<s>
TURBOchannel	B-Device
is	O
an	O
open	O
computer	B-General_Concept
bus	I-General_Concept
developed	O
by	O
DEC	O
by	O
during	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
.	O
</s>
<s>
Although	O
it	O
is	O
open	O
for	O
any	O
vendor	O
to	O
implement	O
in	O
their	O
own	O
systems	O
,	O
it	O
was	O
mostly	O
used	O
in	O
Digital	O
's	O
own	O
systems	O
such	O
as	O
the	O
MIPS-based	O
DECstation	B-Device
and	O
DECsystem	B-Device
systems	O
,	O
in	O
the	O
VAXstation	O
4000	O
,	O
and	O
in	O
the	O
Alpha-based	O
DEC	B-Device
3000	I-Device
AXP	I-Device
.	O
</s>
<s>
Digital	O
abandoned	O
the	O
use	O
of	O
TURBOchannel	B-Device
in	O
favor	O
of	O
the	O
EISA	B-Device
and	O
PCI	B-Protocol
buses	O
in	O
late	O
1994	O
,	O
with	O
the	O
introduction	O
of	O
their	O
AlphaStation	B-Device
and	O
AlphaServer	B-Device
systems	O
.	O
</s>
<s>
TURBOchannel	B-Device
was	O
developed	O
in	O
the	O
late	O
1980s	O
by	O
Digital	O
and	O
was	O
continuously	O
revised	O
through	O
the	O
early	O
1990s	O
by	O
the	O
TURBOchannel	B-Device
Industry	O
Group	O
,	O
an	O
industry	O
group	O
set	O
up	O
by	O
Digital	O
to	O
develop	O
promote	O
the	O
bus	O
.	O
</s>
<s>
TURBOchannel	B-Device
has	O
been	O
an	O
open	O
bus	O
from	O
the	O
beginning	O
,	O
the	O
specification	O
was	O
publicly	O
available	O
at	O
an	O
initial	O
purchase	O
cost	O
for	O
the	O
reproduction	O
of	O
material	O
for	O
third-party	O
implementation	O
,	O
as	O
were	O
the	O
mechanical	O
specifications	O
,	O
for	O
both	O
implementation	O
in	O
both	O
systems	O
and	O
in	O
options	O
.	O
</s>
<s>
TURBOchannel	B-Device
was	O
selected	O
by	O
the	O
failed	O
ACE	O
(	O
Advanced	B-Device
Computing	I-Device
Environment	I-Device
)	O
for	O
use	O
as	O
the	O
industry	O
standard	O
bus	O
in	O
ARC	B-Device
(	O
Advanced	B-Device
RISC	I-Device
Computing	I-Device
)	O
compliant	O
machines	O
.	O
</s>
<s>
Digital	O
initially	O
expected	O
TURBOchannel	B-Device
to	O
gain	O
widespeard	O
industry	O
acceptance	O
due	O
to	O
its	O
status	O
as	O
an	O
ARC	B-Device
standard	O
,	O
although	O
ultimately	O
Digital	O
was	O
the	O
only	O
major	O
user	O
of	O
the	O
TURBOchannel	B-Device
in	O
their	O
own	O
DEC	B-Device
3000	I-Device
AXP	I-Device
,	O
DECstation	B-Device
5000	I-Device
Series	I-Device
,	O
DECsystem	B-Device
and	O
VAXstation	O
4000	O
systems	O
.	O
</s>
<s>
While	O
no	O
third	O
parties	O
implemented	O
TURBOchannel	B-Device
in	O
systems	O
,	O
they	O
did	O
implement	O
numerous	O
TURBOchannel	B-Device
option	O
modules	O
for	O
Digital	O
's	O
systems	O
.	O
</s>
<s>
Although	O
the	O
main	O
developer	O
and	O
promoter	O
of	O
TURBOchannel	B-Device
was	O
the	O
TURBOchannel	B-Device
Industry	O
Group	O
,	O
Digital	O
's	O
TRI/ADD	O
Program	O
,	O
an	O
initiative	O
to	O
provide	O
technical	O
and	O
marketing	O
support	O
to	O
third	O
parties	O
implementing	O
peripherals	O
based	O
on	O
open	O
interfaces	O
such	O
as	O
FutureBus+	O
,	O
SCSI	O
,	O
VME	O
and	O
TURBOchannel	B-Device
for	O
Digital	O
's	O
systems	O
,	O
was	O
also	O
involved	O
in	O
promoting	O
TURBOchannel	B-Device
implementation	O
and	O
sales	O
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
Digital	O
expected	O
the	O
TURBOchannel	B-Device
bus	O
to	O
face	O
serious	O
competition	O
from	O
other	O
buses	O
from	O
other	O
vendors	O
such	O
as	O
HP	O
,	O
Sun	O
and	O
IBM	O
,	O
and	O
therefore	O
it	O
announced	O
that	O
it	O
intended	O
to	O
update	O
the	O
existing	O
TURBOchannel	B-Device
specification	O
to	O
permit	O
it	O
to	O
transfer	O
up	O
to	O
200	O
MB/s	O
,	O
using	O
similar	O
hardware	O
.	O
</s>
<s>
This	O
upgrade	O
to	O
the	O
protocol	O
was	O
to	O
be	O
backwards	O
compatible	O
,	O
but	O
Digital	O
later	O
canceled	O
the	O
intended	O
update	O
and	O
TURBOchannel	B-Device
itself	O
towards	O
the	O
end	O
of	O
1994	O
once	O
it	O
became	O
clear	O
that	O
PCI	B-Protocol
had	O
become	O
dominant	O
.	O
</s>
<s>
TURBOchannel	B-Device
is	O
a	O
32-bit	O
address	O
and	O
data	O
multiplexed	B-Architecture
bus	O
,	O
clocked	O
at	O
frequencies	O
between	O
12.5	O
and	O
25MHz	O
,	O
with	O
a	O
maximum	O
theoretical	O
usable	O
bandwidth	O
of	O
90	O
MB/s	O
.	O
</s>
<s>
The	O
firmware	O
contained	O
within	O
TURBOchannel	B-Device
cards	O
is	O
MIPS	B-Device
machine	B-Language
code	I-Language
,	O
a	O
remnant	O
of	O
the	O
bus	O
 '	O
original	O
use	O
in	O
MIPS-based	O
systems	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
later	O
systems	O
that	O
use	O
this	O
bus	O
such	O
as	O
the	O
Alpha-based	O
DEC	B-Device
3000	I-Device
AXP	I-Device
use	O
an	O
emulator	B-Application
contained	O
in	O
its	O
system	O
firmware	O
to	O
properly	O
initialize	O
them	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
is	O
a	O
synchronous	O
,	O
asymmetrical	O
I/O	O
channel	O
.	O
</s>
<s>
A	O
simple	O
protocol	O
is	O
used	O
to	O
make	O
TURBOchannel	B-Device
efficient	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
bus	O
does	O
not	O
permit	O
bus	O
mastering	O
,	O
if	O
a	O
TURBOchannel	B-Device
connected	O
device	O
wishes	O
to	O
communicate	O
with	O
another	O
,	O
it	O
must	O
first	O
transfer	O
this	O
information	O
to	O
the	O
memory	O
so	O
the	O
other	O
device	O
can	O
read	O
it	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
protocol	O
specifies	O
that	O
each	O
option	O
has	O
its	O
own	O
physical	O
address	O
space	O
.	O
</s>
<s>
Digital	O
's	O
own	O
systems	O
use	O
anywhere	O
from	O
4	O
MB	O
(	O
for	O
early	O
DECstation	B-Device
5000s	O
)	O
to	O
128	O
MB	O
in	O
high-end	O
DEC	B-Device
3000	I-Device
AXP	I-Device
models	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
bus	O
uses	O
a	O
32-bit	O
data	O
and	O
address	O
multiplexed	B-Architecture
bus	O
for	O
transferring	O
data	O
and	O
addresses	O
.	O
</s>
<s>
Every	O
TURBOchannel	B-Device
option	O
slot	O
has	O
its	O
own	O
set	O
of	O
seven	O
point-to-point	O
control	O
lines	O
and	O
five	O
lines	O
for	O
universal	O
control	O
and	O
arbitration	O
.	O
</s>
<s>
The	O
point-to-point	O
control	O
lines	O
are	O
connected	O
directly	O
to	O
the	O
TURBOchannel	B-Device
interface	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
interface	O
was	O
not	O
defined	O
in	O
the	O
TURBOchannel	B-Device
specification	O
,	O
although	O
Digital	O
introduced	O
three	O
possible	O
schemes	O
and	O
an	O
example	O
ASIC	O
.	O
</s>
<s>
TURBOchannel	B-Device
option	O
modules	O
uses	O
a	O
96-pin	O
DIN	O
connector	O
(	O
specifically	O
DIN	O
41612	O
)	O
and	O
option	O
modules	O
mounted	O
inline	O
with	O
the	O
system	O
module	O
.	O
</s>
<s>
Although	O
double	O
and	O
triple	O
width	O
options	O
use	O
more	O
than	O
one	O
TURBOchannel	B-Device
connector	O
,	O
this	O
does	O
not	O
mean	O
that	O
bandwidth	O
is	O
doubled	O
or	O
tripled	O
,	O
as	O
the	O
slots	O
are	O
still	O
sharing	O
a	O
single	O
bus	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
slot	O
supplies	O
+5	O
and	O
+12V	O
power	O
rails	O
and	O
provides	O
a	O
maximum	O
of	O
26	O
watts	O
of	O
power	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
bus	O
can	O
be	O
"	O
extended	O
"	O
by	O
the	O
TURBOchannel	B-Device
Extender	O
(	O
TcE	O
)	O
box	O
.	O
</s>
<s>
As	O
such	O
option	O
modules	O
consume	O
additional	O
space	O
and	O
slots	O
inside	O
a	O
system	O
,	O
their	O
presence	O
may	O
limit	O
the	O
number	O
or	O
even	O
prevent	O
the	O
installation	O
of	O
other	O
TURBOchannel	B-Device
option	O
modules	O
.	O
</s>
<s>
A	O
TURBOchannel	B-Device
Extender	O
box	O
is	O
used	O
to	O
reduce	O
the	O
number	O
of	O
slots	O
required	O
inside	O
a	O
system	O
for	O
double	O
and	O
triple	O
width	O
options	O
.	O
</s>
<s>
The	O
TURBOchannel	B-Device
Extender	O
box	O
contains	O
a	O
PCB	O
with	O
three	O
TURBOchannel	B-Device
slots	O
and	O
a	O
power	O
supply	O
for	O
supplying	O
the	O
required	O
power	O
to	O
the	O
slots	O
.	O
</s>
<s>
A	O
TURBOchannel	B-Device
option	O
module	O
,	O
for	O
installation	O
in	O
the	O
host	O
,	O
accompanies	O
the	O
TcE	O
box	O
.	O
</s>
<s>
What	O
the	O
option	O
module	O
is	O
doing	O
is	O
bringing	O
out	O
the	O
data	O
,	O
addressing	O
and	O
control	O
lines	O
to	O
the	O
TURBOchannel	B-Device
extender	O
box	O
.	O
</s>
