<s>
A	O
KVM	O
is	O
a	O
computer	O
input/output	O
device	O
offering	O
the	O
combination	O
of	O
a	O
keyboard	B-Device
,	O
video	B-Device
monitor	I-Device
and	O
mouse	B-Device
(	O
pointing	B-Device
device	I-Device
)	O
.	O
</s>
<s>
They	O
are	O
typically	O
constructed	O
to	O
fit	O
into	O
a	O
19-inch	B-Application
rack	I-Application
although	O
there	O
are	O
manufacturers	O
who	O
offer	O
a	O
KVM	O
that	O
can	O
be	O
mounted	O
to	O
a	O
flat	O
surface	O
such	O
as	O
a	O
control	O
console	O
.	O
</s>
<s>
KVMs	O
did	O
not	O
exist	O
until	O
the	O
advent	O
of	O
the	O
LCD	O
computer	B-Device
monitor	I-Device
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
the	O
KVM	O
,	O
there	O
existed	O
rack-mounted	B-Application
CRT	B-Device
monitors	I-Device
and	O
separate	O
rack-mounted	B-Application
keyboards	B-Device
and	O
mice	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
the	O
LCD	O
computer	B-Device
monitor	I-Device
,	O
it	O
became	O
possible	O
to	O
combine	O
the	O
display	O
with	O
the	O
keyboard	B-Device
and	O
pointing	B-Device
device	I-Device
into	O
a	O
1U	O
,	O
2U	O
or	O
3U	O
rackmount	B-Application
form	O
factor	O
to	O
create	O
the	O
KVM	O
.	O
</s>
<s>
The	O
"	O
discriminator	O
"	O
is	O
now	O
known	O
as	O
a	O
KVM	B-Device
switch	I-Device
.	O
</s>
<s>
A	O
Clamshell	O
design	O
hinges	O
the	O
display	O
at	O
the	O
rear	O
so	O
that	O
it	O
folds	O
forward	O
over	O
the	O
keyboard	B-Device
for	O
storage	O
.	O
</s>
<s>
The	O
disadvantage	O
is	O
the	O
1U	O
thickness	O
of	O
the	O
assembly	O
limits	O
the	O
available	O
height	O
for	O
the	O
keyboard	B-Device
and	O
track-ball	O
(	O
if	O
installed	O
)	O
.	O
</s>
<s>
Some	O
KVMs	O
have	O
been	O
designed	O
to	O
fit	O
into	O
2U	O
to	O
allow	O
a	O
larger	O
track-ball	O
and	O
full-travel	O
keyboard	B-Device
to	O
be	O
installed	O
.	O
</s>
<s>
The	O
advantage	O
to	O
this	O
design	O
is	O
the	O
full	O
1U	O
height	O
can	O
be	O
used	O
for	O
keyboard	B-Device
and	O
track-ball	O
height	O
.	O
</s>
<s>
A	O
design	O
variation	O
provides	O
for	O
a	O
slim	O
profile	O
keyboard	B-Device
mounted	O
in	O
independent	O
slides	O
under	O
the	O
display	O
and	O
the	O
display	O
is	O
hinged	O
and	O
mounted	O
at	O
the	O
front	O
of	O
the	O
unit	O
.	O
</s>
<s>
This	O
allows	O
the	O
display	O
to	O
be	O
deployed	O
with	O
the	O
keyboard	B-Device
stowed	O
so	O
it	O
does	O
not	O
protrude	O
into	O
aisle	O
space	O
.	O
</s>
<s>
The	O
keyboard	B-Device
can	O
then	O
be	O
pulled	O
out	O
,	O
used	O
,	O
and	O
pushed	O
back	O
into	O
the	O
rack	O
.	O
</s>
<s>
The	O
disadvantage	O
in	O
this	O
design	O
is	O
typically	O
a	O
laptop	O
style	O
keyboard	B-Device
will	O
be	O
used	O
with	O
limited	O
keystroke	O
.	O
</s>
<s>
Input	O
signals	O
can	O
be	O
anything	O
supported	O
by	O
the	O
installed	O
LCD	O
controller	O
and	O
includes	O
,	O
but	O
is	O
not	O
limited	O
to	O
,	O
VGA	B-Protocol
,	O
DVI-D	O
,	O
DVI-I	O
,	O
HDMI	B-Protocol
,	O
Display	B-Protocol
Port	I-Protocol
,	O
Video	O
(	O
Composite	O
,	O
HD-SDI	B-Protocol
)	O
and	O
so	O
forth	O
.	O
</s>
<s>
The	O
form	O
factor	O
will	O
also	O
support	O
non-traditional	O
video	O
and	O
keyboard/mouse	O
signals	O
such	O
as	O
KVM	O
over	O
IP	O
,	O
depending	O
on	O
the	O
installed	O
control	O
circuitry	O
.	O
</s>
<s>
Output	O
from	O
the	O
keyboard	B-Device
and	O
pointing	B-Device
device	I-Device
can	O
be	O
either	O
PS/2	B-Protocol
or	O
USB	B-Protocol
,	O
or	O
both	O
,	O
or	O
can	O
be	O
routed	O
through	O
KVM	O
over	O
IP	O
or	O
similar	O
technology	O
.	O
</s>
<s>
Due	O
to	O
width	O
limitations	O
of	O
a	O
19-inch	B-Application
rack	I-Application
(	O
approximately	O
17.75	O
"	O
between	O
the	O
inside	O
rails	O
)	O
,	O
the	O
largest	O
LCD	O
to	O
be	O
incorporated	O
into	O
a	O
KVM	O
was	O
20.1	O
"	O
with	O
a	O
3:4	O
aspect	O
ratio	O
.	O
</s>
<s>
The	O
most	O
common	O
LCD	O
sizes	O
currently	O
in	O
production	O
are	O
15	O
"	O
,	O
17	O
"	O
,	O
19	B-Application
"	I-Application
and	O
20	O
"	O
.	O
</s>
<s>
A	O
wide	O
variety	O
of	O
pointing	B-Device
devices	I-Device
are	O
available	O
to	O
provide	O
mouse	B-Device
functionality	O
.	O
</s>
<s>
Many	O
keyboards	B-Device
include	O
pointing	B-Device
devices	I-Device
such	O
as	O
a	O
small	O
trackball	B-Device
,	O
touch	B-Device
pad	I-Device
,	O
joy	B-Device
stick	I-Device
,	O
or	O
pointing	B-Device
stick	I-Device
.	O
</s>
<s>
Similar	O
pointing	B-Device
devices	I-Device
are	O
available	O
as	O
stand-alone	O
modules	O
and	O
can	O
be	O
installed	O
separately	O
from	O
the	O
keyboard	B-Device
.	O
</s>
<s>
In	O
a	O
lay-flat	O
design	O
,	O
there	O
is	O
sufficient	O
height	O
in	O
a	O
1U	O
design	O
to	O
install	O
a	O
larger	O
1-1/2	O
"	O
trackball	B-Device
and	O
larger	O
trackballs	B-Device
in	O
the	O
KVMs	O
which	O
are	O
2U	O
in	O
height	O
.	O
</s>
<s>
Some	O
manufacturers	O
have	O
made	O
provision	O
for	O
using	O
a	O
true	O
mouse	B-Device
by	O
providing	O
a	O
location	O
for	O
storage	O
and	O
a	O
flat	O
surface	O
to	O
use	O
it	O
on	O
.	O
</s>
<s>
Many	O
KVMs	O
are	O
offered	O
with	O
a	O
built-in	O
KVM	B-Device
switch	I-Device
allowing	O
the	O
one	O
KVM	O
to	O
control	O
a	O
number	O
of	O
connected	O
computers	O
without	O
using	O
an	O
external	O
KVM	B-Device
switch	I-Device
.	O
</s>
<s>
The	O
KVM	B-Device
switch	I-Device
can	O
be	O
controlled	O
either	O
by	O
on-screen	O
menus	O
,	O
hot-key	O
commands	O
,	O
or	O
,	O
on	O
some	O
KVM	O
models	O
,	O
via	O
front	O
accessible	O
push	O
buttons	O
.	O
</s>
