<s>
A	O
computer	B-Architecture
appliance	I-Architecture
is	O
a	O
computer	O
system	O
with	O
a	O
combination	O
of	O
hardware	B-Architecture
,	O
software	O
,	O
or	O
firmware	B-Application
that	O
is	O
specifically	O
designed	O
to	O
provide	O
a	O
particular	O
computing	O
resource	O
.	O
</s>
<s>
The	O
hardware	B-Architecture
and	O
software	O
are	O
delivered	O
as	O
an	O
integrated	O
product	O
and	O
may	O
even	O
be	O
pre-configured	O
before	O
delivery	O
to	O
a	O
customer	O
,	O
to	O
provide	O
a	O
turn-key	O
solution	O
for	O
a	O
particular	O
application	O
.	O
</s>
<s>
Unlike	O
general	O
purpose	O
computers	O
,	O
appliances	O
are	O
generally	O
not	O
designed	O
to	O
allow	O
the	O
customers	O
to	O
change	O
the	O
software	O
and	O
the	O
underlying	O
operating	B-General_Concept
system	I-General_Concept
,	O
or	O
to	O
flexibly	O
reconfigure	O
the	O
hardware	B-Architecture
.	O
</s>
<s>
Another	O
form	O
of	O
appliance	O
is	O
the	O
virtual	B-Application
appliance	I-Application
,	O
which	O
has	O
similar	O
functionality	O
to	O
a	O
dedicated	O
hardware	B-Architecture
appliance	I-Architecture
,	O
but	O
is	O
distributed	O
as	O
a	O
software	O
virtual	B-Architecture
machine	I-Architecture
image	O
for	O
a	O
hypervisor-equipped	O
device	O
.	O
</s>
<s>
Traditionally	O
,	O
software	B-Application
applications	I-Application
run	O
on	O
top	O
of	O
a	O
general-purpose	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
,	O
which	O
uses	O
the	O
hardware	B-Architecture
resources	O
of	O
the	O
computer	O
(	O
primarily	O
memory	O
,	O
disk	O
storage	O
,	O
processing	O
power	O
,	O
and	O
networking	O
bandwidth	O
)	O
to	O
meet	O
the	O
computing	O
needs	O
of	O
the	O
user	O
.	O
</s>
<s>
It	O
is	O
complex	O
to	O
integrate	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
applications	O
with	O
a	O
hardware	B-Architecture
platform	O
,	O
and	O
complex	O
to	O
support	O
it	O
afterwards	O
.	O
</s>
<s>
By	O
tightly	O
constraining	O
the	O
variations	O
of	O
the	O
hardware	B-Architecture
and	O
software	O
,	O
the	O
appliance	O
becomes	O
easily	O
deployable	O
,	O
and	O
can	O
be	O
used	O
without	O
nearly	O
as	O
wide	O
(	O
or	O
deep	O
)	O
IT	O
knowledge	O
.	O
</s>
<s>
In	O
all	O
forms	O
of	O
the	O
computer	B-Architecture
appliance	I-Architecture
model	O
,	O
customers	O
benefit	O
from	O
easy	O
operations	O
.	O
</s>
<s>
The	O
appliance	O
has	O
exactly	O
one	O
combination	O
of	O
hardware	B-Architecture
and	O
operating	B-General_Concept
system	I-General_Concept
and	O
application	B-Application
software	I-Application
,	O
which	O
has	O
been	O
pre-installed	O
at	O
the	O
factory	O
.	O
</s>
<s>
To	O
be	O
considered	O
an	O
appliance	O
,	O
the	O
(	O
hardware	B-Architecture
)	O
device	O
needs	O
to	O
be	O
integrated	O
with	O
software	O
,	O
and	O
both	O
are	O
supplied	O
as	O
a	O
package	O
.	O
</s>
<s>
The	O
major	O
disadvantage	O
of	O
deploying	O
a	O
computer	B-Architecture
appliance	I-Architecture
is	O
that	O
since	O
they	O
are	O
designed	O
to	O
supply	O
a	O
specific	O
resource	O
,	O
they	O
most	O
often	O
include	O
a	O
customized	O
operating	B-General_Concept
system	I-General_Concept
running	O
over	O
specialized	O
hardware	B-Architecture
,	O
neither	O
of	O
which	O
are	O
likely	O
to	O
be	O
compatible	O
with	O
the	O
other	O
systems	O
previously	O
deployed	O
.	O
</s>
<s>
One	O
may	O
believe	O
that	O
a	O
proprietary	O
embedded	O
operating	B-General_Concept
system	I-General_Concept
,	O
or	O
operating	B-General_Concept
system	I-General_Concept
within	O
an	O
application	O
,	O
can	O
make	O
the	O
appliance	O
much	O
more	O
secure	O
from	O
common	O
cyber	O
attacks	O
.	O
</s>
<s>
The	O
variety	O
of	O
computer	B-Architecture
appliances	I-Architecture
reflects	O
the	O
wide	O
range	O
of	O
computing	O
resources	O
they	O
provide	O
to	O
applications	O
.	O
</s>
<s>
Storage	O
appliances	O
provide	O
massive	O
amounts	O
of	O
storage	O
and	O
additional	O
higher	O
level	O
functionality	O
(	O
ex	O
:	O
Disk	B-General_Concept
mirroring	I-General_Concept
and	O
Data	B-General_Concept
striping	I-General_Concept
)	O
for	O
multiple	O
attached	O
systems	O
using	O
the	O
transparent	O
local	O
storage	O
area	O
networks	O
computer	O
paradigm	O
.	O
</s>
<s>
Network	B-Architecture
appliances	I-Architecture
are	O
general	O
purpose	O
routers	B-Protocol
which	O
provide	O
firewall	B-Application
protection	O
,	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
,	O
messaging	B-Application
,	O
access	O
to	O
specialized	O
networking	O
protocols	O
(	O
like	O
the	O
ebXML	B-Language
Message	O
Service	O
)	O
and	O
bandwidth	O
multiplexing	B-Architecture
for	O
the	O
multiple	O
systems	O
they	O
front-end	O
.	O
</s>
<s>
Backup	B-Protocol
and	I-Protocol
disaster	I-Protocol
recovery	I-Protocol
appliances	I-Protocol
computer	B-Architecture
appliances	I-Architecture
that	O
are	O
integrated	O
backup	B-Protocol
software	O
and	O
backup	B-Protocol
targets	O
,	O
sometimes	O
with	O
hypervisors	B-Operating_System
to	O
support	O
local	O
DR	O
of	O
protected	O
servers	O
.	O
</s>
<s>
Firewall	B-Application
-	I-Application
and	O
Security	B-Application
appliances	I-Application
computer	B-Architecture
appliances	I-Architecture
that	O
are	O
designed	O
to	O
protect	O
computer	O
networks	O
from	O
unwanted	O
traffic	O
.	O
</s>
<s>
IIoT	O
and	O
MES	B-Application
Gateway	O
appliances	O
Computer	B-Architecture
appliances	I-Architecture
that	O
are	O
designed	O
to	O
translate	O
data	O
bidirectionally	O
between	O
control	O
systems	O
and	O
enterprise	O
systems	O
.	O
</s>
<s>
Proprietary	O
,	O
embedded	O
,	O
firmware	B-Application
applications	O
running	O
on	O
the	O
appliance	O
use	O
point-to-point	O
connections	O
to	O
translate	O
data	O
between	O
field	O
devices	O
in	O
their	O
native	O
automation	B-Protocol
protocols	I-Protocol
and	O
MES	B-Application
systems	O
through	O
their	O
APIs	B-General_Concept
,	O
ODBC	B-Application
,	O
or	O
RESTful	O
interfaces	O
.	O
</s>
<s>
Software	B-Application
appliances	I-Application
a	O
software	B-Application
application	I-Application
that	O
might	O
be	O
combined	O
with	O
just	B-Operating_System
enough	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
(	O
JeOS	B-Operating_System
)	O
for	O
it	O
to	O
run	O
on	O
industry	O
standard	O
hardware	B-Architecture
or	O
in	O
a	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
essence	O
,	O
the	O
software	O
distribution	O
or	O
the	O
firmware	B-Application
that	O
is	O
running	O
a	O
computer	B-Architecture
appliance	I-Architecture
.	O
</s>
<s>
Virtual	B-Application
machine	I-Application
appliances	I-Application
consist	O
of	O
a	O
"	O
hypervisor	B-Operating_System
style	O
"	O
embedded	O
operating	B-General_Concept
system	I-General_Concept
running	O
on	O
appliance	O
hardware	B-Architecture
.	O
</s>
<s>
The	O
hypervisor	B-Operating_System
layer	O
is	O
matched	O
to	O
the	O
hardware	B-Architecture
of	O
the	O
appliance	O
,	O
and	O
cannot	O
be	O
varied	O
by	O
the	O
customer	O
,	O
but	O
the	O
customer	O
may	O
load	O
other	O
operating	B-General_Concept
systems	I-General_Concept
and	O
applications	O
onto	O
the	O
appliance	O
in	O
the	O
form	O
of	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
Aside	O
from	O
its	O
deployment	O
within	O
data	O
centers	O
,	O
many	O
computer	B-Architecture
appliances	I-Architecture
are	O
directly	O
used	O
by	O
the	O
general	O
public	O
.	O
</s>
<s>
Reduced	O
downtime	O
-	O
a	O
failed	O
appliance	O
is	O
typically	O
replaced	O
with	O
a	O
COTS	O
"	O
commercial	O
off-the-shelf	O
"	O
replacement	O
and	O
its	O
task	O
is	O
quickly	O
and	O
easily	O
reloaded	O
from	O
a	O
backup	B-Protocol
.	O
</s>
<s>
PLC	O
(	O
programmable	B-Architecture
logic	I-Architecture
controller	I-Architecture
)	O
-	O
Programmable	B-Architecture
logic	I-Architecture
controllers	I-Architecture
are	O
appliances	O
that	O
are	O
typically	O
used	O
for	O
discrete	O
control	O
and	O
offer	O
a	O
wide	O
range	O
of	O
Input	O
and	O
Output	O
options	O
.	O
</s>
<s>
Universal	B-Application
gateway	I-Application
-	O
A	O
universal	B-Application
gateway	I-Application
appliance	O
has	O
the	O
ability	O
to	O
communicate	O
with	O
a	O
variety	O
of	O
devices	O
through	O
their	O
respective	O
communication	O
protocols	O
,	O
and	O
will	O
affect	O
data	O
transactions	O
between	O
them	O
.	O
</s>
<s>
They	O
communicate	O
to	O
plant	O
floor	O
equipment	O
through	O
various	O
vendor	O
automation	B-Protocol
protocols	I-Protocol
,	O
and	O
communicate	O
to	O
business	O
systems	O
through	O
database	O
communication	O
protocols	O
such	O
as	O
JMS	O
(	O
Java	B-Language
Message	I-Language
Service	I-Language
)	O
and	O
SQL	B-Language
(	O
Structured	B-Language
Query	I-Language
Language	I-Language
)	O
.	O
</s>
<s>
There	O
are	O
several	O
design	O
patterns	O
adopted	O
by	O
computer	B-Architecture
appliance	I-Architecture
vendors	O
,	O
a	O
few	O
of	O
which	O
are	O
shown	O
below	O
.	O
</s>
<s>
Special	O
chip	O
-	O
the	O
vendor	O
builds	O
an	O
ASIC	O
,	O
without	O
any	O
separate	O
"	O
software	O
"	O
or	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Azul	O
Systems	O
 '	O
Vega	O
3	O
Java	O
Compute	O
Appliance	O
is	O
an	O
example	O
;	O
special	O
hardware	B-Architecture
modifications	O
to	O
the	O
chip	O
enable	O
Java	O
application	O
scaling	O
.	O
</s>
<s>
Special	O
software	O
kernel	O
-	O
the	O
vendor	O
uses	O
or	O
creates	O
a	O
general-purpose	O
computer	O
,	O
and	O
designs	O
a	O
new	O
operating	B-General_Concept
system	I-General_Concept
that	O
integrates	O
the	O
application	O
into	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Cisco	O
's	O
IOS	B-Protocol
is	O
an	O
example	O
;	O
the	O
Unix-like	O
operating	B-General_Concept
system	I-General_Concept
has	O
firewall	B-Application
functions	O
and	O
network/firewall	O
configuration	O
commands	O
built	O
into	O
it	O
.	O
</s>
<s>
Sometimes	O
,	O
the	O
device	O
is	O
also	O
sealed	O
,	O
so	O
the	O
consumer	O
has	O
no	O
access	O
to	O
reinstall	O
the	O
operating	B-General_Concept
system	I-General_Concept
or	O
replace	O
it	O
with	O
another	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
consumer	O
may	O
also	O
be	O
restricted	O
to	O
a	O
small	O
group	O
of	O
configuration	O
commands	O
,	O
while	O
the	O
more	O
detailed	O
and	O
lower	O
level	O
functions	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
are	O
only	O
available	O
to	O
the	O
vendor	O
.	O
</s>
<s>
Specialized	O
application	O
-	O
off-the-shelf	O
computers	O
and	O
operating	B-General_Concept
systems	I-General_Concept
are	O
used	O
,	O
but	O
the	O
user	O
interface	O
and	O
"	O
box	O
"	O
are	O
designed	O
so	O
the	O
user	O
cannot	O
access	O
anything	O
on	O
the	O
computer	O
,	O
except	O
for	O
the	O
application	O
interface	O
that	O
the	O
vendor	O
has	O
created	O
.	O
</s>
<s>
Since	O
the	O
underlying	O
computing	O
architecture	O
is	O
locked	O
down	O
and	O
essentially	O
invisible	O
,	O
it	O
becomes	O
difficult	O
to	O
discern	O
that	O
the	O
device	O
really	O
functions	O
on	O
top	O
of	O
general	O
purpose	O
hardware	B-Architecture
and	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Linux	O
,	O
and	O
BSD	B-Operating_System
to	O
a	O
lesser	O
degree	O
,	O
has	O
become	O
the	O
operating	B-General_Concept
system	I-General_Concept
of	O
choice	O
for	O
this	O
type	O
of	O
appliance	O
.	O
</s>
<s>
Recently	O
the	O
term	O
software	B-Application
appliance	I-Application
has	O
also	O
been	O
used	O
to	O
describe	O
such	O
a	O
pre-packaged	O
,	O
black-box	O
combination	O
.	O
</s>
<s>
Virtual	B-Application
appliance	I-Application
-	O
here	O
the	O
hardware	B-Architecture
itself	O
has	O
disappeared	O
entirely	O
and	O
become	O
a	O
so-called	O
virtual	B-Application
appliance	I-Application
(	O
also	O
known	O
as	O
a	O
virtual	O
software	B-Application
appliance	I-Application
)	O
using	O
any	O
one	O
of	O
a	O
number	O
of	O
virtual	B-Architecture
machine	I-Architecture
technologies	O
.	O
</s>
<s>
Within	O
this	O
virtual	B-Architecture
machine	I-Architecture
is	O
essentially	O
the	O
same	O
stack	O
of	O
software	O
plus	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
in	O
the	O
"	O
specialized	O
application	O
"	O
alternative	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
VPN	B-Application
appliance	O
might	O
contain	O
a	O
limited	O
access	O
software	O
firewall	B-Application
running	O
on	O
Linux	O
,	O
with	O
an	O
encryption	O
ASIC	O
to	O
speed	O
up	O
VPN	B-Application
access	O
.	O
</s>
<s>
Some	O
computer	B-Architecture
appliances	I-Architecture
use	O
solid	B-Device
state	I-Device
storage	I-Device
,	O
while	O
others	O
use	O
a	O
hard	O
drive	O
to	O
load	O
an	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Again	O
,	O
the	O
two	O
methods	O
might	O
be	O
mixed	O
—	O
an	O
ASIC	O
print	O
server	O
might	O
allow	O
an	O
optional	O
hard	O
drive	O
for	O
job	O
queueing	O
,	O
or	O
a	O
Linux-based	O
device	O
may	O
encode	O
Linux	O
in	O
firmware	B-Application
,	O
so	O
that	O
a	O
hard	O
drive	O
is	O
not	O
needed	O
to	O
load	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
