<s>
The	O
3B	B-Device
series	I-Device
computers	I-Device
are	O
a	O
line	O
of	O
minicomputers	O
produced	O
from	O
the	O
late	O
1970s	O
by	O
AT&T	O
Computer	O
Systems	O
 '	O
Western	O
Electric	O
subsidiary	O
for	O
use	O
with	O
the	O
company	O
's	O
UNIX	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
The	O
line	O
primarily	O
consists	O
of	O
the	O
models	O
3B20	O
,	O
3B5	O
,	O
3B15	O
,	O
3B2	B-Device
,	O
and	O
3B4000	O
.	O
</s>
<s>
The	O
series	O
is	O
notable	O
for	O
controlling	O
a	O
series	O
of	O
electronic	B-Device
switching	I-Device
systems	I-Device
for	O
telecommunication	O
,	O
for	O
general	O
computing	O
purposes	O
,	O
and	O
for	O
serving	O
as	O
the	O
historical	O
software	O
porting	O
base	O
for	O
commercial	O
UNIX	B-Application
.	O
</s>
<s>
The	O
general	O
purpose	O
family	O
of	O
3B	B-Device
computer	O
systems	O
includes	O
the	O
3B2	B-Device
,	O
3B5	O
,	O
3B15	O
,	O
3B20S	O
,	O
and	O
3B4000	O
.	O
</s>
<s>
They	O
run	O
the	O
AT&T	O
UNIX	B-Application
operating	I-Application
system	I-Application
and	O
were	O
named	O
after	O
the	O
successful	O
3B20D	O
High	O
Availability	O
processor	O
.	O
</s>
<s>
In	O
1984	O
,	O
after	O
regulatory	O
constraints	O
were	O
lifted	O
,	O
AT&T	O
introduced	O
the	O
3B20D	O
,	O
3B20S	O
,	O
3B5	O
,	O
and	O
3B2	B-Device
to	O
the	O
general	O
computer	O
market	O
,	O
a	O
move	O
which	O
some	O
commentators	O
saw	O
as	O
an	O
attempt	O
to	O
compete	O
with	O
IBM	O
.	O
</s>
<s>
In	O
Europe	O
,	O
the	O
3B	B-Device
computers	I-Device
were	O
distributed	O
by	O
Italian	O
firm	O
Olivetti	B-Operating_System
,	O
in	O
which	O
AT&T	O
had	O
a	O
minority	O
shareholding	O
.	O
</s>
<s>
Having	O
produced	O
70,000	O
units	O
,	O
the	O
AT&T	O
Oklahoma	O
City	O
plant	O
stopped	O
manufacturing	O
3B	B-Device
machines	O
at	O
the	O
end	O
of	O
1993	O
,	O
with	O
the	O
3B20D	O
to	O
be	O
the	O
last	O
units	O
manufactured	O
.	O
</s>
<s>
The	O
original	O
series	O
of	O
3B	B-Device
computers	I-Device
includes	O
the	O
models	O
3B20C	B-Device
,	O
3B20D	O
,	O
3B21D	B-Device
,	O
and	O
3B21E	O
.	O
</s>
<s>
These	O
systems	O
are	O
32-bit	O
microprogrammed	B-Device
duplex	O
(	O
redundant	O
)	O
high	O
availability	O
processor	O
units	O
running	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
They	O
were	O
first	O
produced	O
in	O
the	O
late	O
1970s	O
at	O
the	O
WECo	O
factory	O
in	O
Lisle	O
,	O
Illinois	O
,	O
for	O
telecommunications	O
applications	O
including	O
the	O
4ESS	B-Device
and	O
5ESS	B-Device
systems	O
.	O
</s>
<s>
They	O
use	O
the	O
Duplex	O
Multi	O
Environment	O
Real	O
Time	O
(	O
DMERT	B-Operating_System
)	O
operating	O
system	O
which	O
was	O
renamed	O
UNIX-RTR	B-Operating_System
(	O
Real	O
Time	O
Reliable	O
)	O
in	O
1982	O
.	O
</s>
<s>
The	O
Data	O
Manipulation	O
Unit	O
(	O
DMU	O
)	O
provides	O
arithmetic	O
and	O
logic	O
operations	O
on	O
32-bit	O
words	O
using	O
AMD	B-General_Concept
2901	I-General_Concept
bipolar	O
4-bit	O
processor	O
elements	O
.	O
</s>
<s>
The	O
3B20C	B-Device
was	O
briefly	O
available	O
as	O
a	O
high-availability	O
fault	O
tolerant	O
multiprocessing	B-Operating_System
general	O
purpose	O
computer	O
in	O
the	O
commercial	O
market	O
in	O
1984	O
.	O
</s>
<s>
It	O
consists	O
of	O
a	O
virtual	O
"	O
emulated	O
"	O
3B20D	O
environment	O
running	O
on	O
a	O
stand-alone	O
general	O
purpose	O
computer	O
;	O
the	O
system	O
was	O
ported	O
to	O
many	O
computers	O
,	O
but	O
primarily	O
runs	O
on	O
the	O
Sun	O
Microsystems	O
Solaris	B-Application
environment	O
.	O
</s>
<s>
There	O
were	O
improvements	O
to	O
the	O
3B20D	O
UNIX-RTR	B-Operating_System
system	O
in	O
both	O
software	O
and	O
hardware	O
in	O
the	O
1980s	O
,	O
1990s	O
,	O
2000s	O
,	O
and	O
2010s	O
.	O
</s>
<s>
Innovations	O
included	O
disk	O
independent	O
operation	O
(	O
DIOP	O
:	O
the	O
ability	O
to	O
continue	O
essential	O
software	O
processing	O
such	O
as	O
telecommunications	O
after	O
duplex	O
failure	O
of	O
redundant	O
essential	O
disks	O
)	O
;	O
off-line	O
boot	O
(	O
the	O
ability	O
to	O
split	O
in	O
half	O
and	O
boot	O
the	O
out-of-service	O
half	O
,	O
typically	O
on	O
a	O
new	O
software	O
release	O
)	O
and	O
switch	O
forward	O
(	O
switch	O
processing	O
to	O
the	O
previously	O
out-of-service	O
half	O
)	O
;	O
upgrading	O
the	O
disks	O
to	O
solid-state	B-Device
drive	I-Device
(	O
SSD	B-Device
)	O
;	O
and	O
upgrading	O
the	O
tape	O
unit	O
to	O
CompactFlash	B-Device
.	O
</s>
<s>
The	O
processor	O
was	O
re-engineered	O
and	O
renamed	O
in	O
1992	O
as	O
the	O
3B21D	B-Device
.	O
</s>
<s>
It	O
is	O
still	O
in	O
use	O
as	O
a	O
component	O
of	O
Nokia	O
products	O
such	O
as	O
the	O
2STP	O
signal	O
transfer	O
point	O
and	O
the	O
4ESS	B-Device
and	O
5ESS	B-Device
switches	I-Device
,	O
which	O
Nokia	O
inherited	O
from	O
AT&T	O
spin-off	O
Lucent	O
Technologies	O
.	O
</s>
<s>
The	O
3B20A	O
is	O
an	O
enhanced	O
version	O
of	O
the	O
3B20S	O
,	O
adding	O
in	O
a	O
second	O
processing	O
unit	O
working	O
in	O
parallel	O
as	O
a	O
multiprocessor	B-Operating_System
unit	O
.	O
</s>
<s>
The	O
3B5	O
is	O
built	O
with	O
the	O
older	O
Western	O
Electric	O
WE	B-General_Concept
32000	I-General_Concept
32-bit	O
microprocessor	O
.	O
</s>
<s>
The	O
machine	O
is	O
approximately	O
the	O
size	O
of	O
a	O
dishwasher	B-Application
,	O
though	O
adding	O
the	O
reel-to-reel	O
tape	O
drive	O
increases	O
its	O
size	O
.	O
</s>
<s>
These	O
computers	O
use	O
SMD	B-Architecture
hard	O
drives	O
.	O
</s>
<s>
The	O
3B15	O
,	O
introduced	O
in	O
1985	O
,	O
uses	O
the	O
WE	B-General_Concept
32100	I-General_Concept
and	O
is	O
the	O
faster	O
follow-on	O
to	O
the	O
3B5	O
with	O
similar	O
large	O
form	O
factor	O
.	O
</s>
<s>
These	O
adjunct	O
processors	O
run	O
a	O
customized	O
UNIX	B-Application
kernel	O
with	O
drivers	O
for	O
SCSI	B-Architecture
(	O
APEs	O
)	O
and	O
serial	O
boards	O
(	O
ACEs	O
)	O
.	O
</s>
<s>
The	O
UNIX	B-Application
kernels	O
running	O
on	O
the	O
adjunct	O
processors	O
are	O
modified	O
to	O
allow	O
the	O
fork/exec	O
of	O
processes	O
across	O
processing	O
units	O
.	O
</s>
<s>
Generally	O
,	O
the	O
performance	O
of	O
the	O
system	O
increases	O
linearly	O
with	O
additional	O
processing	O
elements	O
,	O
however	O
the	O
lack	O
of	O
a	O
true	O
shared	B-Operating_System
memory	I-Operating_System
capability	O
requires	O
rewriting	O
applications	O
that	O
rely	O
heavily	O
on	O
this	O
feature	O
to	O
avoid	O
a	O
severe	O
performance	O
penalty	O
.	O
</s>
<s>
The	O
3B2	B-Device
was	O
introduced	O
in	O
1984	O
using	O
the	O
WE	B-General_Concept
32000	I-General_Concept
32-bit	O
microprocessor	O
at	O
8MHz	O
with	O
memory	O
management	O
chips	O
that	O
supports	O
demand	B-General_Concept
paging	I-General_Concept
.	O
</s>
<s>
The	O
3B2	B-Device
Model	O
300	O
,	O
which	O
can	O
support	O
up	O
to	O
18	O
users	O
,	O
is	O
approximately	O
high	O
and	O
the	O
3B2	B-Device
Model	O
400	O
is	O
approximately	O
high	O
.	O
</s>
<s>
The	O
300	O
was	O
soon	O
supplanted	O
by	O
the	O
3B2/310	O
running	O
at	O
10MHz	O
,	O
which	O
features	O
the	O
WE	B-General_Concept
32100	I-General_Concept
CPU	O
as	O
do	O
later	O
models	O
.	O
</s>
<s>
The	O
Model	O
400	O
,	O
introduced	O
in	O
1985	O
,	O
allows	O
more	O
peripheral	O
slots	O
and	O
more	O
memory	O
,	O
and	O
has	O
a	O
built-in	O
23	O
MB	O
QIC	B-Device
tape	O
drive	O
managed	O
by	O
a	O
floppy	B-Device
disk	I-Device
controller	I-Device
(	O
nicknamed	O
the	O
"	O
floppy	O
tape	O
"	O
)	O
.	O
</s>
<s>
These	O
three	O
models	O
use	O
standard	O
MFM	B-Protocol
"	O
hard	O
disk	O
drives	O
.	O
</s>
<s>
There	O
are	O
also	O
Model	O
100	O
and	O
Model	O
200	O
3B2	B-Device
systems	O
.	O
</s>
<s>
The	O
3B2/600	O
,	O
running	O
at	O
18MHz	O
,	O
offers	O
an	O
improvement	O
in	O
performance	O
and	O
capacity	O
:	O
it	O
features	O
a	O
SCSI	B-Architecture
controller	O
for	O
the	O
60	O
MB	O
QIC	B-Device
tape	O
and	O
two	O
internal	O
full-height	O
disk	O
drives	O
.	O
</s>
<s>
Early	O
models	O
use	O
an	O
internal	O
Emulex	O
card	O
to	O
interface	O
the	O
SCSI	B-Architecture
controller	O
with	O
ESDI	O
disks	O
,	O
with	O
later	O
models	O
using	O
SCSI	B-Architecture
drives	O
directly	O
.	O
</s>
<s>
The	O
3B2/500	O
was	O
the	O
next	O
model	O
to	O
appear	O
,	O
essentially	O
a	O
3B2/600	O
with	O
enough	O
components	O
removed	O
to	O
fit	O
into	O
a	O
400	O
case	O
;	O
one	O
internal	O
disk	O
drive	O
and	O
several	O
backplane	O
slots	O
are	O
sacrificed	O
in	O
this	O
conversion	O
.	O
</s>
<s>
The	O
3B2/700	O
is	O
an	O
uprated	O
version	O
of	O
the	O
600	O
featuring	O
a	O
slightly	O
faster	O
processor	O
(	O
WE	O
32200	O
at	O
22MHz	O
)	O
,	O
and	O
the	O
3B2/1000	O
is	O
an	O
additional	O
step	O
in	O
this	O
direction	O
(	O
WE	O
32200	O
at	O
24MHz	O
)	O
.	O
</s>
<s>
Officially	O
named	O
the	O
AT&T	B-Device
UNIX	I-Device
PC	I-Device
,	O
AT&T	O
introduced	O
a	O
desktop	B-Device
computer	I-Device
in	O
1985	O
that	O
is	O
often	O
dubbed	O
the	O
3B1	B-Device
.	O
</s>
<s>
However	O
,	O
this	O
workstation	B-Device
is	O
unrelated	O
in	O
hardware	O
to	O
the	O
3B	B-Device
line	O
,	O
and	O
is	O
based	O
on	O
the	O
Motorola	B-Device
68010	I-Device
microprocessor	O
.	O
</s>
<s>
It	O
runs	O
a	O
derivative	O
of	O
Unix	B-Application
System	I-Application
V	O
Release	O
2	O
by	O
Convergent	O
Technologies	O
.	O
</s>
