<s>
PC/104	B-Device
(	O
or	O
PC104	B-Device
)	O
is	O
a	O
family	O
of	O
embedded	B-Architecture
computer	I-Architecture
standards	O
which	O
define	O
both	O
form	O
factors	O
and	O
computer	B-General_Concept
buses	I-General_Concept
by	O
the	O
PC/104	B-Device
Consortium	O
.	O
</s>
<s>
Its	O
name	O
derives	O
from	O
the	O
104	O
pins	O
on	O
the	O
interboard	O
connector	O
(	O
ISA	B-Architecture
)	O
in	O
the	O
original	O
PC/104	B-Device
specification	O
and	O
has	O
been	O
retained	O
in	O
subsequent	O
revisions	O
,	O
despite	O
changes	O
to	O
connectors	O
.	O
</s>
<s>
PC/104	B-Device
is	O
intended	O
for	O
specialized	O
environments	O
where	O
a	O
small	O
,	O
rugged	O
computer	O
system	O
is	O
required	O
.	O
</s>
<s>
The	O
standard	O
is	O
modular	O
,	O
and	O
allows	O
consumers	O
to	O
stack	O
together	O
boards	O
from	O
a	O
variety	O
of	O
COTS	O
manufacturers	O
to	O
produce	O
a	O
customized	O
embedded	B-Architecture
system	I-Architecture
.	O
</s>
<s>
The	O
original	O
PC/104	B-Device
form	O
factor	O
is	O
somewhat	O
smaller	O
than	O
a	O
desktop	O
PC	B-Device
motherboard	I-Device
at	O
.	O
</s>
<s>
Unlike	O
other	O
popular	O
computer	O
form	O
factors	O
such	O
as	O
ATX	B-Language
,	O
which	O
rely	O
on	O
a	O
motherboard	B-Device
or	O
backplane	B-Architecture
,	O
PC/104	B-Device
boards	O
are	O
stacked	O
on	O
top	O
of	O
each	O
other	O
like	O
building	O
blocks	O
.	O
</s>
<s>
The	O
PC/104	B-Device
specification	O
defines	O
four	O
mounting	O
holes	O
at	O
the	O
corners	O
of	O
each	O
module	O
,	O
which	O
allow	O
the	O
boards	O
to	O
be	O
fastened	O
to	O
each	O
other	O
using	O
standoffs	O
.	O
</s>
<s>
A	O
typical	O
PC/104	B-Device
system	O
(	O
commonly	O
referred	O
to	O
as	O
a	O
"	O
stack	O
"	O
)	O
will	O
include	O
a	O
CPU	B-General_Concept
board	I-General_Concept
,	O
power	O
supply	O
board	O
,	O
and	O
one	O
or	O
more	O
peripheral	O
boards	O
,	O
such	O
as	O
a	O
data	B-Algorithm
acquisition	I-Algorithm
module	O
,	O
GPS	O
receiver	O
,	O
or	O
Wireless	B-Architecture
LAN	I-Architecture
controller	O
.	O
</s>
<s>
PC/104	B-Device
is	O
sometimes	O
referred	O
to	O
as	O
a	O
"	O
stackable	O
PC	O
"	O
,	O
as	O
most	O
of	O
the	O
architecture	O
derives	O
from	O
the	O
desktop	O
PC	O
.	O
</s>
<s>
The	O
majority	O
of	O
PC/104	B-Device
CPU	B-General_Concept
boards	I-General_Concept
are	O
x86	B-Operating_System
compatible	I-Operating_System
and	O
include	O
standard	O
PC	O
interfaces	O
such	O
as	O
Serial	B-Protocol
Ports	I-Protocol
,	O
USB	B-Protocol
,	O
Ethernet	O
,	O
and	O
VGA	B-Protocol
.	O
</s>
<s>
A	O
x86	B-Operating_System
PC/104	B-Device
system	O
is	O
usually	O
capable	O
of	O
standard	O
PC	O
operating	O
system	O
such	O
as	O
DOS	O
,	O
Windows	O
,	O
or	O
Linux	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
also	O
quite	O
common	O
to	O
use	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
such	O
as	O
VxWorks	B-Operating_System
.	O
</s>
<s>
The	O
PC/104	B-Device
bus	O
and	O
form	O
factor	O
was	O
originally	O
devised	O
by	O
Ampro	O
in	O
1987	O
(	O
led	O
by	O
CTO	O
Rick	O
Lehrbaum	O
)	O
,	O
and	O
later	O
standardized	O
by	O
the	O
PC/104	B-Device
Consortium	O
in	O
1992	O
.	O
</s>
<s>
An	O
IEEE	O
standard	O
corresponding	O
to	O
PC/104	B-Device
was	O
drafted	O
as	O
IEEE	O
P996.1	O
,	O
but	O
never	O
ratified	O
.	O
</s>
<s>
In	O
1997	O
,	O
the	O
PC/104	B-Device
Consortium	O
introduced	O
a	O
newer	O
standard	O
based	O
on	O
the	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
A	O
PCI	B-Protocol
Express-based	O
standard	O
was	O
introduced	O
in	O
2008	O
.	O
</s>
<s>
PC/104	B-Device
-related	O
specifications	O
are	O
controlled	O
by	O
the	O
PC/104	B-Device
Consortium	O
.	O
</s>
<s>
Membership	O
in	O
the	O
Consortium	O
is	O
not	O
required	O
to	O
design	O
and	O
manufacture	O
a	O
PC/104	B-Device
board	O
.	O
</s>
<s>
The	O
specifications	O
released	O
by	O
the	O
PC/104	B-Device
Consortium	O
define	O
multiple	O
of	O
Bus	O
Structures	O
(	O
ISA	B-Architecture
,	O
PCI	B-Protocol
,	O
PCI	B-Protocol
Express	O
)	O
and	O
Form	O
Factors	O
(	O
104	O
,	O
EBX	O
,	O
EPIC	B-Device
)	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
find	O
one	O
of	O
the	O
PC/104	B-Device
stackable	O
expansion	O
buses	O
on	O
a	O
number	O
of	O
different	O
form	O
factors	O
.	O
</s>
<s>
While	O
most	O
commercially	O
available	O
products	O
using	O
the	O
Bus	O
Structures	O
will	O
comply	O
with	O
the	O
Form	O
Factors	O
listed	O
below	O
,	O
it	O
is	O
possible	O
for	O
a	O
non-standard	O
or	O
proprietary	O
form	O
factor	O
to	O
incorporate	O
one	O
of	O
the	O
PC/104	B-Device
Bus	O
Structures	O
for	O
expandability	O
.	O
</s>
<s>
Note	O
the	O
term	O
"	O
PC/104	B-Device
"	O
is	O
often	O
used	O
interchangeably	O
to	O
refer	O
to	O
either	O
the	O
Bus	O
Structure	O
or	O
Form	O
Factor	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
product	O
datasheet	O
may	O
refer	O
to	O
a	O
board	O
as	O
"	O
PC/104	B-Device
"	O
due	O
to	O
its	O
size	O
and	O
shape	O
when	O
it	O
in	O
fact	O
has	O
a	O
PCI-104	B-Device
expansion	O
bus	O
.	O
</s>
<s>
The	O
PC/104	B-Device
Consortium	O
specifications	O
define	O
a	O
variety	O
a	O
computer	B-General_Concept
buses	I-General_Concept
,	O
all	O
of	O
which	O
derive	O
from	O
the	O
ISA	B-Architecture
,	O
PCI	B-Protocol
,	O
and	O
PCI	B-Protocol
Express	O
buses	O
found	O
in	O
a	O
desktop	O
PC	O
.	O
</s>
<s>
The	O
original	O
PC/104	B-Device
bus	O
derives	O
from	O
the	O
ISA	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
It	O
includes	O
all	O
the	O
signals	O
found	O
on	O
the	O
ISA	B-Architecture
bus	I-Architecture
,	O
with	O
additional	O
ground	O
pins	O
added	O
to	O
ensure	O
bus	O
integrity	O
.	O
</s>
<s>
Signal	O
timing	O
and	O
voltage	O
levels	O
are	O
identical	O
to	O
the	O
ISA	B-Architecture
bus	I-Architecture
,	O
with	O
lower	O
current	O
requirements	O
.	O
</s>
<s>
The	O
PC/104	B-Device
specification	O
defines	O
two	O
versions	O
of	O
the	O
bus	O
,	O
8-bit	O
or	O
16-bit	O
.	O
</s>
<s>
The	O
16-bit	O
version	O
corresponds	O
to	O
the	O
IBM	O
AT	O
and	O
adds	O
40	O
additional	O
pins	O
,	O
bringing	O
the	O
total	O
to	O
104	O
(	O
hence	O
the	O
name	O
"	O
PC/104	B-Device
"	O
)	O
.	O
</s>
<s>
Since	O
PC/104	B-Device
is	O
based	O
on	O
the	O
ISA	B-Architecture
bus	I-Architecture
,	O
it	O
is	O
often	O
necessary	O
to	O
set	O
the	O
Base	B-Device
Address	I-Device
,	O
IRQ	B-General_Concept
,	O
and	O
DMA	B-General_Concept
channel	I-General_Concept
when	O
installing	O
a	O
peripheral	O
board	O
.	O
</s>
<s>
This	O
is	O
usually	O
accomplished	O
via	O
the	O
use	O
of	O
jumpers	B-Device
or	O
DIP	O
switches	O
on	O
the	O
peripheral	O
board	O
.	O
</s>
<s>
The	O
PC/104	B-Device
-Plus	O
standard	O
adds	O
support	O
for	O
the	O
PCI	B-Protocol
bus	I-Protocol
,	O
in	O
addition	O
to	O
the	O
ISA	B-Architecture
bus	I-Architecture
of	O
the	O
PC/104	B-Device
standard	O
.	O
</s>
<s>
The	O
name	O
is	O
derived	O
from	O
its	O
origin	O
:	O
a	O
PC/104	B-Device
-Plus	O
module	O
has	O
a	O
PC/104	B-Device
connector	O
(	O
ISA	B-Architecture
)	O
plus	O
a	O
PCI	B-Protocol
connector	O
.	O
</s>
<s>
The	O
standard	O
defines	O
a	O
120-pin	O
connector	O
for	O
the	O
PCI	B-Protocol
bus	I-Protocol
,	O
located	O
on	O
the	O
opposite	O
side	O
of	O
the	O
board	O
from	O
the	O
PC/104	B-Device
connector	O
.	O
</s>
<s>
PC/104	B-Device
-Plus	O
CPU	B-General_Concept
boards	I-General_Concept
provide	O
active	O
communication	O
on	O
both	O
buses	O
,	O
and	O
are	O
capable	O
of	O
communicating	O
with	O
both	O
ISA	B-Architecture
and	O
PCI	B-Protocol
peripheral	O
cards	O
.	O
</s>
<s>
On	O
PC/104	B-Device
-Plus	O
peripheral	O
modules	O
,	O
the	O
PC/104	B-Device
connector	O
is	O
simply	O
a	O
passive	O
connector	O
for	O
stackability	O
;	O
the	O
module	O
actively	O
communicates	O
on	O
the	O
PCI	B-Protocol
bus	I-Protocol
only	O
.	O
</s>
<s>
As	O
a	O
corollary	O
,	O
a	O
PC/104	B-Device
-Plus	O
peripheral	O
module	O
may	O
not	O
be	O
used	O
with	O
a	O
PC/104	B-Device
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
However	O
,	O
a	O
PC/104	B-Device
-Plus	O
CPU	B-General_Concept
board	I-General_Concept
may	O
be	O
used	O
with	O
a	O
PC/104	B-Device
peripheral	O
module	O
.	O
</s>
<s>
Since	O
PC/104	B-Device
-Plus	O
is	O
based	O
on	O
PCI	B-Protocol
,	O
there	O
is	O
no	O
need	O
to	O
set	O
a	O
Base	B-Device
Address	I-Device
,	O
IRQ	B-General_Concept
,	O
or	O
DMA	B-General_Concept
channel	I-General_Concept
on	O
the	O
peripheral	O
boards	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
necessary	O
to	O
specify	O
the	O
PCI	B-Protocol
Slot	I-Protocol
Number	O
of	O
a	O
peripheral	O
board	O
when	O
it	O
is	O
installed	O
.	O
</s>
<s>
This	O
is	O
commonly	O
set	O
by	O
a	O
rotary	O
switch	O
,	O
DIP	O
switch	O
,	O
or	O
jumpers	B-Device
on	O
the	O
peripheral	O
board	O
.	O
</s>
<s>
Each	O
PCI	B-Protocol
peripheral	O
board	O
in	O
the	O
system	O
must	O
have	O
the	O
PCI	B-Protocol
Slot	I-Protocol
Number	O
set	O
to	O
a	O
unique	O
value	O
.	O
</s>
<s>
The	O
PCI-104	B-Device
form	O
factor	O
includes	O
the	O
PCI	B-Protocol
connector	O
,	O
but	O
not	O
the	O
PC/104	B-Device
connector	O
,	O
in	O
order	O
to	O
increase	O
the	O
available	O
board	O
real	O
estate	O
.	O
</s>
<s>
Even	O
though	O
the	O
PCI	B-Protocol
connector	O
has	O
120	O
pins	O
instead	O
of	O
104	O
,	O
the	O
established	O
name	O
was	O
kept	O
.	O
</s>
<s>
The	O
PCI	B-Protocol
connector	O
location	O
and	O
pinout	O
is	O
identical	O
to	O
PC/104	B-Device
-Plus	O
.	O
</s>
<s>
Since	O
the	O
ISA	B-Architecture
bus	I-Architecture
is	O
omitted	O
,	O
a	O
PCI-104	B-Device
board	O
is	O
incompatible	O
with	O
PC/104	B-Device
peripheral	O
module	O
.	O
</s>
<s>
However	O
,	O
PCI-104	B-Device
and	O
PC/104	B-Device
-Plus	O
are	O
compatible	O
,	O
since	O
they	O
both	O
utilize	O
the	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
Most	O
PC/104	B-Device
-Plus	O
boards	O
can	O
be	O
manufactured	O
as	O
PCI-104	B-Device
by	O
simply	O
not	O
populating	O
the	O
PC/104	B-Device
connector	O
.	O
</s>
<s>
PCI-104	B-Device
utilizes	O
the	O
same	O
PCI	B-Protocol
Slot	I-Protocol
Number	O
selection	O
scheme	O
as	O
PC/104	B-Device
-Plus	O
.	O
</s>
<s>
The	O
PCI/104	B-Device
-Express	O
specification	O
incorporates	O
the	O
PCI	B-Protocol
Express	O
bus	O
(	O
PCIe	O
)	O
in	O
addition	O
to	O
the	O
previous-generation	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
The	O
specification	O
defines	O
a	O
156-pin	O
surface	O
mount	O
connector	O
for	O
the	O
PCI	B-Protocol
Express	O
signals	O
.	O
</s>
<s>
The	O
new	O
connector	O
occupies	O
the	O
same	O
board	O
location	O
as	O
the	O
legacy	O
PC/104	B-Device
ISA	B-Architecture
connector	O
.	O
</s>
<s>
In	O
addition	O
to	O
PCI	B-Protocol
Express	O
,	O
the	O
specifications	O
also	O
defines	O
pins	O
on	O
the	O
connector	O
for	O
additional	O
modern	O
computer	B-General_Concept
buses	I-General_Concept
,	O
such	O
as	O
USB	B-Protocol
,	O
SATA	O
,	O
and	O
LPC	O
.	O
</s>
<s>
The	O
PCI/104	B-Device
-Express	O
specification	O
currently	O
defines	O
two	O
possible	O
pinouts	O
for	O
the	O
PCIe	O
connector	O
:	O
</s>
<s>
Type	O
1	O
offers	O
four	O
x1	O
PCI	B-Protocol
Express	O
links	O
,	O
two	O
USB	B-Protocol
2.0	O
ports	O
,	O
and	O
one	O
x16	O
PCIe	O
link	O
.	O
</s>
<s>
Type	O
2	O
offers	O
four	O
x1	O
PCI	B-Protocol
Express	O
links	O
,	O
two	O
USB	B-Protocol
2.0	O
ports	O
,	O
two	O
PCIe	O
x4	O
links	O
,	O
two	O
USB	B-Protocol
3.0	O
ports	O
,	O
two	O
SATA	O
ports	O
,	O
and	O
LPC	O
.	O
</s>
<s>
CPU	B-General_Concept
boards	I-General_Concept
and	O
peripherals	O
may	O
be	O
designed	O
as	O
Type	O
1	O
,	O
Type	O
2	O
,	O
or	O
Universal	O
(	O
which	O
only	O
uses	O
the	O
common	O
subset	O
of	O
signals	O
between	O
the	O
two	O
types	O
,	O
PCIe	O
x1	O
and/or	O
USB	B-Protocol
2.0	O
)	O
.	O
</s>
<s>
PCI/104	B-Device
-Express	O
products	O
introduced	O
prior	O
to	O
2011	O
will	O
be	O
either	O
Type	O
1	O
or	O
Universal	O
,	O
but	O
may	O
not	O
be	O
explicitly	O
labeled	O
as	O
such	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
CPU	B-General_Concept
board	I-General_Concept
may	O
have	O
a	O
Type	O
1	O
bottom	O
PCIe	O
connector	O
and	O
a	O
Type	O
2	O
top	O
PCIe	O
connector	O
.	O
</s>
<s>
Such	O
a	O
CPU	B-General_Concept
board	I-General_Concept
would	O
be	O
compatible	O
with	O
Type	O
1	O
and/or	O
Universal	O
peripherals	O
on	O
the	O
bottom	O
,	O
and	O
compatible	O
with	O
Type	O
2	O
and/or	O
Universal	O
peripherals	O
on	O
the	O
top	O
.	O
</s>
<s>
Similar	O
to	O
PC/104	B-Device
-Plus	O
,	O
a	O
PCI/104	B-Device
-Express	O
CPU	B-General_Concept
boards	I-General_Concept
will	O
provide	O
active	O
communication	O
on	O
both	O
PCI	B-Protocol
and	O
PCIe	O
buses	O
.	O
</s>
<s>
A	O
PC/104	B-Device
-Express	O
CPU	B-General_Concept
board	I-General_Concept
may	O
be	O
used	O
with	O
PCI-104	B-Device
and	O
PC/104	B-Device
-Plus	O
peripheral	O
modules	O
.	O
</s>
<s>
However	O
,	O
a	O
PCI/104	B-Device
-Express	O
peripheral	O
module	O
will	O
communicate	O
on	O
the	O
PCIe	O
bus	O
only	O
;	O
the	O
PCI	B-Protocol
connector	O
is	O
simply	O
a	O
pass-through	O
connector	O
for	O
stackability	O
.	O
</s>
<s>
A	O
PC/104	B-Device
-Express	O
peripheral	O
module	O
may	O
not	O
be	O
used	O
with	O
a	O
PCI-104	B-Device
or	O
PC/104	B-Device
-Plus	O
CPU	B-General_Concept
board	I-General_Concept
(	O
unless	O
an	O
ISA	B-Architecture
bridge	O
device	O
is	O
used	O
)	O
.	O
</s>
<s>
PCI/104	B-Device
-Express	O
incorporates	O
link	O
shifting	O
,	O
which	O
eliminates	O
the	O
need	O
for	O
the	O
PCI	B-Protocol
slot	I-Protocol
selection	O
switches/jumpers	O
found	O
on	O
PCI-104	B-Device
and	O
PC/104	B-Device
-Plus	O
peripherals	O
.	O
</s>
<s>
Some	O
peripheral	O
boards	O
re-populate	O
the	O
PCIe	O
links	O
,	O
which	O
allows	O
the	O
stack	O
to	O
have	O
additional	O
peripheral	O
boards	O
beyond	O
the	O
initial	O
set	O
of	O
PCI	B-Protocol
Express	O
links	O
provided	O
by	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
Link	O
repopulation	O
is	O
not	O
a	O
requirement	O
in	O
the	O
specification	O
,	O
and	O
must	O
be	O
implemented	O
on	O
the	O
peripheral	O
board	O
with	O
a	O
PCI	B-Protocol
Express	O
packet	O
switch	O
.	O
</s>
<s>
PCIe/104	O
is	O
similar	O
to	O
the	O
PCI/104	B-Device
-Express	O
standard	O
,	O
but	O
omits	O
the	O
legacy	O
PCI	B-Protocol
bus	I-Protocol
to	O
increase	O
available	O
space	O
on	O
the	O
board	O
(	O
similar	O
to	O
the	O
relationship	O
between	O
PC/104	B-Device
-Plus	O
and	O
PCI-104	B-Device
)	O
.	O
</s>
<s>
The	O
PCI	B-Protocol
Express	O
connector	O
location	O
and	O
pinout	O
options	O
the	O
same	O
as	O
PCI/104	B-Device
-Express	O
(	O
both	O
Type	O
1	O
and	O
Type	O
2	O
)	O
.	O
</s>
<s>
Because	O
the	O
PCI	B-Protocol
bus	I-Protocol
connector	O
is	O
omitted	O
,	O
a	O
PCIe/104	O
board	O
is	O
incompatible	O
with	O
PC/104	B-Device
-Plus	O
and	O
PCI-104	B-Device
systems	O
(	O
unless	O
a	O
PCIe-to-PCI	O
bridge	O
device	O
is	O
used	O
)	O
.	O
</s>
<s>
The	O
PC/104	B-Device
Consortium	O
's	O
specifications	O
cover	O
three	O
form	O
factors	O
which	O
define	O
the	O
size	O
and	O
shape	O
of	O
the	O
board	O
.	O
</s>
<s>
Some	O
PC/104	B-Device
products	O
have	O
oversized	O
PCBs	O
which	O
extended	O
into	O
the	O
I/O	O
connector	O
area	O
.	O
</s>
<s>
The	O
dimensions	O
were	O
originally	O
defined	O
in	O
the	O
PC/104	B-Device
Specification	O
,	O
and	O
as	O
a	O
result	O
the	O
form	O
factor	O
is	O
still	O
commonly	O
referred	O
to	O
as	O
"	O
PC/104	B-Device
"	O
.	O
</s>
<s>
The	O
PCI/104	B-Device
-Express	O
and	O
PCIe/104	O
Specification	O
introduced	O
the	O
"	O
104	O
"	O
name	O
to	O
distinguish	O
the	O
form	O
factor	O
from	O
the	O
legacy	O
PC/104	B-Device
bus	O
.	O
</s>
<s>
EBX	O
(	O
Embedded	B-Application
Board	I-Application
eXpandable	I-Application
)	O
is	O
a	O
single	B-Device
board	I-Device
computer	I-Device
form	O
factor	O
,	O
.	O
</s>
<s>
The	O
EBX	O
form	O
factor	O
applies	O
to	O
the	O
CPU	B-General_Concept
board	I-General_Concept
,	O
but	O
supports	O
PC/104	B-Device
form	O
factor	O
peripheral	O
boards	O
for	O
expansion	O
.	O
</s>
<s>
The	O
original	O
EBX	O
specifications	O
allowed	O
for	O
the	O
PC/104	B-Device
,	O
PC/104	B-Device
-Plus	O
,	O
and	O
PCI-104	B-Device
buses	O
.	O
</s>
<s>
EBX	O
Express	O
adds	O
the	O
PCI-104/Express	O
and	O
PCIe/104	O
buses	O
.	O
</s>
<s>
EPIC	B-Device
(	O
Embedded	O
Platform	O
for	O
Industrial	O
Computing	O
)	O
is	O
a	O
single-board	B-Device
computer	I-Device
form	O
factor	O
which	O
,	O
like	O
EBX	O
,	O
supports	O
PC/104	B-Device
peripheral	O
boards	O
but	O
is	O
smaller	O
than	O
EBX	O
at	O
.	O
</s>
<s>
It	O
allows	O
I/O	O
connections	O
to	O
be	O
implemented	O
as	O
either	O
pin	B-Protocol
headers	I-Protocol
or	O
PC-style	O
(	O
"	O
real	O
world	O
"	O
)	O
connectors	O
.	O
</s>
<s>
The	O
standard	O
provides	O
specific	O
I/O	O
zones	O
to	O
implement	O
functions	O
such	O
as	O
Ethernet	O
,	O
serial	B-Protocol
ports	I-Protocol
,	O
digital	O
and	O
analog	O
I/O	O
,	O
video	O
,	O
wireless	O
,	O
and	O
various	O
application-specific	O
interfaces	O
.	O
</s>
<s>
EPIC	B-Device
Express	O
adds	O
PCI	B-Protocol
Express	O
expandability	O
.	O
</s>
<s>
In	O
general	O
,	O
every	O
PC/104	B-Device
stack	O
will	O
contain	O
a	O
CPU	B-General_Concept
board	I-General_Concept
,	O
power	O
supply	O
board	O
,	O
and	O
one	O
or	O
more	O
peripheral	O
boards	O
.	O
</s>
<s>
The	O
maximum	O
number	O
of	O
boards	O
supported	O
by	O
a	O
PC/104	B-Device
stack	O
will	O
depend	O
on	O
the	O
which	O
buses	O
are	O
used	O
by	O
the	O
peripheral	O
boards	O
.	O
</s>
<s>
ISA	B-Architecture
Bus	I-Architecture
-	O
There	O
is	O
no	O
strict	O
limit	O
to	O
the	O
number	O
of	O
ISA	B-Architecture
boards	O
which	O
can	O
coexist	O
in	O
one	O
system	O
.	O
</s>
<s>
However	O
,	O
there	O
is	O
a	O
limited	O
number	O
of	O
Base	O
Addresses	O
,	O
IRQs	B-General_Concept
,	O
and	O
DMA	O
channels	O
which	O
may	O
become	O
a	O
limiting	O
factor	O
.	O
</s>
<s>
ISA	B-Architecture
boards	O
may	O
be	O
stacked	O
on	O
either	O
side	O
of	O
the	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
PCI	B-Protocol
Bus	I-Protocol
-	O
The	O
PC/104	B-Device
-Plus	O
and	O
PCI-104	B-Device
specifications	O
allows	O
for	O
four	O
PCI	B-Protocol
"	O
slots	O
"	O
.	O
</s>
<s>
This	O
imposes	O
a	O
hard	O
limit	O
of	O
four	O
PCI	B-Protocol
peripheral	O
boards	O
per	O
system	O
.	O
</s>
<s>
All	O
PCI	B-Protocol
peripheral	O
modules	O
must	O
connect	O
consecutively	O
on	O
one	O
side	O
of	O
the	O
controller	O
due	O
to	O
the	O
signaling	O
requirements	O
of	O
the	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
PCI	B-Protocol
Express	O
-	O
The	O
total	O
number	O
of	O
PCI	B-Protocol
Express	O
peripheral	O
boards	O
will	O
depend	O
on	O
the	O
number	O
of	O
PCIe	O
links	O
provided	O
by	O
the	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
CPU	B-General_Concept
board	I-General_Concept
provides	O
four	O
x1	O
PCIe	O
links	O
,	O
then	O
a	O
maximum	O
of	O
four	O
x1	O
PCIe	O
peripheral	O
cards	O
may	O
be	O
installed	O
.	O
</s>
<s>
PCIe	O
links	O
on	O
the	O
upper	O
side	O
of	O
the	O
CPU	B-General_Concept
board	I-General_Concept
are	O
independent	O
from	O
the	O
links	O
on	O
the	O
underside	O
.	O
</s>
<s>
Installing	O
a	O
PCIe	O
peripheral	O
under	O
the	O
CPU	B-General_Concept
board	I-General_Concept
will	O
not	O
consume	O
one	O
of	O
the	O
top	O
side	O
links	O
.	O
</s>
<s>
The	O
quantity	O
and	O
width	O
of	O
PCIe	O
links	O
available	O
may	O
vary	O
between	O
the	O
top	O
and	O
bottom	O
connectors	O
of	O
the	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
USB	B-Protocol
and	O
SATA	O
-	O
The	O
PCI/104	B-Device
-Express	O
and	O
PCIe/104	O
Specification	O
provides	O
signals	O
for	O
USB	B-Protocol
and	O
SATA	O
,	O
which	O
may	O
be	O
used	O
by	O
peripheral	O
boards	O
in	O
the	O
stack	O
.	O
</s>
<s>
Peripheral	O
which	O
use	O
USB	B-Protocol
and	O
SATA	O
will	O
be	O
limited	O
to	O
the	O
number	O
of	O
links	O
provided	O
by	O
the	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
USB	B-Protocol
peripherals	O
may	O
provide	O
link	O
repopulation	O
by	O
incorporating	O
an	O
onboard	O
USB	B-Protocol
hub	O
.	O
</s>
<s>
Regardless	O
of	O
the	O
buses	O
used	O
,	O
the	O
maximum	O
number	O
of	O
boards	O
of	O
a	O
PC/104	B-Device
stack	O
may	O
be	O
limited	O
due	O
to	O
size	O
,	O
weight	O
,	O
and	O
power	O
restrictions	O
for	O
the	O
target	O
application	O
.	O
</s>
<s>
When	O
stacking	O
PC/104	B-Device
boards	O
together	O
,	O
mechanical	O
interference	O
between	O
adjacent	O
boards	O
is	O
a	O
concern	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
PC/104	B-Device
-Plus	O
board	O
is	O
stacked	O
on	O
top	O
of	O
a	O
PC/104	B-Device
board	O
,	O
it	O
is	O
possible	O
for	O
the	O
pins	O
on	O
the	O
underside	O
of	O
the	O
PCI	B-Protocol
connector	O
to	O
run	O
into	O
components	O
on	O
the	O
lower	O
board	O
.	O
</s>
<s>
Out	O
of	O
Spec	O
Components	O
and	O
Connectors	O
-	O
The	O
PC/104	B-Device
specifications	O
limit	O
the	O
height	O
of	O
components	O
and	O
connectors	O
that	O
may	O
be	O
placed	O
on	O
either	O
side	O
of	O
the	O
board	O
.	O
</s>
<s>
Heatsinks	O
-	O
The	O
standard	O
spacing	O
between	O
stacked	O
PC/104	B-Device
boards	O
is	O
0.600	O
inches	O
(	O
15.24mm	O
)	O
.	O
</s>
<s>
It	O
is	O
not	O
uncommon	O
to	O
find	O
PC/104	B-Device
CPU	B-General_Concept
boards	I-General_Concept
with	O
relatively	O
large	O
heatsinks	O
that	O
do	O
not	O
allow	O
for	O
peripheral	O
boards	O
to	O
be	O
stacked	O
above	O
it	O
.	O
</s>
<s>
Later	O
revisions	O
of	O
the	O
PCI/104	B-Device
-Express	O
and	O
PCIe/104	O
specification	O
introduced	O
an	O
optional	O
taller	O
0.866	O
inch	O
(	O
22.00mm	O
)	O
connector	O
that	O
is	O
compatible	O
with	O
the	O
traditional	O
height	O
connector	O
.	O
</s>
<s>
In	O
theory	O
,	O
PC/104	B-Device
boards	O
are	O
interoperable	O
.	O
</s>
<s>
PC/104	B-Device
Keying	O
Pins	O
the	O
PC/104	B-Device
specification	O
defines	O
two	O
keying	O
pins	O
to	O
prevent	O
misalignment	O
of	O
the	O
connector	O
.	O
</s>
<s>
However	O
,	O
some	O
vendors	O
do	O
not	O
utilize	O
keyed	O
PC/104	B-Device
connectors	O
.	O
</s>
<s>
Required	O
Power	O
Supply	O
Voltages	O
the	O
PC/104	B-Device
buses	O
provide	O
for	O
several	O
supply	O
voltages	O
( +5V	O
,	O
+	O
3.3V	O
,	O
+12V	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
a	O
CPU	B-General_Concept
board	I-General_Concept
)	O
.	O
</s>
<s>
PCI	B-Protocol
Signaling	O
Levels	O
the	O
PCI	B-Protocol
bus	I-Protocol
may	O
operate	O
at	O
+	O
3.3V	O
or	O
+5V	O
signaling	O
levels	O
.	O
</s>
<s>
PCI	B-Protocol
VIO	O
Line	O
the	O
VIO	O
signal	O
on	O
the	O
PCI	B-Protocol
bus	I-Protocol
is	O
supposed	O
to	O
be	O
driven	O
by	O
the	O
CPU	B-General_Concept
board	I-General_Concept
.	O
</s>
<s>
However	O
,	O
some	O
peripheral	O
boards	O
and	O
power	O
supplies	O
drive	O
this	O
signal	O
(	O
in	O
violation	O
of	O
the	O
PCI	B-Protocol
specification	O
)	O
.	O
</s>
<s>
ISA	B-Architecture
Bus	I-Architecture
with	O
modern	O
chipsets	O
the	O
legacy	O
ISA	B-Architecture
bus	I-Architecture
has	O
been	O
omitted	O
from	O
modern	O
chipsets	O
.	O
</s>
<s>
Newer	O
CPU	B-General_Concept
boards	I-General_Concept
that	O
provide	O
an	O
ISA	B-Architecture
bus	I-Architecture
often	O
do	O
so	O
by	O
utilizing	O
an	O
ISA	B-Architecture
bridge	O
chip	O
(	O
either	O
PCI-to-ISA	O
or	O
LPC-to-ISA	O
)	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
the	O
ISA	B-Architecture
bus	I-Architecture
is	O
not	O
fully	O
implemented	O
,	O
and	O
compatibility	O
issues	O
may	O
appear	O
.	O
</s>
<s>
4	O
Bus	O
Masters	O
the	O
PC/104	B-Device
-Plus	O
and	O
PCI-104	B-Device
specifications	O
did	O
not	O
originally	O
allow	O
for	O
4	O
sets	O
of	O
Grant/Request	O
pairs	O
on	O
the	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
However	O
,	O
older	O
boards	O
may	O
have	O
issue	O
using	O
DMA	O
in	O
the	O
3rd	O
or	O
4th	O
PCI	B-Protocol
slot	I-Protocol
position	O
.	O
</s>
<s>
The	O
majority	O
of	O
PC/104	B-Device
CPU	B-General_Concept
boards	I-General_Concept
are	O
x86	B-Operating_System
compatible	I-Operating_System
,	O
and	O
are	O
capable	O
of	O
running	O
commercially	O
available	O
off-the-shelf	O
PC	O
software	O
without	O
modification	O
.	O
</s>
<s>
The	O
standard	O
PC	O
I/O	O
interfaces	O
of	O
a	O
PC/104	B-Device
system	O
(	O
Serial	B-Protocol
Ports	I-Protocol
,	O
USB	B-Protocol
,	O
Ethernet	O
,	O
VGA	B-Protocol
,	O
etc	O
.	O
)	O
</s>
<s>
are	O
typically	O
supported	O
via	O
the	O
native	O
drivers	B-Application
built	O
into	O
the	O
operating	O
system	O
.	O
</s>
<s>
Certain	O
peripheral	O
boards	O
,	O
such	O
as	O
data	B-Algorithm
acquisition	I-Algorithm
may	O
require	O
special	O
drivers	B-Application
from	O
the	O
board	O
manufacturer	O
.	O
</s>
<s>
From	O
a	O
software	O
development	O
perspective	O
,	O
there	O
is	O
little	O
difference	O
between	O
compiling	O
software	O
for	O
a	O
desktop	O
PC	O
or	O
compiling	O
for	O
an	O
x86	B-Operating_System
PC/104	B-Device
stack	O
.	O
</s>
<s>
Software	O
can	O
be	O
developed	O
using	O
standard	O
x86	B-Operating_System
compilers	O
(	O
e.g.	O
</s>
<s>
Visual	O
Studio	O
if	O
the	O
PC/104	B-Device
system	O
is	O
running	O
Windows	O
)	O
.	O
</s>
<s>
There	O
is	O
typically	O
no	O
need	O
for	O
specialized	O
development	O
tools	O
,	O
such	O
as	O
cross	B-Application
compilers	I-Application
,	O
Board	B-Operating_System
Support	I-Operating_System
Packages	I-Operating_System
,	O
or	O
JTAG	O
debuggers	O
.	O
</s>
<s>
This	O
is	O
a	O
significant	O
departure	O
from	O
non-x86	O
embedded	B-Architecture
system	I-Architecture
platforms	O
,	O
which	O
often	O
require	O
a	O
development	O
toolchain	O
from	O
the	O
board	O
manufacturer	O
.	O
</s>
<s>
Non-x86	O
PC/104	B-Device
CPU	B-General_Concept
boards	I-General_Concept
based	O
on	O
ARM	B-Architecture
or	O
PowerPC	B-Architecture
are	O
also	O
commercially	O
available	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
a	O
Board	B-Operating_System
Support	I-Operating_System
Package	I-Operating_System
is	O
usually	O
provided	O
by	O
the	O
manufacturer	O
for	O
the	O
supported	O
operating	O
system(s )	O
.	O
</s>
<s>
When	O
printing	O
"	O
PC/104	B-Device
"	O
or	O
its	O
variants	O
,	O
it	O
is	O
common	O
for	O
the	O
forward	O
slash	O
or	O
dashes	O
to	O
be	O
omitted	O
.	O
</s>
<s>
PC/104	B-Device
may	O
be	O
abbreviated	O
as	O
PC104	B-Device
,	O
PCI-104	B-Device
abbreviated	O
as	O
PCI104	B-Device
,	O
etc	O
.	O
</s>
<s>
Additionally	O
,	O
it	O
is	O
common	O
for	O
PC/104	B-Device
-Plus	O
to	O
be	O
abbreviated	O
with	O
a	O
plus	O
sign	O
(	O
e.g.	O
</s>
<s>
PC104+	O
)	O
.	O
</s>
<s>
Such	O
abbreviations	O
are	O
not	O
officially	O
recognized	O
in	O
any	O
PC/104	B-Device
Consortium	O
specifications	O
or	O
literature	O
,	O
however	O
they	O
have	O
been	O
in	O
use	O
for	O
some	O
time	O
.	O
</s>
<s>
PC/104	B-Device
systems	O
often	O
require	O
small	O
,	O
non-volatile	O
storage	O
,	O
such	O
as	O
that	O
afforded	O
by	O
compact	B-Device
flash	I-Device
and	O
solid	B-Device
state	I-Device
disk	I-Device
(	O
SSD	B-Device
)	O
devices	O
.	O
</s>
<s>
Additionally	O
,	O
their	O
compactness	O
and	O
physical	O
durability	O
is	O
often	O
better-suited	O
to	O
rugged	O
PC/104	B-Device
applications	O
;	O
the	O
size	O
of	O
magnetic	O
hard	O
drives	O
can	O
be	O
cumbersome	O
and	O
their	O
many	O
delicate	O
parts	O
are	O
more	O
susceptible	O
to	O
failure	O
in	O
harsh	O
environments	O
.	O
</s>
