<s>
A	O
19-inch	B-Application
rack	I-Application
is	O
a	O
standardized	O
frame	O
or	O
enclosure	O
for	O
mounting	O
multiple	O
electronic	O
equipment	O
modules	O
.	O
</s>
<s>
Common	O
uses	O
include	O
computer	B-Application
servers	I-Application
,	O
telecommunications	O
equipment	O
and	O
networking	B-Device
hardware	I-Device
,	O
audiovisual	O
production	O
gear	O
,	O
music	O
production	O
equipment	O
,	O
and	O
scientific	O
equipment	O
.	O
</s>
<s>
Equipment	O
designed	O
to	O
be	O
placed	O
in	O
a	O
rack	O
is	O
typically	O
described	O
as	O
rack-mount	B-Application
,	O
rack-mount	B-Application
instrument	O
,	O
a	O
rack-mounted	B-Application
system	O
,	O
a	O
rack-mount	B-Application
chassis	O
,	O
subrack	B-Application
,	O
rack	B-Application
cabinet	I-Application
,	O
rack-mountable	B-Application
,	O
or	O
occasionally	O
simply	O
shelf	O
.	O
</s>
<s>
The	O
industry-standard	O
rack	B-Application
cabinet	I-Application
is	O
42U	O
tall	O
;	O
however	O
,	O
45U	O
racks	O
are	O
also	O
common	O
.	O
</s>
<s>
The	O
term	O
relay	B-Application
rack	I-Application
appeared	O
first	O
in	O
the	O
world	O
of	O
telephony	O
.	O
</s>
<s>
The	O
19-inch	B-Application
rack	I-Application
format	O
with	O
rack-units	O
of	O
was	O
established	O
as	O
a	O
standard	O
by	O
AT&T	O
around	O
1922	O
in	O
order	O
to	O
reduce	O
the	O
space	O
required	O
for	O
repeater	O
and	O
termination	O
equipment	O
in	O
a	O
telephone	O
company	O
central	O
office	O
.	O
</s>
<s>
The	O
19-inch	B-Application
rack	I-Application
format	O
has	O
remained	O
constant	O
while	O
the	O
technology	O
that	O
is	O
mounted	O
within	O
it	O
has	O
changed	O
considerably	O
and	O
the	O
set	O
of	O
fields	O
to	O
which	O
racks	O
are	O
applied	O
has	O
greatly	O
expanded	O
.	O
</s>
<s>
Nineteen-inch	O
racks	O
in	O
two-post	O
or	O
four-post	O
form	O
hold	O
most	O
equipment	O
in	O
modern	O
data	B-Operating_System
centers	I-Operating_System
,	O
ISP	O
facilities	O
,	O
and	O
professionally	O
designed	O
corporate	O
server	B-Application
rooms	I-Application
.	O
</s>
<s>
Nineteen-inch	O
racks	O
are	O
also	O
often	O
used	O
to	O
house	O
professional	O
audio	O
and	O
video	O
equipment	O
,	O
including	O
amplifiers	O
,	O
effects	O
units	O
,	O
interfaces	O
,	O
headphone	B-Device
amplifiers	O
,	O
and	O
even	O
small-scale	O
audio	O
mixers	O
.	O
</s>
<s>
A	O
third	O
common	O
use	O
for	O
rack-mounted	B-Application
equipment	O
is	O
industrial	O
power	O
,	O
control	O
,	O
and	O
automation	O
hardware	O
.	O
</s>
<s>
Thus	O
,	O
a	O
1U	O
rackmount	B-Application
computer	O
is	O
not	O
tall	O
but	O
is	O
tall	O
.	O
</s>
<s>
Square-hole	O
racks	O
allow	O
boltless	O
mounting	O
,	O
such	O
that	O
the	O
rack-mount	B-Application
equipment	O
only	O
needs	O
to	O
insert	O
through	O
and	O
hook	O
down	O
into	O
the	O
lip	O
of	O
the	O
square	O
hole	O
.	O
</s>
<s>
Rack-mountable	B-Application
equipment	O
is	O
traditionally	O
mounted	O
by	O
bolting	O
or	O
clipping	O
its	O
front	O
panel	O
to	O
the	O
rack	O
.	O
</s>
<s>
Within	O
the	O
IT	O
industry	O
,	O
it	O
is	O
common	O
for	O
network/communications	O
equipment	O
to	O
have	O
multiple	O
mounting	O
positions	O
,	O
including	O
tabletop	O
and	O
wall	O
mounting	O
,	O
so	O
rack-mountable	B-Application
equipment	O
will	O
often	O
feature	O
L-brackets	O
that	O
must	O
be	O
screwed	O
or	O
bolted	O
to	O
the	O
equipment	O
prior	O
to	O
mounting	O
in	O
a	O
19-inch	B-Application
rack	I-Application
.	O
</s>
<s>
,	O
Generic	O
Requirements	O
for	O
Network	B-Device
Equipment	I-Device
in	O
the	O
Outside	O
Plant	O
(	O
OSP	O
)	O
,	O
specifies	O
the	O
usable	O
opening	O
of	O
seismic-compliant	O
19-inch	B-Application
racks	I-Application
.	O
</s>
<s>
Some	O
rack	O
slides	O
even	O
include	O
a	O
tilt	O
mechanism	O
allowing	O
easy	O
access	O
to	O
the	O
top	O
or	O
bottom	O
of	O
rack-mounted	B-Application
equipment	O
when	O
it	O
is	O
fully	O
extended	O
from	O
the	O
rack	O
.	O
</s>
<s>
Slides	O
or	O
rails	O
for	O
computers	O
and	O
other	O
data	O
processing	O
equipment	O
such	O
as	O
disk	B-General_Concept
arrays	I-General_Concept
or	O
routers	B-Protocol
often	O
need	O
to	O
be	O
purchased	O
directly	O
from	O
the	O
equipment	O
manufacturer	O
,	O
as	O
there	O
is	O
no	O
standardization	O
on	O
such	O
equipment	O
's	O
thickness	O
(	O
measurement	O
from	O
the	O
side	O
of	O
the	O
rack	O
to	O
the	O
equipment	O
)	O
or	O
means	O
for	O
mounting	O
to	O
the	O
rail	O
.	O
</s>
<s>
Computer	B-Application
servers	I-Application
designed	O
for	O
rack-mounting	O
can	O
include	O
a	O
number	O
of	O
extra	O
features	O
to	O
make	O
the	O
server	O
easy	O
to	O
use	O
in	O
the	O
rack	O
:	O
</s>
<s>
Some	O
manufacturers	O
of	O
rack-mount	B-Application
hardware	O
include	O
a	O
folding	O
cable	O
tray	O
behind	O
the	O
server	O
,	O
so	O
that	O
the	O
cables	O
are	O
held	O
into	O
a	O
neat	O
and	O
tidy	O
folded	O
channel	O
when	O
inside	O
the	O
rack	O
,	O
but	O
can	O
unfold	O
out	O
into	O
a	O
long	O
strip	O
when	O
pulled	O
out	O
of	O
the	O
rack	O
,	O
allowing	O
the	O
server	O
to	O
continue	O
to	O
be	O
plugged	O
in	O
and	O
operating	O
normally	O
even	O
while	O
fully	O
extended	O
and	O
hanging	O
in	O
mid-air	O
in	O
front	O
of	O
the	O
rack	O
.	O
</s>
<s>
Instead	O
,	O
a	O
KVM	B-Device
switch	I-Device
or	O
LOM	B-Application
software	O
is	O
used	O
to	O
share	O
a	O
single	O
keyboard/video/mouse	O
set	O
amongst	O
many	O
different	O
computers	O
.	O
</s>
<s>
Since	O
the	O
mounting	O
hole	O
arrangement	O
is	O
vertically	O
symmetric	O
,	O
it	O
is	O
possible	O
to	O
mount	O
rack-mountable	B-Application
equipment	O
upside-down	O
.	O
</s>
<s>
For	O
instance	O
,	O
most	O
optical	B-Device
disc	I-Device
players	O
will	O
not	O
work	O
upside-down	O
because	O
the	O
driving	O
motor	O
mechanism	O
does	O
not	O
grip	O
the	O
disc	O
.	O
</s>
<s>
19-inch	O
server	B-Application
racks	I-Application
can	O
vary	O
in	O
quality	O
.	O
</s>
<s>
A	O
standard	O
19-inch	O
server	B-Application
rack	I-Application
cabinet	O
is	O
typically	O
42u	O
in	O
height	O
,	O
wide	O
,	O
and	O
deep	O
.	O
</s>
<s>
Newer	O
server	B-Application
rack	I-Application
cabinets	O
come	O
with	O
adjustable	O
mounting	O
rails	O
allowing	O
the	O
user	O
to	O
place	O
the	O
rails	O
at	O
a	O
shorter	O
depth	O
if	O
needed	O
.	O
</s>
<s>
There	O
are	O
a	O
multitude	O
of	O
specialty	O
server	B-Application
racks	I-Application
including	O
soundproof	O
server	B-Application
racks	I-Application
,	O
air	O
conditioned	O
server	B-Application
racks	I-Application
,	O
NEMA-rated	O
,	O
seismic-rated	O
,	O
open	O
frame	O
,	O
narrow	O
,	O
and	O
even	O
miniature	O
19-inch	B-Application
racks	I-Application
for	O
smaller	O
applications	O
.	O
</s>
<s>
Cabinets	O
are	O
generally	O
sized	O
to	O
be	O
no	O
wider	O
than	O
the	O
standard	O
floor	O
tiles	O
used	O
in	O
most	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
<s>
Racks	O
carrying	O
telecom	O
equipment	O
like	O
routers	B-Protocol
and	O
switches	O
often	O
have	O
extra	O
width	O
to	O
accommodate	O
the	O
many	O
cables	O
on	O
the	O
sides	O
.	O
</s>
<s>
Most	O
data	B-Operating_System
centers	I-Operating_System
use	O
four-post	O
racks	O
.	O
</s>
<s>
The	O
Relay	B-Application
Racks	I-Application
name	O
comes	O
from	O
early	O
two-post	O
racks	O
which	O
housed	O
telephone	O
relay	O
and	O
switching	O
equipment	O
.	O
</s>
<s>
In	O
1965	O
,	O
a	O
durable	O
fiber-reinforced	O
plastic	O
19-inch	B-Application
rackmount	I-Application
case	O
was	O
patented	O
by	O
ECS	O
Composites	O
and	O
became	O
widely	O
used	O
in	O
military	O
and	O
commercial	O
applications	O
for	O
electronic	O
deployment	O
and	O
operation	O
.	O
</s>
<s>
Rackmount	B-Application
cases	O
are	O
also	O
constructed	O
of	O
thermo-stamped	O
composite	O
,	O
carbon	O
fiber	O
,	O
and	O
DuPont	O
's	O
Kevlar	O
for	O
military	O
and	O
commercial	O
uses	O
.	O
</s>
<s>
There	O
is	O
no	O
standard	O
for	O
airflow	O
and	O
cooling	O
of	O
rack-mounted	B-Application
equipment	O
.	O
</s>
<s>
For	O
rack-mounted	B-Application
computer	B-Application
servers	I-Application
,	O
devices	O
generally	O
intake	O
air	O
on	O
the	O
front	O
and	O
exhaust	O
on	O
the	O
rear	O
.	O
</s>
<s>
Large	O
server	B-Application
rooms	I-Application
will	O
often	O
group	O
rack	B-Application
cabinets	I-Application
together	O
so	O
that	O
racks	O
on	O
both	O
sides	O
of	O
an	O
aisle	O
are	O
either	O
front-facing	O
or	O
rear-facing	O
,	O
which	O
simplifies	O
cooling	O
by	O
supplying	O
cool	O
air	O
to	O
the	O
front	O
of	O
the	O
racks	O
and	O
collecting	O
hot	O
air	O
from	O
the	O
rear	O
of	O
the	O
racks	O
.	O
</s>
<s>
Raised	O
or	O
false	O
floor	O
cooling	O
in	O
server	B-Application
rooms	I-Application
can	O
serve	O
a	O
similar	O
purpose	O
;	O
they	O
permit	O
cooling	O
airflow	O
to	O
equipment	O
through	O
the	O
underfloor	O
space	O
to	O
the	O
underside	O
of	O
enclosed	O
rack	B-Application
cabinets	I-Application
.	O
</s>
<s>
In	O
the	O
case	O
of	O
network	B-Device
equipment	I-Device
,	O
it	O
may	O
be	O
necessary	O
to	O
unplug	O
50	O
or	O
more	O
cables	O
from	O
the	O
device	O
,	O
remove	O
the	O
device	O
from	O
the	O
rack	O
,	O
and	O
then	O
disassemble	O
the	O
device	O
chassis	O
to	O
replace	O
the	O
fans	O
.	O
</s>
<s>
Rack-mountable	B-Application
equipment	O
is	O
usually	O
designed	O
to	O
occupy	O
some	O
integer	O
number	O
of	O
U	O
.	O
</s>
<s>
Rack-mountable	B-Application
computers	O
and	O
servers	O
are	O
mostly	O
between	O
1U	O
and	O
4U	O
high	O
.	O
</s>
<s>
A	O
blade	B-Architecture
server	I-Architecture
enclosure	O
might	O
require	O
10U	O
.	O
</s>
<s>
Many	O
wall-mounted	O
enclosures	O
for	O
industrial	O
equipment	O
use	O
19-inch	B-Application
racks	I-Application
.	O
</s>
<s>
Some	O
telecommunications	O
and	O
networking	B-Device
equipment	I-Device
is	O
available	O
in	O
a	O
narrower	O
10	O
"	O
format	O
with	O
the	O
same	O
unit	O
height	O
as	O
a	O
standard	O
19	B-Application
"	I-Application
-rack	O
.	O
</s>
<s>
A	O
rack	O
is	O
used	O
for	O
housing	O
telephone	O
(	O
primarily	O
)	O
,	O
computer	O
,	O
audio	O
,	O
and	O
other	O
equipment	O
though	O
is	O
less	O
common	O
than	O
the	O
19-inch	B-Application
rack	I-Application
.	O
</s>
<s>
Open	O
Rack	O
is	O
a	O
mounting	O
system	O
designed	O
by	O
Facebook	B-Application
's	O
Open	B-Operating_System
Compute	I-Operating_System
Project	I-Operating_System
that	O
has	O
the	O
same	O
outside	O
dimensions	O
as	O
typical	O
19-inch	B-Application
racks	I-Application
(	O
e.g.	O
</s>
