<s>
In	O
computing	O
,	O
xterm	B-Language
is	O
the	O
standard	O
terminal	B-Application
emulator	I-Application
for	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
It	O
allows	O
users	O
to	O
run	O
programs	O
which	O
require	O
a	O
command-line	B-Application
interface	I-Application
.	O
</s>
<s>
If	O
no	O
particular	O
program	O
is	O
specified	O
,	O
xterm	B-Language
runs	O
the	O
user	O
's	O
shell	B-Application
.	O
</s>
<s>
An	O
X	B-Operating_System
display	B-Device
can	O
show	O
one	O
or	O
more	O
user	O
's	O
xterm	B-Language
windows	O
output	B-General_Concept
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Each	O
xterm	B-Language
window	O
is	O
a	O
separate	O
process	B-Operating_System
,	O
but	O
all	O
share	O
the	O
same	O
keyboard	B-Device
,	O
taking	O
turns	O
as	O
each	O
xterm	B-Language
process	B-Operating_System
acquires	O
focus	O
.	O
</s>
<s>
Normally	O
focus	O
switches	O
between	O
X	B-Operating_System
applications	O
as	O
the	O
user	O
moves	O
the	O
pointer	O
(	O
e.g.	O
,	O
a	O
mouse	O
cursor	O
)	O
about	O
the	O
screen	O
,	O
but	O
xterm	B-Language
provides	O
options	O
to	O
grab	O
focus	O
(	O
the	O
Secure	O
Keyboard	B-Device
feature	O
)	O
as	O
well	O
as	O
accept	O
input	O
events	O
sent	O
without	O
using	O
the	O
keyboard	B-Device
(	O
the	O
Allow	O
SendEvents	O
feature	O
)	O
.	O
</s>
<s>
Those	O
options	O
have	O
limitations	O
,	O
as	O
discussed	O
in	O
the	O
xterm	B-Language
manual	O
.	O
</s>
<s>
XTerm	B-Language
originated	O
prior	O
to	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
It	O
was	O
originally	O
written	O
as	O
a	O
stand-alone	O
terminal	B-Application
emulator	I-Application
for	O
the	O
VAXStation	B-Device
100	I-Device
(	O
VS100	O
)	O
by	O
Mark	O
Vandevoorde	O
,	O
a	O
student	O
of	O
Jim	O
Gettys	O
,	O
in	O
the	O
summer	O
of	O
1984	O
,	O
when	O
work	O
on	O
X	B-Operating_System
started	O
.	O
</s>
<s>
It	O
rapidly	O
became	O
clear	O
that	O
it	O
would	O
be	O
more	O
useful	O
as	O
part	O
of	O
X	B-Operating_System
than	O
as	O
a	O
standalone	O
program	O
,	O
so	O
it	O
was	O
retargeted	O
to	O
X	B-Operating_System
.	O
</s>
<s>
As	O
Gettys	O
tells	O
the	O
story	O
,	O
"	O
part	O
of	O
why	O
xterm	B-Language
's	O
internals	O
are	O
so	O
horrifying	O
is	O
that	O
it	O
was	O
originally	O
intended	O
that	O
a	O
single	O
process	B-Operating_System
be	O
able	O
to	O
drive	O
multiple	O
VS100	O
displays.	O
"	O
</s>
<s>
After	O
many	O
years	O
as	O
part	O
of	O
the	O
X	B-Operating_System
reference	O
implementation	O
,	O
around	O
1996	O
the	O
main	O
line	O
of	O
development	O
then	O
shifted	O
to	O
XFree86	B-Device
(	O
which	O
itself	O
forked	O
from	O
X11R6.3	O
)	O
,	O
and	O
it	O
is	O
now	O
maintained	O
by	O
Thomas	O
Dickey	O
.	O
</s>
<s>
Many	O
xterm	B-Language
variants	O
are	O
also	O
available	O
.	O
</s>
<s>
Most	O
terminal	B-Application
emulators	I-Application
for	O
X	B-Operating_System
started	O
as	O
variations	O
on	O
xterm	B-Language
.	O
</s>
<s>
Early	O
versions	O
emulated	O
the	O
VT102	O
and	O
Tektronix	B-General_Concept
4014	I-General_Concept
.	O
</s>
<s>
VT220	B-Device
:	O
Added	O
in	O
patch	O
24	O
.	O
</s>
<s>
Later	O
,	O
in	O
1998	O
,	O
xterm	B-Language
added	O
support	O
for	O
VT220	B-Device
features	O
,	O
such	O
as	O
extending	O
its	O
support	O
of	O
ISO-2022	O
shift	O
functions	O
to	O
provide	O
the	O
National	O
Replacement	O
Character	O
Set	O
feature	O
.	O
</s>
<s>
VT320	B-Application
:	O
Added	O
in	O
patch	O
24	O
.	O
</s>
<s>
VT420	B-Application
:	O
DECSTR	O
(	O
soft	O
terminal	O
reset	O
)	O
was	O
added	O
in	O
patch	O
34	O
.	O
</s>
<s>
In	O
2012	O
,	O
xterm	B-Language
's	O
default	O
emulation	O
was	O
changed	O
to	O
VT420	B-Application
to	O
allow	O
tmux	B-Language
to	O
assume	O
the	O
corresponding	O
left/right	O
margin	O
support	O
.	O
</s>
<s>
VT520	B-Application
:	O
Although	O
not	O
officially	O
emulated	O
,	O
parts	O
of	O
VT520	B-Application
features	O
were	O
implemented	O
.	O
</s>
<s>
As	O
with	O
most	O
X	B-Operating_System
applications	O
,	O
xterm	B-Language
can	O
be	O
customized	O
via	O
global	O
X	B-Device
resources	I-Device
files	O
(	O
e.g.	O
</s>
<s>
/usr/lib/X11/app-defaults/XTerm	O
)	O
,	O
per-user	O
resource	O
files	O
(	O
e.g.	O
</s>
<s>
~	O
/XTerm	O
,	O
~	O
/.Xresources	O
)	O
,	O
or	O
command-line	B-Application
arguments	O
.	O
</s>
<s>
Most	O
of	O
the	O
command-line	B-Application
options	O
correspond	O
to	O
resource	O
settings	O
,	O
as	O
noted	O
in	O
the	O
manual	O
page	O
.	O
</s>
<s>
While	O
the	O
name	O
of	O
the	O
program	O
is	O
xterm	B-Language
,	O
the	O
X	B-Device
resource	I-Device
class	O
is	O
XTerm	B-Language
.	O
</s>
<s>
XTerm	B-Language
normally	O
does	O
not	O
have	O
a	O
menu	O
bar	O
.	O
</s>
<s>
To	O
access	O
xterm	B-Language
's	O
three	O
menus	O
,	O
users	O
hold	O
the	O
control	O
key	O
and	O
press	O
the	O
left	O
,	O
middle	O
,	O
or	O
right	O
mouse	O
button	O
.	O
</s>
<s>
In	O
addition	O
to	O
protocols	O
used	O
in	O
commercially	O
available	O
terminal	O
machines	O
,	O
xterm	B-Language
added	O
a	O
few	O
protocols	O
that	O
have	O
been	O
adopted	O
by	O
other	O
terminal	B-Application
emulators	I-Application
,	O
such	O
as	O
:	O
</s>
<s>
Initially	O
Xterm	B-Language
supported	O
only	O
Portable	B-General_Concept
Compiled	I-General_Concept
Format	I-General_Concept
(	O
PCF	O
)	O
bitmap	O
font	O
until	O
2000	O
when	O
Xft	B-Application
library	O
was	O
introduced	O
to	O
support	O
modern	O
stroke-based	O
fonts	O
like	O
TrueType	O
.	O
</s>
