<s>
A	O
terminal	B-Application
emulator	I-Application
,	O
or	O
terminal	O
application	O
,	O
is	O
a	O
computer	B-Application
program	I-Application
that	O
emulates	B-Application
a	O
video	B-General_Concept
terminal	I-General_Concept
within	O
some	O
other	O
display	O
architecture	O
.	O
</s>
<s>
Though	O
typically	O
synonymous	O
with	O
a	O
shell	B-Application
or	O
text	O
terminal	O
,	O
the	O
term	O
terminal	O
covers	O
all	O
remote	O
terminals	O
,	O
including	O
graphical	B-Application
interfaces	I-Application
.	O
</s>
<s>
A	O
terminal	B-Application
emulator	I-Application
inside	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
is	O
often	O
called	O
a	O
terminal	B-Application
window	I-Application
.	O
</s>
<s>
A	O
terminal	B-Application
window	I-Application
allows	O
the	O
user	O
access	O
to	O
a	O
text	O
terminal	O
and	O
all	O
its	O
applications	O
such	O
as	O
command-line	B-Application
interfaces	I-Application
(	O
CLI	O
)	O
and	O
text	B-Application
user	I-Application
interface	I-Application
(	O
TUI	O
)	O
applications	O
.	O
</s>
<s>
These	O
may	O
be	O
running	O
either	O
on	O
the	O
same	O
machine	O
or	O
on	O
a	O
different	O
one	O
via	O
telnet	B-Protocol
,	O
ssh	B-Protocol
,	O
dial-up	O
,	O
or	O
over	O
a	O
direct	O
serial	B-Protocol
connection	I-Protocol
.	O
</s>
<s>
On	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
it	O
is	O
common	O
to	O
have	O
one	O
or	O
more	O
terminal	B-Application
windows	I-Application
connected	O
to	O
the	O
local	O
machine	O
.	O
</s>
<s>
Terminals	O
usually	O
support	O
a	O
set	O
of	O
escape	O
sequences	O
for	O
controlling	O
color	O
,	O
cursor	B-Application
position	O
,	O
etc	O
.	O
</s>
<s>
Terminal	B-Application
emulators	I-Application
may	O
implement	O
a	O
local	B-Error_Name
echo	I-Error_Name
function	O
,	O
which	O
may	O
erroneously	O
be	O
named	O
"	O
half-duplex	O
"	O
,	O
or	O
still	O
slightly	O
incorrectly	O
"	O
echoplex	O
"	O
(	O
which	O
is	O
formally	O
an	O
error	B-Error_Name
detection	I-Error_Name
mechanism	O
rather	O
than	O
an	O
input	O
display	O
option	O
)	O
.	O
</s>
<s>
Terminal	B-Application
emulators	I-Application
may	O
implement	O
local	O
editing	O
,	O
also	O
known	O
as	O
"	O
line-at-a-time	O
mode	O
"	O
.	O
</s>
<s>
In	O
this	O
mode	O
,	O
the	O
terminal	B-Application
emulator	I-Application
only	O
sends	O
complete	O
lines	O
of	O
input	O
to	O
the	O
host	O
system	O
.	O
</s>
<s>
The	O
user	O
enters	O
and	O
edits	O
a	O
line	O
,	O
but	O
it	O
is	O
held	O
locally	O
within	O
the	O
terminal	B-Application
emulator	I-Application
as	O
it	O
is	O
being	O
edited	O
.	O
</s>
<s>
Line-at-a-time	O
mode	O
implies	O
local	B-Error_Name
echo	I-Error_Name
,	O
since	O
otherwise	O
the	O
user	O
will	O
not	O
be	O
able	O
to	O
see	O
the	O
line	O
as	O
it	O
is	O
being	O
edited	O
and	O
constructed	O
.	O
</s>
<s>
However	O
,	O
line-at-a-time	O
mode	O
is	O
independent	O
of	O
echo	B-Error_Name
mode	O
and	O
does	O
not	O
require	O
local	B-Error_Name
echo	I-Error_Name
.	O
</s>
<s>
When	O
entering	O
a	O
password	O
,	O
for	O
example	O
,	O
line-at-a-time	O
entry	O
with	O
local	O
editing	O
is	O
possible	O
,	O
but	O
local	B-Error_Name
echo	I-Error_Name
is	O
turned	O
off	O
(	O
otherwise	O
the	O
password	O
would	O
be	O
displayed	O
)	O
.	O
</s>
<s>
The	O
complexities	O
of	O
line-at-a-time	O
mode	O
are	O
exemplified	O
by	O
the	O
line-at-a-time	O
mode	O
option	O
in	O
the	O
telnet	B-Protocol
protocol	O
.	O
</s>
<s>
To	O
implement	O
it	O
correctly	O
,	O
the	O
Network	O
Virtual	O
Terminal	O
implementation	O
provided	O
by	O
the	O
terminal	B-Application
emulator	I-Application
program	O
must	O
be	O
capable	O
of	O
recognizing	O
and	O
properly	O
dealing	O
with	O
"	O
interrupt	O
"	O
and	O
"	O
abort	O
"	O
events	O
that	O
arrive	O
in	O
the	O
middle	O
of	O
locally	O
editing	O
a	O
line	O
.	O
</s>
<s>
Terminal	B-Application
emulators	I-Application
that	O
simulate	O
the	O
3270	B-Operating_System
protocol	O
are	O
available	O
for	O
most	O
operating	O
systems	O
,	O
for	O
use	O
both	O
by	O
those	O
administering	O
systems	O
such	O
as	O
the	O
z9	B-Device
,	O
as	O
well	O
as	O
those	O
using	O
the	O
corresponding	O
applications	O
such	O
as	O
CICS	B-Application
.	O
</s>
<s>
Other	O
examples	O
of	O
synchronous	O
terminals	O
include	O
the	O
IBM	B-Device
5250	I-Device
,	O
ICL	O
7561	O
,	O
Honeywell	O
Bull	O
VIP7800	O
and	O
Hewlett-Packard	O
700/92	O
.	O
</s>
<s>
Virtual	B-Application
consoles	I-Application
,	O
also	O
called	O
virtual	O
terminals	O
,	O
are	O
emulated	B-Application
text	B-General_Concept
terminals	I-General_Concept
,	O
using	O
the	O
keyboard	O
and	O
monitor	O
of	O
a	O
personal	O
computer	O
or	O
workstation	O
.	O
</s>
<s>
The	O
word	O
"	O
text	O
"	O
is	O
key	O
since	O
virtual	B-Application
consoles	I-Application
are	O
not	O
GUI	B-Application
terminals	I-Application
and	O
they	O
do	O
not	O
run	O
inside	O
a	O
graphical	B-Application
interface	I-Application
.	O
</s>
<s>
Virtual	B-Application
consoles	I-Application
are	O
found	O
on	O
most	O
Unix-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Many	O
terminal	B-Application
emulators	I-Application
have	O
been	O
developed	O
for	O
terminals	O
such	O
as	O
VT52	B-Application
,	O
VT100	B-Device
,	O
VT220	B-Device
,	O
VT320	B-Application
,	O
IBM	B-Operating_System
3270/8/9/E	I-Operating_System
,	O
IBM	B-Device
5250	I-Device
,	O
IBM	O
3179G	O
,	O
Data	O
General	O
D211	O
,	O
Hewlett-Packard	O
HP700/92	O
,	O
Sperry/Unisys	O
2000-series	O
UTS60	B-General_Concept
,	O
Burroughs/Unisys	O
A-series	O
T27/TD830/ET1100	O
,	O
ADDS	B-Device
ViewPoint	O
,	O
Sun	O
console	O
,	O
QNX	B-Operating_System
,	O
AT386	O
,	O
SCO-ANSI	O
,	O
SNI	O
97801	O
,	O
Televideo	O
,	O
and	O
Wyse	O
50/60	O
.	O
</s>
<s>
Additionally	O
,	O
programs	O
have	O
been	O
developed	O
to	O
emulate	O
other	O
terminal	B-Application
emulators	I-Application
such	O
as	O
xterm	B-Language
and	O
assorted	O
console	B-General_Concept
terminals	I-General_Concept
(	O
e.g.	O
,	O
for	O
Linux	B-Application
)	O
.	O
</s>
<s>
Finally	O
,	O
some	O
emulators	B-Application
simply	O
refer	O
to	O
a	O
standard	O
,	O
such	O
as	O
ANSI	O
.	O
</s>
<s>
Such	O
programs	O
are	O
available	O
on	O
many	O
platforms	O
ranging	O
from	O
DOS	B-Device
and	O
Unix	B-Application
to	O
Windows	B-Application
and	O
macOS	B-Application
to	O
embedded	O
operating	O
systems	O
found	O
in	O
cellphones	O
and	O
industrial	O
hardware	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
used	O
serial	B-Protocol
port	I-Protocol
devices	O
such	O
as	O
RS-232	O
ports	O
,	O
and	O
provided	O
device	B-Application
files	I-Application
for	O
them	O
.	O
</s>
<s>
With	O
terminal	B-Application
emulators	I-Application
those	O
device	B-Application
files	I-Application
are	O
emulated	B-Application
by	O
using	O
a	O
pair	O
of	O
pseudoterminal	B-Protocol
devices	O
.	O
</s>
<s>
This	O
pair	O
is	O
used	O
to	O
emulate	O
a	O
physical	O
port/connection	O
to	O
the	O
host	O
computing	O
endpoint	O
-	O
computer	O
's	O
hardware	O
provided	O
by	O
operating	O
system	O
APIs	O
,	O
some	O
other	O
software	O
like	O
rlogin	B-Application
,	O
telnet	B-Protocol
or	O
SSH	B-Protocol
or	O
else	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Linux	B-Application
systems	O
these	O
would	O
be	O
(	O
for	O
the	O
master	O
side	O
)	O
and	O
(	O
for	O
the	O
slave	O
side	O
)	O
pseudoterminal	B-Protocol
devices	O
respectively	O
.	O
</s>
<s>
There	O
are	O
also	O
special	O
virtual	B-Application
console	I-Application
files	O
like	O
/dev/console	O
.	O
</s>
<s>
In	O
text	O
mode	O
,	O
writing	O
to	O
the	O
file	O
displays	O
text	O
on	O
the	O
virtual	B-Application
console	I-Application
and	O
reading	O
from	O
the	O
file	O
returns	O
text	O
the	O
user	O
writes	O
to	O
the	O
virtual	B-Application
console	I-Application
.	O
</s>
<s>
As	O
with	O
other	O
text	B-General_Concept
terminals	I-General_Concept
,	O
there	O
are	O
also	O
special	O
escape	O
sequences	O
,	O
control	O
characters	O
and	O
functions	B-Operating_System
that	O
a	O
program	O
can	O
use	O
,	O
most	O
easily	O
via	O
a	O
library	O
such	O
as	O
ncurses	B-Language
.	O
</s>
<s>
For	O
more	O
complex	O
operations	O
,	O
the	O
programs	O
can	O
use	O
console	O
and	O
terminal	O
special	O
ioctl	B-Operating_System
system	B-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
One	O
can	O
compare	O
devices	O
using	O
the	O
patterns	O
vcs	O
(	O
"	O
virtual	B-Application
console	I-Application
screen	O
"	O
)	O
and	O
vcsa	O
(	O
"	O
virtual	B-Application
console	I-Application
screen	O
with	O
attributes	O
"	O
)	O
such	O
as	O
/dev/vcs1	O
and	O
/dev/vcsa1	O
.	O
</s>
<s>
Some	O
terminal	B-Application
emulators	I-Application
also	O
include	O
escape	O
sequences	O
for	O
configuring	O
the	O
behavior	O
of	O
the	O
terminal	O
to	O
facilitate	O
good	O
interoperation	O
between	O
the	O
terminal	O
and	O
programs	O
running	O
inside	O
of	O
it	O
,	O
for	O
example	O
to	O
configure	O
paste	B-General_Concept
bracketing	I-General_Concept
.	O
</s>
<s>
The	O
virtual	B-Application
consoles	I-Application
can	O
be	O
configured	O
in	O
the	O
file	O
/etc/inittab	O
read	O
by	O
init	B-Operating_System
--	O
typically	O
it	O
starts	O
the	O
text	O
mode	O
login	O
process	O
getty	B-Device
for	O
several	O
virtual	B-Application
consoles	I-Application
.	O
</s>
<s>
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
can	O
be	O
configured	O
in	O
/etc/inittab	O
or	O
by	O
an	O
X	B-Device
display	I-Device
manager	I-Device
.	O
</s>
<s>
A	O
number	O
of	O
Linux	B-Application
distributions	O
use	O
systemd	B-Application
instead	O
of	O
init	B-Operating_System
,	O
which	O
also	O
allows	O
virtual	B-Application
console	I-Application
configuration	O
.	O
</s>
<s>
Typical	O
Linux	B-Application
system	O
programs	O
used	O
to	O
access	O
the	O
virtual	B-Application
consoles	I-Application
include	O
:	O
</s>
<s>
The	O
program	O
startx	B-Device
starts	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
on	O
a	O
new	O
virtual	B-Application
console	I-Application
.	O
</s>
<s>
LinuxTV	B-Language
and	O
MPlayer	B-Application
etc	O
.	O
)	O
</s>
