O
extremely	O
inconvenient	O
to	O
use	O
in	O
Pentium	B-General_Concept
systems	O
(	O
which	O
featured	O
a	O
64-bit	O
memory	O
bus	O
)	O
.	O
</s>
<s>
72-pin	O
SIMMs	B-General_Concept
were	O
also	O
made	O
with	O
greater	O
capacities	O
(	O
starting	O
at	B-Device
1mb	O
and	O
ultimately	O
reaching	O
128	O
MB	O
,	O
vs	O
256	O
KB	O
to	O
16	O
MB	O
and	O
more	O
commonly	O
no	O
more	O
than	O
4	O
MB	O
for	O
30-pin	O
)	O
and	O
in	O
a	O
more	O
finely	O
graduated	O
range	O
(	O
powers	O
of	O
2	O
,	O
instead	O
of	O
powers	O
of	O
4	O
)	O
.	O
</s>
<s>
Many	O
PS/2	O
models	O
also	O
used	O
proprietary	O
IBM	O
SIMMs	B-General_Concept
and	O
could	O
not	O
be	O
fitted	O
with	O
commonly	O
available	O
types	O
.	O
</s>
<s>
However	O
industry	O
standard	O
SIMMs	B-General_Concept
could	O
be	O
modified	O
to	O
work	O
in	O
PS/2	O
machines	O
if	O
the	O
SIMM-presence	O
and	O
SIMM-type	O
detection	O
bridges	O
,	O
or	O
associated	O
contacts	O
,	O
were	O
correctly	O
rewired	O
.	O
</s>
<s>
At	B-Device
launch	O
,	O
the	O
PS/2	O
family	O
comprised	O
the	O
Model	B-Device
30	I-Device
,	O
50	O
,	O
60	O
and	O
80	O
;	O
the	O
Model	B-Device
25	I-Device
was	O
launched	O
a	O
few	O
months	O
later	O
.	O
</s>
<s>
The	O
PS/2	O
Models	O
25	O
and	O
30	O
(	O
IBM	O
8525	O
and	O
8530	O
,	O
respectively	O
)	O
were	O
the	O
lowest-end	O
models	O
in	O
the	O
lineup	O
and	O
meant	O
to	O
replace	O
the	O
IBM	B-Device
PC	I-Device
and	O
XT	B-Device
.	O
</s>
<s>
Model	O
25s	O
came	O
with	O
either	O
an	O
8086	O
CPU	B-General_Concept
running	O
at	B-Device
8MHz	O
,	O
512KB	O
of	O
RAM	B-Architecture
,	O
and	O
720KB	O
floppy	B-Device
disks	I-Device
,	O
or	O
80286	B-General_Concept
CPU	B-General_Concept
.	O
</s>
<s>
The	O
8086s	O
had	O
ISA	B-Architecture
expansion	O
slots	O
and	O
a	O
built-in	O
MCGA	B-Device
monitor	O
,	O
which	O
could	O
be	O
either	O
color	O
or	O
monochrome	O
,	O
while	O
the	O
80286	B-General_Concept
models	O
came	O
with	O
VGA	B-Protocol
monitor	I-Protocol
and	O
ISA	B-Architecture
expansion	O
slots	O
.	O
</s>
<s>
A	O
cut-down	O
Model	B-Device
M	I-Device
with	O
no	O
numeric	O
keypad	O
was	O
standard	O
,	O
with	O
the	O
normal	O
keyboard	B-Device
being	O
an	O
extra-cost	O
option	O
.	O
</s>
<s>
There	O
was	O
a	O
very	O
rare	O
later	O
model	O
called	O
the	O
PS/2	O
Model	O
25-SX	O
which	O
sported	O
either	O
a	O
16MHz	O
or	O
20MHz	O
386	B-General_Concept
CPU	B-General_Concept
,	O
up	O
to	O
12MB	O
of	O
memory	O
,	O
IDE	B-Protocol
hard	I-Protocol
drive	I-Protocol
,	O
VGA	B-Protocol
Monitor	I-Protocol
and	O
16bit	O
ISA	B-Architecture
slots	I-Architecture
making	O
it	O
the	O
highest	O
available	O
model	B-Device
25	I-Device
available	O
denoted	O
by	O
model	O
number	O
8525-L41	O
.	O
</s>
<s>
The	O
Model	B-Device
30	I-Device
had	O
either	O
an	O
8086	O
or	O
286	B-General_Concept
CPU	B-General_Concept
and	O
sported	O
the	O
full	O
101-key	O
keyboard	B-Device
and	O
standalone	O
monitor	O
along	O
with	O
three	O
8-bit	O
ISA	B-Architecture
expansion	O
slots	O
.	O
</s>
<s>
8086	O
models	O
had	O
720KB	O
floppies	B-Device
while	O
286	B-General_Concept
models	O
had	O
1440KB	O
ones	O
.	O
</s>
<s>
Both	O
the	O
Model	B-Device
25	I-Device
and	O
30	O
could	O
have	O
an	O
optional	O
20MB	O
ST-506	B-Device
hard	B-Device
disk	I-Device
(	O
which	O
in	O
the	O
Model	B-Device
25	I-Device
took	O
the	O
place	O
of	O
the	O
second	O
floppy	B-Device
drive	I-Device
if	O
so	O
equipped	O
and	O
used	O
a	O
proprietary	O
3.5	B-Device
"	I-Device
form	O
factor	O
)	O
.	O
</s>
<s>
286-based	O
Model	O
30s	O
are	O
otherwise	O
a	O
full	O
AT-class	O
machine	O
and	O
support	O
up	O
to	O
4MB	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
Later	O
ISA	B-Architecture
PS/2	O
models	O
comprised	O
the	O
Model	B-Device
30	I-Device
286	I-Device
(	O
a	O
Model	B-Device
30	I-Device
with	O
an	O
Intel	B-General_Concept
286	I-General_Concept
CPU	B-General_Concept
)	O
,	O
Model	O
35	O
(	O
IBM	O
8535	O
)	O
and	O
Model	O
40	O
(	O
IBM	O
8540	O
)	O
with	O
Intel	B-General_Concept
386SX	I-General_Concept
or	O
IBM	B-Device
386SLC	I-Device
processors	O
.	O
</s>
<s>
The	O
higher-numbered	O
models	O
(	O
above	O
50	O
)	O
were	O
equipped	O
with	O
the	O
Micro	B-Device
Channel	I-Device
bus	O
and	O
mostly	O
ESDI	B-Architecture
or	O
SCSI	B-Architecture
hard	B-Device
drives	I-Device
(	O
models	O
60-041	O
and	O
80-041	O
had	O
MFM	B-Protocol
hard	B-Device
drives	I-Device
)	O
.	O
</s>
<s>
PS/2	O
Models	O
50	O
(	O
IBM	O
8550	O
)	O
and	O
60	O
(	O
IBM	O
8560	O
)	O
used	O
the	O
Intel	B-General_Concept
286	I-General_Concept
processor	O
,	O
the	O
PS/2	O
Models	O
70	O
(	O
IBM	O
8570	O
)	O
and	O
80	O
used	O
the	O
386DX	B-General_Concept
,	O
while	O
the	O
mid-range	O
PS/2	O
Model	O
55SX	O
(	O
IBM	O
8555-081	O
)	O
and	O
used	O
the	O
16/32	O
-bit	O
386SX	O
processor	O
.	O
</s>
<s>
The	O
Model	O
50	O
was	O
revised	O
to	O
the	O
Model	O
50Z	O
still	O
with	O
10MHz	O
80286	B-General_Concept
processor	O
,	O
but	O
with	O
memory	O
run	O
at	B-Device
zero	O
wait	O
state	O
,	O
and	O
a	O
switch	O
to	O
ESDI	B-Architecture
hard	B-Device
drives	I-Device
.	O
</s>
<s>
Later	O
Model	O
70	O
and	O
80	O
variants	O
(	O
B-xx	O
)	O
also	O
used	O
25MHz	O
Intel	B-General_Concept
486	I-General_Concept
processors	O
,	O
in	O
a	O
complex	O
called	O
the	O
Power	O
Platform	O
.	O
</s>
<s>
The	O
PS/2	O
Models	O
90	O
(	O
IBM	O
8590/9590	O
)	O
and	O
95	O
(	O
IBM	O
8595/9595/9595A	O
)	O
used	O
Processor	O
Complex	O
daughterboards	O
holding	O
the	O
CPU	B-General_Concept
,	O
memory	O
controller	O
,	O
MCA	O
interface	O
,	O
and	O
other	O
system	O
components	O
.	O
</s>
<s>
The	O
available	O
Processor	O
Complex	O
options	O
ranged	O
from	O
the	O
20MHz	O
Intel	B-General_Concept
486	I-General_Concept
to	O
the	O
90MHz	O
Pentium	B-General_Concept
and	O
were	O
fully	O
interchangeable	O
.	O
</s>
<s>
The	O
IBM	B-Device
PC	I-Device
Server	B-Application
500	O
,	O
which	O
has	O
a	O
motherboard	O
identical	O
to	O
the	O
9595A	O
,	O
also	O
uses	O
Processor	O
Complexes	O
.	O
</s>
<s>
Other	O
later	O
Micro	B-Device
Channel	I-Device
PS/2	O
models	O
included	O
the	O
Model	O
65SX	O
with	O
a	O
16MHz	O
386SX	O
;	O
various	O
Model	O
53	O
(	O
IBM	O
9553	O
)	O
,	O
56	O
(	O
IBM	O
8556	O
)	O
and	O
57	O
(	O
IBM	O
8557	O
)	O
variants	O
with	O
386SX	O
,	O
386SLC	B-Device
or	O
486SLC2	O
processors	O
;	O
the	O
Models	O
76	O
and	O
77	O
(	O
IBM	O
9576/9577	O
)	O
with	O
486SX	O
or	O
486DX2	O
processors	O
respectively	O
;	O
and	O
the	O
486-based	O
Model	O
85	O
(	O
IBM	O
9585	O
)	O
.	O
</s>
<s>
The	O
IBM	O
PS/2E	B-Device
(	O
IBM	O
9533	O
)	O
was	O
the	O
first	O
Energy	O
Star	O
compliant	O
personal	B-Device
computer	I-Device
.	O
</s>
<s>
It	O
had	O
a	O
50MHz	O
IBM	B-Device
486SLC	I-Device
processor	O
,	O
an	O
ISA	B-Architecture
bus	I-Architecture
,	O
four	O
PC	B-Architecture
card	I-Architecture
slots	O
,	O
and	O
an	O
IDE	B-Protocol
hard	I-Protocol
drive	I-Protocol
interface	O
.	O
</s>
<s>
The	O
environmentally	O
friendly	O
PC	O
borrowed	O
many	O
components	O
from	O
the	O
ThinkPad	B-Operating_System
line	O
and	O
was	O
composed	O
of	O
recycled	O
plastics	O
,	O
designed	O
to	O
be	O
easily	O
recycled	O
at	B-Device
the	O
end	O
of	O
its	O
life	O
,	O
and	O
used	O
very	O
little	O
power	O
.	O
</s>
<s>
The	O
IBM	O
PS/2	O
Server	B-Application
195	O
and	O
295	O
(	O
IBM	O
8600	O
)	O
were	O
486-based	O
dual-bus	O
MCA	O
network	B-Application
servers	I-Application
supporting	O
asymmetric	B-Operating_System
multiprocessing	I-Operating_System
,	O
designed	O
by	O
Parallan	O
Computer	O
Inc	O
.	O
</s>
<s>
The	O
IBM	B-Device
PC	I-Device
Server	B-Application
720	O
(	O
IBM	O
8642	O
)	O
was	O
the	O
largest	O
MCA-based	O
server	B-Application
made	O
by	O
IBM	O
,	O
although	O
it	O
was	O
not	O
,	O
strictly	O
speaking	O
,	O
a	O
PS/2	O
model	O
.	O
</s>
<s>
It	O
could	O
be	O
fitted	O
with	O
up	O
to	O
six	O
Intel	B-General_Concept
Pentium	I-General_Concept
processors	O
interconnected	O
by	O
the	O
Corollary	O
C-bus	O
and	O
up	O
to	O
eighteen	O
SCSI	B-Architecture
hard	B-Device
disks	I-Device
.	O
</s>
<s>
IBM	O
also	O
produced	O
several	O
portable	O
and	O
laptop	B-Device
PS/2s	O
,	O
including	O
the	O
Model	B-Device
L40	I-Device
(	O
ISA-bus	O
386SX	O
)	O
,	O
N33	O
(	O
IBM	O
's	O
first	O
notebook-format	O
computer	O
from	O
year	O
1991	O
,	O
Model	O
8533	O
,	O
386SX	O
)	O
,	O
N51	O
(	O
386SX/SLC	O
)	O
,	O
P70	O
(	O
386DX	B-General_Concept
)	O
and	O
P75	O
(	O
486DX2	O
)	O
.	O
</s>
<s>
The	O
IBM	B-Operating_System
ThinkPad	I-Operating_System
700C	O
,	O
aside	O
from	O
being	O
labeled	O
"	O
700C	O
PS/2	O
"	O
on	O
the	O
case	O
,	O
featured	O
MCA	O
and	O
a	O
486SLC	O
CPU	B-General_Concept
.	O
</s>
<s>
The	O
6152	O
Academic	O
System	O
was	O
a	O
workstation	B-Device
computer	I-Device
developed	O
by	O
IBM	O
's	O
Academic	O
Information	O
Systems	O
(	O
ACIS	O
)	O
division	O
for	O
the	O
university	O
market	O
introduced	O
in	O
February	O
1988	O
.	O
</s>
<s>
The	O
6152	O
was	O
based	O
on	O
the	O
PS/2	O
Model	O
60	O
,	O
adding	O
a	O
RISC	O
Adapter	O
Card	O
on	O
the	O
Micro	B-Device
Channel	I-Device
bus	O
.	O
</s>
<s>
This	O
card	O
was	O
a	O
co-processor	B-General_Concept
that	O
enabled	O
the	O
6152	O
to	O
run	O
ROMP	B-Device
software	O
compiled	O
for	O
IBM	O
's	O
Academic	O
Operating	O
System	O
(	O
AOS	O
)	O
,	O
a	O
version	O
of	O
BSD	B-Operating_System
UNIX	I-Operating_System
for	O
the	O
ROMP	B-Device
that	O
was	O
only	O
available	O
to	O
select	O
colleges	O
and	O
universities	O
.	O
</s>
<s>
The	O
RISC	O
Adapter	O
Card	O
contained	O
the	O
ROMP-C	O
microprocessor	O
(	O
an	O
enhanced	O
version	O
of	O
the	O
ROMP	B-Device
that	O
first	O
appeared	O
in	O
the	O
IBM	B-Device
RT	I-Device
PC	I-Device
workstations	B-Device
)	O
,	O
a	O
memory	B-General_Concept
management	I-General_Concept
unit	I-General_Concept
(	O
the	O
ROMP	B-Device
had	O
virtual	B-Architecture
memory	I-Architecture
)	O
,	O
a	O
floating-point	B-General_Concept
coprocessor	B-General_Concept
,	O
and	O
up	O
to	O
8MB	O
of	O
memory	O
for	O
use	O
by	O
the	O
ROMP	B-Device
.	O
</s>
<s>
The	O
6152	O
was	O
the	O
first	O
computer	O
to	O
use	O
the	O
ROMP-C	O
,	O
which	O
would	O
later	O
be	O
introduced	O
in	O
new	O
RT	B-Device
PC	I-Device
models	O
.	O
</s>
<s>
During	O
the	O
1980s	O
,	O
IBM	O
's	O
advertising	O
of	O
the	O
original	B-Device
PC	I-Device
and	O
its	O
other	O
product	O
lines	O
had	O
frequently	O
used	O
the	O
likeness	O
of	O
Charlie	O
Chaplin	O
.	O
</s>
<s>
With	O
what	O
was	O
widely	O
seen	O
as	O
a	O
technically	O
competent	O
but	O
cynical	O
attempt	O
to	O
gain	O
undisputed	O
control	O
of	O
the	O
market	O
,	O
IBM	O
unleashed	O
an	O
industry	O
backlash	O
,	O
which	O
went	O
on	O
to	O
standardize	O
VESA	O
,	O
EISA	O
and	O
PCI	B-Protocol
.	O
</s>
<s>
In	O
large	O
part	O
,	O
IBM	O
failed	O
to	O
establish	O
a	O
link	O
in	O
the	O
consumer	O
's	O
mind	O
between	O
the	O
PS/2	O
MicroChannel	B-Device
architecture	I-Device
and	O
the	O
immature	O
OS/2	B-Application
1.x	O
operating	O
system	O
;	O
the	O
more	O
capable	O
OS/2	B-Application
version	O
2.0	O
did	O
not	O
release	O
until	O
1992	O
.	O
</s>
<s>
The	O
firm	O
suffered	O
massive	O
financial	O
losses	O
for	O
the	O
remainder	O
of	O
the	O
1980s	O
,	O
forfeiting	O
its	O
previously	O
unquestioned	O
position	O
as	O
the	O
industry	O
leader	O
,	O
and	O
eventually	O
lost	O
its	O
status	O
as	O
the	O
largest	O
manufacturer	O
of	O
personal	B-Device
computers	I-Device
,	O
first	O
to	O
Compaq	O
and	O
then	O
to	O
Dell	O
.	O
</s>
<s>
After	O
the	O
failure	O
of	O
the	O
PS/2	O
line	O
to	O
establish	O
a	O
new	O
standard	O
,	O
IBM	O
was	O
forced	O
to	O
revert	O
to	O
building	O
ISA	B-Architecture
PCsfollowing	O
the	O
industry	O
it	O
had	O
once	O
ledwith	O
the	O
low-end	O
PS/1	B-Device
line	O
and	O
later	O
with	O
the	O
more	O
compatible	O
Aptiva	O
and	O
PS/ValuePoint	B-Device
lines	O
.	O
</s>
