<s>
ACCESS.bus	B-Architecture
,	O
or	O
A.b	O
for	O
short	O
,	O
is	O
a	O
peripheral-interconnect	B-Architecture
computer	I-Architecture
bus	I-Architecture
developed	O
by	O
Philips	O
and	O
DEC	O
in	O
the	O
early	O
1990s	O
,	O
based	O
on	O
Philips	O
 '	O
I²C	O
system	O
.	O
</s>
<s>
It	O
is	O
similar	O
in	O
purpose	O
to	O
USB	B-Protocol
,	O
in	O
that	O
it	O
allows	O
low-speed	O
devices	O
to	O
be	O
added	O
or	O
removed	O
from	O
a	O
computer	O
on	O
the	O
fly	O
.	O
</s>
<s>
While	O
it	O
was	O
made	O
available	O
earlier	O
than	O
USB	B-Protocol
,	O
it	O
never	O
became	O
popular	O
as	O
USB	B-Protocol
gained	O
in	O
popularity	O
.	O
</s>
<s>
Apple	O
Computer	O
's	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
(	O
ADB	O
)	O
,	O
introduced	O
in	O
the	O
mid-1980s	O
,	O
allowed	O
all	O
sorts	O
of	O
low-speed	O
devices	O
like	O
mice	O
and	O
keyboards	O
to	O
be	O
daisy-chained	O
into	O
a	O
single	O
port	O
on	O
the	O
computer	O
,	O
greatly	O
reducing	O
the	O
number	O
of	O
ports	O
needed	O
,	O
as	O
well	O
as	O
the	O
resulting	O
cable	O
clutter	O
.	O
</s>
<s>
ADB	O
was	O
universal	O
on	O
the	O
Macintosh	B-Device
line	O
by	O
the	O
late	O
1980s	O
,	O
and	O
offered	O
a	O
clear	O
advantage	O
over	O
the	O
profusion	O
of	O
standards	O
being	O
used	O
on	O
PCs	O
.	O
</s>
<s>
An	O
industry	O
group	O
,	O
the	O
ACCESS.bus	B-Architecture
Industry	O
Group	O
,	O
or	O
ABIG	O
,	O
was	O
created	O
in	O
1993	O
to	O
control	O
the	O
development	O
of	O
the	O
standard	O
.	O
</s>
<s>
Development	O
of	O
USB	B-Protocol
began	O
the	O
next	O
year	O
,	O
in	O
1994	O
,	O
and	O
the	O
consortium	O
included	O
a	O
number	O
of	O
the	O
members	O
of	O
the	O
A.b	O
group	O
,	O
notably	O
DEC	O
and	O
Microsoft	O
.	O
</s>
<s>
A.b	O
had	O
a	O
number	O
of	O
technical	O
advantages	O
over	O
USB	B-Protocol
,	O
which	O
would	O
not	O
re-appear	O
on	O
that	O
system	O
until	O
years	O
later	O
,	O
and	O
it	O
was	O
also	O
easier	O
and	O
less	O
expensive	O
to	O
implement	O
.	O
</s>
<s>
However	O
,	O
it	O
was	O
also	O
much	O
slower	O
than	O
USB	B-Protocol
,	O
ten	O
to	O
a	O
hundred	O
times	O
.	O
</s>
<s>
USB	B-Protocol
fit	O
neatly	O
into	O
the	O
performance	O
niche	O
between	O
A.b	O
and	O
FireWire	B-Protocol
,	O
which	O
made	O
it	O
practical	O
to	O
design	O
a	O
system	O
with	O
USB	B-Protocol
alone	O
.	O
</s>
<s>
Intel	O
's	O
backing	O
was	O
another	O
deciding	O
factor	O
;	O
the	O
company	O
began	O
including	O
USB	B-Protocol
controllers	O
in	O
the	O
standard	O
motherboard	B-Device
control	O
chips	O
,	O
making	O
the	O
cost	O
of	O
implementation	O
roughly	O
that	O
of	O
the	O
connector	O
.	O
</s>
<s>
They	O
needed	O
a	O
standardized	O
bus	O
for	O
communicating	O
device	O
abilities	O
and	O
status	O
between	O
monitors	O
and	O
computers	O
,	O
and	O
selected	O
I²C	O
because	O
it	O
required	O
only	O
two	O
pins	O
;	O
by	O
re-using	O
existing	O
reserved	O
pins	O
in	O
the	O
standard	O
VGA	B-Protocol
cable	O
they	O
could	O
implement	O
a	O
complete	O
A.b	O
bus	O
(	O
including	O
power	O
)	O
.	O
</s>
<s>
A	O
number	O
of	O
monitors	O
with	O
A.b	O
connectors	O
started	O
appearing	O
in	O
the	O
mid-1990s	O
,	O
notably	O
those	O
by	O
NEC	O
,	O
but	O
this	O
was	O
at	O
about	O
the	O
same	O
time	O
USB	B-Protocol
was	O
being	O
heavily	O
promoted	O
and	O
few	O
devices	O
were	O
available	O
to	O
plug	O
into	O
them	O
,	O
mostly	O
mice	O
and	O
keyboards	O
.	O
</s>
<s>
A.b	O
is	O
a	O
physical	B-Application
layer	I-Application
definition	O
that	O
describes	O
the	O
physical	O
cabling	O
and	O
connectors	O
used	O
in	O
the	O
network	O
.	O
</s>
<s>
A	O
single	O
I²C/A.b	O
controller	O
chip	O
would	O
be	O
used	O
inside	O
the	O
machine	O
,	O
connected	O
on	O
the	O
motherboard	B-Device
to	O
internal	O
devices	O
like	O
the	O
clock	O
and	O
battery	O
power	O
monitor	O
.	O
</s>
<s>
This	O
way	O
all	O
of	O
the	O
low	O
-	O
and	O
medium-speed	O
devices	O
on	O
the	O
machine	O
would	O
be	O
driven	O
by	O
a	O
single	O
controller	O
and	O
protocol	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
Depending	O
on	O
how	O
much	O
intelligence	O
the	O
device	O
needed	O
,	O
the	O
interface	O
in	O
the	O
device	O
could	O
leave	O
almost	O
all	O
of	O
the	O
work	O
to	O
the	O
driver	B-Application
.	O
</s>
<s>
Compared	O
to	O
USB	B-Protocol
,	O
A.b	O
had	O
several	O
advantages	O
.	O
</s>
<s>
Under	O
(	O
standard	O
)	O
USB	B-Protocol
the	O
computer	O
is	O
always	O
the	O
master	O
and	O
the	O
devices	O
are	O
always	O
slaves	O
.	O
</s>
<s>
In	O
order	O
to	O
support	O
the	O
same	O
sort	O
of	O
device-to-device	O
connection	O
,	O
USB	B-Protocol
requires	O
additional	O
support	O
in	O
dual-role	O
devices	O
to	O
emulate	O
a	O
host	O
and	O
provide	O
similar	O
functionality	O
.	O
</s>
<s>
This	O
was	O
only	O
standardized	O
years	O
later	O
as	O
part	O
of	O
USB	B-Protocol
On-The-Go	O
system	O
.	O
</s>
