<s>
The	O
IBM	B-Device
PS/1	I-Device
is	O
a	O
brand	O
for	O
a	O
line	O
of	O
personal	B-Device
computers	I-Device
that	O
marked	O
IBM	O
's	O
return	O
to	O
the	O
home	O
market	O
in	O
1990	O
,	O
five	O
years	O
after	O
the	O
IBM	B-Device
PCjr	I-Device
.	O
</s>
<s>
Like	O
the	O
PCjr	B-Device
,	O
the	O
PS/1	O
'	O
s	O
name	O
suggested	O
a	O
more	O
limited	O
machine	O
than	O
IBM	O
's	O
business	O
line	O
,	O
the	O
PS/2	B-Device
.	O
</s>
<s>
However	O
,	O
unlike	O
the	O
PS/2	B-Device
,	O
the	O
PS/1	O
was	O
based	O
upon	O
architecture	O
closer	O
to	O
the	O
AT	O
and	O
compatibles	O
,	O
for	O
example	O
using	O
ISA	B-Architecture
,	O
plain	O
VGA	O
,	O
and	O
IDE	O
.	O
</s>
<s>
Although	O
the	O
first	O
models	O
used	O
custom-designed	O
components	O
and	O
design	O
,	O
later	O
desktop	O
and	O
tower	B-General_Concept
models	O
used	O
mostly	O
standard	O
components	O
.	O
</s>
<s>
The	O
earlier	O
models	O
included	O
a	O
ROM	O
with	O
IBM	O
's	O
PC	B-Operating_System
DOS	I-Operating_System
and	O
a	O
graphical	O
shell	O
,	O
however	O
the	O
system	O
was	O
compatible	O
with	O
other	O
DOS	O
implementations	O
and	O
the	O
shell	O
could	O
be	O
installed	O
on	O
the	O
hard	O
drive	O
.	O
</s>
<s>
There	O
were	O
several	O
form	O
factors	O
used	O
during	O
the	O
PS/1	O
'	O
s	O
production	O
,	O
with	O
the	O
2133	O
and	O
2155	O
cases	O
used	O
for	O
several	O
model	O
years	O
while	O
the	O
2168	O
tower	B-General_Concept
case	I-General_Concept
was	O
offered	O
later	O
in	O
later	O
models	O
of	O
the	O
PS/1	O
lineup	O
:	O
</s>
<s>
2168	O
Tower	B-General_Concept
unit	O
.	O
</s>
<s>
The	O
original	O
PS/1	O
(	O
Model	O
2011	O
)	O
,	O
based	O
on	O
a	O
10MHz	O
Intel	B-General_Concept
80286	I-General_Concept
CPU	O
,	O
was	O
designed	O
to	O
be	O
easy	O
to	O
set	O
up	O
and	O
use	O
.	O
</s>
<s>
IBM	O
also	O
released	O
a	O
5.25	O
"	O
disk	O
drive	O
unit	O
,	O
a	O
$169	O
ISA	B-Architecture
Adapter	O
Card	O
Unit	O
(	O
ACU	O
)	O
to	O
install	O
third-party	O
expansion	O
cards	O
,	O
and	O
a	O
$995	O
CD-ROM	O
drive	O
,	O
based	O
on	O
a	O
Western	O
Digital	O
SCSI	O
chip	O
,	O
that	O
fit	O
underneath	O
the	O
case	O
.	O
</s>
<s>
Some	O
of	O
the	O
lower-end	O
PS/1	O
models	O
suffered	O
from	O
very	O
limited	O
expansion	O
capabilities	O
,	O
since	O
they	O
lacked	O
standard	O
ISA	B-Architecture
expansion	O
slots	O
.	O
</s>
<s>
The	O
2121	O
series	O
computers	O
used	O
the	O
same	O
form	O
factor	O
as	O
the	O
2011	O
series	O
,	O
but	O
included	O
up	O
to	O
two	O
ISA	B-Architecture
slots	I-Architecture
inside	O
the	O
case	O
.	O
</s>
<s>
Model	O
US	O
List	O
MB	O
FRU	O
CPU	O
ISA	B-Architecture
Slots	I-Architecture
RAM	O
VRAM	O
Hard-Drive	O
Serial	O
/	O
Modem	O
2121-C42	O
$	O
1,699	O
92F9690	O
Intel	O
80386SX	O
@	O
16	O
MHz	O
0	O
2	O
MB	O
256KB	O
95F4720	O
(	O
40	O
MB	O
IDE	O
)	O
2400	O
baud	O
modem	O
2121-B82	O
$	O
2,199	O
92F9690	O
Intel	O
80386SX	O
@	O
16	O
MHz	O
2	O
2	O
MB	O
256KB	O
92F9943	O
(	O
80	O
MB	O
IDE	O
)	O
2400	O
baud	O
modem	O
2121-C92	O
?	O
</s>
<s>
IBM	O
made	O
the	O
decision	O
to	O
put	O
the	O
DC	O
power	O
supply	O
in	O
the	O
monitor	O
,	O
making	O
use	O
of	O
third-party	O
monitors	O
difficult	O
and	O
essentially	O
impractical	O
and	O
limiting	O
the	O
usefulness	O
of	O
the	O
computer	O
if	O
the	O
monitor	O
needed	O
service	O
(	O
similar	O
to	O
the	O
problems	O
of	O
the	O
Coleco	B-Device
Adam	I-Device
and	O
Amstrad	O
1512	O
years	O
earlier	O
)	O
.	O
</s>
<s>
Similar	O
to	O
a	O
few	O
Tandy	O
1000	O
models	O
,	O
the	O
early	O
2011	O
and	O
2121	O
had	O
an	O
operating	O
system	O
(	O
PC	B-Operating_System
DOS	I-Operating_System
4.01	O
)	O
built	O
into	O
ROM	O
,	O
rather	O
than	O
loading	O
it	O
from	O
a	O
hard	O
drive	O
.	O
</s>
<s>
Later	O
PS/1s	O
featured	O
standard	O
LPX-architecture	O
motherboard	O
.	O
</s>
<s>
Many	O
of	O
these	O
later	O
PS/1s	O
shipped	O
from	O
the	O
factory	O
with	O
MS-DOS	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
,	O
rather	O
than	O
IBM	O
's	O
PC	B-Operating_System
DOS	I-Operating_System
or	O
OS/2	B-Application
.	O
</s>
<s>
An	O
early	O
2133	O
model	O
did	O
come	O
preloaded	O
with	O
OS/2	B-Application
2.1	O
.	O
</s>
<s>
This	O
was	O
because	O
IBM	O
targeted	O
OS/2	B-Application
for	O
high-end	O
computing	O
machines	O
with	O
more	O
power	O
.	O
</s>
