<s>
The	O
VAXBI	B-Architecture
bus	I-Architecture
(	O
VAX	B-Device
Bus	O
Interconnect	O
bus	O
)	O
is	O
a	O
computer	O
bus	O
designed	O
and	O
sold	O
by	O
the	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
of	O
Maynard	O
,	O
Massachusetts	O
.	O
</s>
<s>
The	O
bus	O
is	O
an	O
advanced	O
,	O
configuration-free	O
synchronous	O
bus	O
used	O
on	O
DEC	O
's	O
later	O
VAX	B-Device
computers	O
.	O
</s>
<s>
Like	O
the	O
Unibus	B-Device
and	O
Q-Bus	B-Architecture
before	O
it	O
,	O
it	O
uses	O
memory-mapped	B-Architecture
I/O	I-Architecture
but	O
has	O
32-bit	O
address	O
and	O
data	O
paths	O
.	O
</s>
<s>
The	O
VAXBI	B-Architecture
is	O
a	O
multiplexed	O
bus	O
with	O
fully	O
distributed	O
arbitration	O
and	O
geographic	O
addressing	O
.	O
</s>
<s>
All	O
of	O
the	O
logic	O
required	O
to	O
implement	O
a	O
VAXBI	B-Architecture
interface	O
is	O
contained	O
within	O
a	O
single	O
custom	O
integrated	O
circuit	O
(	O
the	O
"	O
BIIC	O
"	O
)	O
and	O
the	O
physical	O
layout	O
and	O
printed	O
wiring	O
board	O
layout	O
for	O
compliant	O
cards	O
is	O
tightly	O
specified	O
,	O
right	O
down	O
to	O
the	O
location	O
of	O
the	O
dual	O
amber	O
status	O
LEDs	O
that	O
are	O
required	O
.	O
</s>
<s>
The	O
portion	O
of	O
the	O
card	O
that	O
is	O
reserved	O
for	O
the	O
bus	O
interface	O
is	O
referred	O
to	O
as	O
"	O
the	O
VAXBI	B-Architecture
corner	O
"	O
.	O
</s>
<s>
VAXBI	B-Architecture
licensees	O
were	O
given	O
the	O
appropriate	O
engineering	O
drawings	O
to	O
allow	O
them	O
to	O
exactly	O
replicate	O
a	O
compliant	O
card	O
.	O
</s>
<s>
VAXBI	B-Architecture
cards	O
mount	O
into	O
backplanes	O
using	O
a	O
ZIF	B-General_Concept
connector	O
;	O
depending	O
on	O
the	O
backplane	O
design	O
,	O
cards	O
can	O
be	O
loaded	O
from	O
the	O
top	O
or	O
the	O
front	O
side	O
of	O
the	O
backplane	O
.	O
</s>
<s>
It	O
is	O
used	O
in	O
the	O
VAX	B-Device
6000	I-Device
,	O
VAX	B-Device
8000	I-Device
(	O
82xx	O
,	O
83xx	O
,	O
85xx	O
,	O
87xx	O
,	O
88xx	O
models	O
)	O
and	O
the	O
VAX	B-Device
9000	I-Device
systems	O
and	O
also	O
on	O
the	O
MIPS	B-Device
R3000	O
based	O
DECsystem	B-Device
5800	O
series	O
.	O
</s>
<s>
A	O
PDP-11	B-Device
implementation	O
(	O
the	O
PDP-11/27	O
)	O
was	O
envisioned	O
but	O
never	O
advanced	O
beyond	O
the	O
concept	O
stage	O
.	O
</s>
