<s>
A	O
computer	B-General_Concept
terminal	I-General_Concept
is	O
an	O
electronic	O
or	O
electromechanical	O
hardware	B-Architecture
device	O
that	O
can	O
be	O
used	O
for	O
entering	O
data	O
into	O
,	O
and	O
transcribing	O
data	O
from	O
,	O
a	O
computer	O
or	O
a	O
computing	O
system	O
.	O
</s>
<s>
The	O
teletype	O
was	O
an	O
example	O
of	O
an	O
early-day	O
hard-copy	O
terminal	O
and	O
predated	O
the	O
use	O
of	O
a	O
computer	B-Device
screen	I-Device
by	O
decades	O
.	O
</s>
<s>
Early	O
terminals	O
were	O
inexpensive	O
devices	O
but	O
very	O
slow	O
compared	O
to	O
punched	B-Architecture
cards	I-Architecture
or	O
paper	O
tape	O
for	O
input	O
,	O
yet	O
as	O
the	O
technology	O
improved	O
and	O
video	O
displays	O
were	O
introduced	O
,	O
terminals	O
pushed	O
these	O
older	O
forms	O
of	O
interaction	O
from	O
the	O
industry	O
.	O
</s>
<s>
A	O
related	O
development	O
was	O
time-sharing	B-General_Concept
systems	I-General_Concept
,	O
which	O
evolved	O
in	O
parallel	O
and	O
made	O
up	O
for	O
any	O
inefficiencies	O
in	O
the	O
user	O
's	O
typing	O
ability	O
with	O
the	O
ability	O
to	O
support	O
multiple	O
users	O
on	O
the	O
same	O
machine	O
,	O
each	O
at	O
their	O
own	O
terminal	O
or	O
terminals	O
.	O
</s>
<s>
The	O
function	O
of	O
a	O
terminal	O
is	O
typically	O
confined	O
to	O
transcription	O
and	O
input	O
of	O
data	O
;	O
a	O
device	O
with	O
significant	O
local	O
,	O
programmable	O
data-processing	O
capability	O
may	O
be	O
called	O
a	O
"	O
smart	O
terminal	O
"	O
or	O
fat	B-Protocol
client	I-Protocol
.	O
</s>
<s>
A	O
terminal	O
that	O
depends	O
on	O
the	O
host	B-Device
computer	I-Device
for	O
its	O
processing	O
power	O
is	O
called	O
a	O
"	O
dumb	O
terminal	O
"	O
or	O
a	O
thin	B-Device
client	I-Device
.	O
</s>
<s>
A	O
personal	B-Device
computer	I-Device
can	O
run	O
terminal	B-Application
emulator	I-Application
software	B-Application
that	O
replicates	O
functions	B-Operating_System
of	O
a	O
real-world	O
terminal	O
,	O
sometimes	O
allowing	O
concurrent	O
use	O
of	O
local	O
programs	O
and	O
access	O
to	O
a	O
distant	O
terminal	B-General_Concept
host	I-General_Concept
system	O
,	O
either	O
over	O
a	O
direct	O
serial	O
connection	O
or	O
over	O
a	O
network	O
using	O
,	O
e.g.	O
,	O
SSH	B-Protocol
.	O
</s>
<s>
The	O
console	O
of	O
Konrad	O
Zuse	O
's	O
Z3	B-Device
had	O
a	O
keyboard	B-Device
in	O
1941	O
,	O
as	O
did	O
the	O
Z4	B-Device
in	O
1942	O
–	O
1945	O
.	O
</s>
<s>
In	O
1955	O
,	O
the	O
Whirlwind	B-Device
Mark	O
I	O
computer	O
was	O
the	O
first	O
computer	O
equipped	O
with	O
a	O
keyboard-printer	O
combination	O
with	O
which	O
to	O
support	O
direct	O
input	O
of	O
data	O
and	O
commands	O
and	O
output	O
of	O
results	O
.	O
</s>
<s>
The	O
device	O
was	O
a	O
Friden	B-Application
Flexowriter	I-Application
,	O
which	O
would	O
continue	O
to	O
serve	O
this	O
purpose	O
on	O
many	O
other	O
early	O
computers	O
well	O
into	O
the	O
1960s	O
.	O
</s>
<s>
Early	O
user	O
terminals	O
connected	O
to	O
computers	O
were	O
,	O
like	O
the	O
Flexowriter	B-Application
,	O
electromechanical	O
teleprinters/teletypewriters	O
(	O
TeleTYpewriter	O
,	O
TTY	O
)	O
,	O
such	O
as	O
the	O
Teletype	O
Model	O
33	O
,	O
originally	O
used	O
for	O
telegraphy	O
;	O
early	O
Teletypes	O
were	O
typically	O
configured	O
as	O
Keyboard	B-Device
Send-Receive	O
(	O
KSR	O
)	O
or	O
Automatic	O
Send-Receive	O
(	O
ASR	O
)	O
,	O
the	O
latter	O
including	O
a	O
paper	O
tape	O
reader	O
and	O
punch	O
.	O
</s>
<s>
Custom-designs	O
keyboard/printer	O
terminals	O
that	O
came	O
later	O
included	O
the	O
IBM	O
2741	O
(	O
1965	O
)	O
and	O
the	O
DECwriter	B-Application
(	O
1970	O
)	O
.	O
</s>
<s>
The	O
DECwriter	B-Application
was	O
the	O
last	O
major	O
printing-terminal	O
product	O
.	O
</s>
<s>
It	O
faded	O
away	O
after	O
1980	O
under	O
pressure	O
from	O
video	B-Device
display	I-Device
units	I-Device
(	O
VDUs	O
)	O
,	O
with	O
the	O
last	O
revision	O
(	O
the	O
DECwriter	B-Application
IV	O
of	O
1982	O
)	O
abandoning	O
the	O
classic	O
teletypewriter	O
form	O
for	O
one	O
more	O
resembling	O
a	O
desktop	O
printer	O
.	O
</s>
<s>
A	O
video	B-Device
display	I-Device
unit	I-Device
(	O
VDU	O
)	O
displays	O
information	O
on	O
a	O
screen	O
rather	O
than	O
printing	O
text	O
to	O
paper	O
and	O
typically	O
uses	O
a	O
cathode-ray	B-Device
tube	I-Device
(	O
CRT	O
)	O
.	O
</s>
<s>
VDUs	O
in	O
the	O
1950s	O
were	O
typically	O
designed	O
for	O
displaying	O
graphical	O
data	O
rather	O
than	O
text	O
and	O
were	O
used	O
in	O
,	O
e.g.	O
,	O
experimental	O
computers	O
at	O
institutions	O
like	O
MIT	O
;	O
computers	O
used	O
in	O
academia	O
,	O
government	O
and	O
business	O
,	O
sold	O
under	O
brand	O
names	O
like	O
DEC	O
,	O
ERA	O
,	O
IBM	O
and	O
UNIVAC	O
;	O
military	O
computers	O
supporting	O
specific	O
defence	O
applications	O
such	O
as	O
ballistic	B-Architecture
missile	I-Architecture
warning	I-Architecture
systems	I-Architecture
and	O
radar/air	O
defence	O
coordination	O
systems	O
like	O
BUIC	O
and	O
SAGE	B-Device
.	O
</s>
<s>
Two	O
early	O
landmarks	O
in	O
the	O
development	O
of	O
the	O
VDU	O
were	O
the	O
Univac	O
Uniscope	B-General_Concept
300	O
and	O
the	O
IBM	B-Device
2260	I-Device
,	O
both	O
in	O
1964	O
.	O
</s>
<s>
The	O
Hazeltine	B-Device
2000	I-Device
of	O
1970	O
was	O
a	O
notable	O
product	O
of	O
this	O
kind	O
.	O
</s>
<s>
The	O
Datapoint	B-Device
3300	I-Device
from	O
Computer	B-General_Concept
Terminal	I-General_Concept
Corporation	O
,	O
announced	O
in	O
1967	O
and	O
shipped	O
in	O
1969	O
,	O
was	O
a	O
character-mode	O
device	O
that	O
emulated	O
a	O
Model	B-Application
33	I-Application
Teletype	I-Application
.	O
</s>
<s>
The	O
next	O
generation	O
of	O
VDUs	O
went	O
beyond	O
teletype	O
emulation	O
with	O
an	O
addressable	O
cursor	B-Application
that	O
gave	O
them	O
the	O
ability	O
to	O
paint	O
two-dimensional	O
displays	O
on	O
the	O
screen	O
.	O
</s>
<s>
The	O
classic	O
era	O
of	O
the	O
VDU	O
began	O
in	O
the	O
early	O
1970s	O
and	O
was	O
closely	O
intertwined	O
with	O
the	O
rise	O
of	O
time	B-General_Concept
sharing	I-General_Concept
computers	I-General_Concept
.	O
</s>
<s>
Important	O
early	O
products	O
were	O
the	O
ADM-3A	B-Device
,	O
VT52	B-Application
,	O
and	O
VT100	B-Device
.	O
</s>
<s>
These	O
devices	O
used	O
no	O
CPU	B-General_Concept
,	O
instead	O
relying	O
on	O
individual	O
logic	O
gates	O
or	O
very	O
primitive	O
LSI	O
chips	O
.	O
</s>
<s>
RS-232	O
serial	B-Protocol
ports	I-Protocol
(	O
25-pin	O
,	O
ready	O
to	O
connect	O
to	O
a	O
modem	B-Application
,	O
yet	O
some	O
manufacturer-specific	O
pin	O
usage	O
extended	O
the	O
standard	O
,	O
e.g.	O
</s>
<s>
24	O
lines	O
(	O
or	O
possibly	O
25	O
–	O
sometimes	O
a	O
special	O
status	O
line	O
)	O
of	O
72	O
or	O
80	O
characters	O
of	O
text	O
(	O
80	O
was	O
the	O
same	O
as	O
IBM	O
punched	B-Architecture
cards	I-Architecture
)	O
.	O
</s>
<s>
Some	O
type	O
of	O
cursor	B-Application
that	O
can	O
be	O
positioned	O
(	O
with	O
arrow	B-Device
keys	I-Device
or	O
"	O
home	O
"	O
and	O
other	O
direct	O
cursor	B-Application
address	O
setting	O
codes	O
)	O
.	O
</s>
<s>
Implementation	O
of	O
at	O
least	O
3	O
control	O
codes	O
:	O
Carriage	O
Return	O
(	O
Ctrl-M	O
)	O
,	O
Line-Feed	O
(	O
Ctrl-J	O
)	O
,	O
and	O
Bell	O
(	O
Ctrl-G	O
)	O
,	O
but	O
usually	O
many	O
more	O
,	O
such	O
as	O
escape	O
sequences	O
to	O
provide	O
underlining	O
,	O
dim	O
or	O
reverse-video	O
character	O
highlighting	O
,	O
and	O
especially	O
to	O
clear	O
the	O
display	O
and	O
position	O
the	O
cursor	B-Application
.	O
</s>
<s>
The	O
experimental	O
era	O
of	O
serial	O
VDUs	O
culminated	O
with	O
the	O
VT100	B-Device
in	O
1978	O
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
,	O
there	O
were	O
dozens	O
of	O
manufacturers	O
of	O
terminals	O
,	O
including	O
Lear-Siegler	B-Device
,	O
ADDS	B-Device
,	O
Data	O
General	O
,	O
DEC	O
,	O
Hazeltine	O
Corporation	O
,	O
Heath/Zenith	O
,	O
Hewlett-Packard	O
,	O
IBM	O
,	O
TeleVideo	O
,	O
Volker-Craig	O
,	O
and	O
Wyse	O
,	O
many	O
of	O
which	O
had	O
incompatible	O
command	O
sequences	O
(	O
although	O
many	O
used	O
the	O
early	O
ADM-3	B-Device
as	O
a	O
starting	O
point	O
)	O
.	O
</s>
<s>
The	O
great	O
variations	O
in	O
the	O
control	O
codes	O
between	O
makers	O
gave	O
rise	O
to	O
software	B-Application
that	O
identified	O
and	O
grouped	O
terminal	O
types	O
so	O
the	O
system	O
software	B-Application
would	O
correctly	O
display	O
input	O
forms	O
using	O
the	O
appropriate	O
control	O
codes	O
;	O
In	O
Unix-like	B-Operating_System
systems	I-Operating_System
the	O
termcap	B-Application
or	O
terminfo	B-Device
files	O
,	O
the	O
stty	O
utility	O
,	O
and	O
the	O
TERM	O
environment	O
variable	O
would	O
be	O
used	O
;	O
in	O
Data	O
General	O
's	O
Business	O
BASIC	O
software	B-Application
,	O
for	O
example	O
,	O
at	O
login-time	O
a	O
sequence	O
of	O
codes	O
were	O
sent	O
to	O
the	O
terminal	O
to	O
try	O
to	O
read	O
the	O
cursor	B-Application
's	O
position	O
or	O
the	O
25th	O
line	O
's	O
contents	O
using	O
a	O
sequence	O
of	O
different	O
manufacturer	O
's	O
control	O
code	O
sequences	O
,	O
and	O
the	O
terminal-generated	O
response	O
would	O
determine	O
a	O
single-digit	O
number	O
(	O
such	O
as	O
6	O
for	O
Data	O
General	O
Dasher	O
terminals	O
,	O
4	O
for	O
ADM	O
3A/5/11/12	O
terminals	O
,	O
0	O
or	O
2	O
for	O
TTYs	O
with	O
no	O
special	O
features	O
)	O
that	O
would	O
be	O
available	O
to	O
programs	O
to	O
say	O
which	O
set	O
of	O
codes	O
to	O
use	O
.	O
</s>
<s>
Terminals	O
with	O
modest	O
color	O
capability	O
were	O
also	O
available	O
but	O
not	O
widely	O
used	O
;	O
for	O
example	O
,	O
a	O
color	O
version	O
of	O
the	O
popular	O
Wyse	O
WY50	O
,	O
the	O
WY350	O
,	O
offered	O
64	O
shades	O
on	O
each	O
character	B-Application
cell	I-Application
.	O
</s>
<s>
VDUs	O
were	O
eventually	O
displaced	O
from	O
most	O
applications	O
by	O
networked	O
personal	B-Device
computers	I-Device
,	O
at	O
first	O
slowly	O
after	O
1985	O
and	O
with	O
increasing	O
speed	O
in	O
the	O
1990s	O
.	O
</s>
<s>
However	O
,	O
they	O
had	O
a	O
lasting	O
influence	O
on	O
PCs	B-Device
.	O
</s>
<s>
The	O
keyboard	B-Device
layout	O
of	O
the	O
VT220	B-Device
terminal	O
strongly	O
influenced	O
the	O
Model	B-Device
M	I-Device
shipped	O
on	O
IBM	B-Device
PCs	I-Device
from	O
1985	O
,	O
and	O
through	O
it	O
all	O
later	O
computer	B-Device
keyboards	I-Device
.	O
</s>
<s>
Although	O
flat-panel	B-General_Concept
displays	I-General_Concept
were	O
available	O
since	O
the	O
1950s	O
,	O
cathode-ray	B-Device
tubes	I-Device
continued	O
to	O
dominate	O
the	O
market	O
until	O
the	O
personal	B-Device
computer	I-Device
had	O
made	O
serious	O
inroads	O
into	O
the	O
display	O
terminal	O
market	O
.	O
</s>
<s>
By	O
the	O
time	O
cathode-ray	B-Device
tubes	I-Device
on	O
PCs	B-Device
were	O
replaced	O
by	O
flatscreens	B-General_Concept
after	O
the	O
year	O
2000	O
,	O
the	O
hardware	B-Architecture
computer	B-General_Concept
terminal	I-General_Concept
was	O
nearly	O
obsolete	O
.	O
</s>
<s>
A	O
character-oriented	O
terminal	O
is	O
a	O
type	O
of	O
computer	B-General_Concept
terminal	I-General_Concept
that	O
communicates	O
with	O
its	O
host	B-Device
one	O
character	O
at	O
a	O
time	O
,	O
as	O
opposed	O
to	O
a	O
block-oriented	O
terminal	O
that	O
communicates	O
in	O
blocks	O
of	O
data	O
.	O
</s>
<s>
It	O
is	O
the	O
most	O
common	O
type	O
of	O
data	B-General_Concept
terminal	I-General_Concept
,	O
because	O
it	O
's	O
easy	O
to	O
implement	O
and	O
program	O
.	O
</s>
<s>
Connection	O
to	O
the	O
mainframe	B-Architecture
computer	I-Architecture
or	O
terminal	B-Device
server	I-Device
is	O
achieved	O
via	O
RS-232	O
serial	O
links	O
,	O
Ethernet	O
or	O
other	O
proprietary	O
protocols	O
.	O
</s>
<s>
but	O
do	O
not	O
have	O
the	O
ability	O
to	O
process	O
special	O
escape	O
sequences	O
that	O
perform	O
functions	B-Operating_System
such	O
as	O
clearing	O
a	O
line	O
,	O
clearing	O
the	O
screen	O
,	O
or	O
controlling	O
cursor	B-Application
position	O
.	O
</s>
<s>
In	O
this	O
context	O
dumb	O
terminals	O
are	O
sometimes	O
dubbed	O
glass	B-General_Concept
Teletypes	I-General_Concept
,	O
for	O
they	O
essentially	O
have	O
the	O
same	O
limited	O
functionality	O
as	O
does	O
a	O
mechanical	O
Teletype	O
.	O
</s>
<s>
This	O
type	O
of	O
dumb	O
terminal	O
is	O
still	O
supported	O
on	O
modern	O
Unix-like	B-Operating_System
systems	I-Operating_System
by	O
setting	O
the	O
environment	O
variable	O
to	O
.	O
</s>
<s>
Smart	O
or	O
intelligent	O
terminals	O
are	O
those	O
that	O
also	O
have	O
the	O
ability	O
to	O
process	O
escape	O
sequences	O
,	O
in	O
particular	O
the	O
VT52	B-Application
,	O
VT100	B-Device
or	O
ANSI	O
escape	O
sequences	O
.	O
</s>
<s>
A	O
text	O
terminal	O
,	O
or	O
often	O
just	O
terminal	O
(	O
sometimes	O
text	B-General_Concept
console	I-General_Concept
)	O
is	O
a	O
serial	O
computer	O
interface	O
for	O
text	O
entry	O
and	O
display	O
.	O
</s>
<s>
Information	O
is	O
presented	O
as	O
an	B-Application
array	I-Application
of	I-Application
pre-selected	I-Application
formed	I-Application
characters	I-Application
.	O
</s>
<s>
When	O
such	O
devices	O
use	O
a	O
video	O
display	O
such	O
as	O
a	O
cathode-ray	B-Device
tube	I-Device
,	O
they	O
are	O
called	O
a	O
"	O
video	B-Device
display	I-Device
unit	I-Device
"	O
or	O
"	O
visual	B-Device
display	I-Device
unit	I-Device
"	O
(	O
VDU	O
)	O
or	O
"	O
video	B-General_Concept
display	I-General_Concept
terminal	I-General_Concept
"	O
(	O
VDT	O
)	O
.	O
</s>
<s>
The	O
system	B-Device
console	I-Device
is	O
often	O
a	O
text	O
terminal	O
used	O
to	O
operate	O
a	O
computer	O
.	O
</s>
<s>
Modern	O
computers	O
have	O
a	O
built-in	O
keyboard	B-Device
and	O
display	O
for	O
the	O
console	O
.	O
</s>
<s>
Some	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
such	O
as	O
Linux	B-Application
and	O
FreeBSD	B-Operating_System
have	O
virtual	B-Application
consoles	I-Application
to	O
provide	O
several	O
text	O
terminals	O
on	O
a	O
single	O
computer	O
.	O
</s>
<s>
The	O
fundamental	O
type	O
of	O
application	O
running	O
on	O
a	O
text	O
terminal	O
is	O
a	O
command-line	O
interpreter	O
or	O
shell	B-Operating_System
,	O
which	O
prompts	O
for	O
commands	O
from	O
the	O
user	O
and	O
executes	O
each	O
command	O
after	O
a	O
press	O
of	O
.	O
</s>
<s>
This	O
includes	O
Unix	B-Application
shells	I-Application
and	O
some	O
interactive	B-Application
programming	I-Application
environments	O
.	O
</s>
<s>
In	O
a	O
shell	B-Operating_System
,	O
most	O
of	O
the	O
commands	O
are	O
small	O
applications	O
themselves	O
.	O
</s>
<s>
Another	O
important	O
application	O
type	O
is	O
that	O
of	O
the	O
text	B-Application
editor	I-Application
.	O
</s>
<s>
A	O
text	B-Application
editor	I-Application
typically	O
occupies	O
the	O
full	O
area	O
of	O
display	O
,	O
displays	O
one	O
or	O
more	O
text	O
documents	O
,	O
and	O
allows	O
the	O
user	O
to	O
edit	O
the	O
documents	O
.	O
</s>
<s>
The	O
text	B-Application
editor	I-Application
has	O
,	O
for	O
many	O
uses	O
,	O
been	O
replaced	O
by	O
the	O
word	B-General_Concept
processor	I-General_Concept
,	O
which	O
usually	O
provides	O
rich	O
formatting	O
features	O
that	O
the	O
text	B-Application
editor	I-Application
lacks	O
.	O
</s>
<s>
The	O
first	O
word	B-General_Concept
processors	I-General_Concept
used	O
text	O
to	O
communicate	O
the	O
structure	O
of	O
the	O
document	O
,	O
but	O
later	O
word	B-General_Concept
processors	I-General_Concept
operate	O
in	O
a	O
graphical	B-Application
environment	I-Application
and	O
provide	O
a	O
WYSIWYG	B-Application
simulation	O
of	O
the	O
formatted	O
output	O
.	O
</s>
<s>
However	O
,	O
text	B-Application
editors	I-Application
are	O
still	O
used	O
for	O
documents	O
containing	O
markup	O
such	O
as	O
DocBook	B-Protocol
or	O
LaTeX	B-Application
.	O
</s>
<s>
Programs	O
such	O
as	O
Telix	B-Protocol
and	O
Minicom	B-Language
control	O
a	O
modem	B-Application
and	O
the	O
local	O
terminal	O
to	O
let	O
the	O
user	O
interact	O
with	O
remote	O
servers	O
.	O
</s>
<s>
On	O
the	O
Internet	O
,	O
telnet	B-Protocol
and	O
ssh	B-Protocol
work	O
similarly	O
.	O
</s>
<s>
In	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
there	O
are	O
several	O
character	O
special	O
files	O
that	O
correspond	O
to	O
available	O
text	O
terminals	O
.	O
</s>
<s>
For	O
other	O
operations	O
,	O
there	O
are	O
special	O
escape	O
sequences	O
,	O
control	O
characters	O
and	O
termios	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
terminal	O
specific	O
ioctl	B-Operating_System
system	B-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
Unix	B-Application
systems	I-Application
typically	O
buffer	B-General_Concept
the	O
input	O
text	O
until	O
the	O
Enter	B-Device
key	I-Device
is	O
pressed	O
,	O
so	O
the	O
application	O
receives	O
a	O
ready	O
string	O
of	O
text	O
.	O
</s>
<s>
One	O
of	O
the	O
common	O
enhancements	O
is	O
command-line	O
editing	O
(	O
assisted	O
with	O
such	O
libraries	B-Library
as	O
readline	B-Application
)	O
;	O
it	O
also	O
may	O
give	O
access	O
to	O
command	O
history	O
.	O
</s>
<s>
This	O
mode	O
is	O
very	O
useful	O
for	O
text	B-Application
editors	I-Application
,	O
file	B-Application
managers	I-Application
and	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
To	O
achieve	O
all	O
this	O
,	O
the	O
application	O
must	O
deal	O
not	O
only	O
with	O
plain	O
text	O
strings	O
,	O
but	O
also	O
with	O
control	O
characters	O
and	O
escape	O
sequences	O
,	O
which	O
allow	O
moving	O
the	O
cursor	B-Application
to	O
an	O
arbitrary	O
position	O
,	O
clearing	O
portions	O
of	O
the	O
screen	O
,	O
changing	O
colors	O
and	O
displaying	O
special	O
characters	O
,	O
and	O
also	O
responding	O
to	O
function	B-Application
keys	I-Application
.	O
</s>
<s>
The	O
great	O
problem	O
here	O
is	O
that	O
there	O
are	O
many	O
different	O
terminals	O
and	O
terminal	B-Application
emulators	I-Application
,	O
each	O
with	O
its	O
own	O
set	O
of	O
escape	O
sequences	O
.	O
</s>
<s>
In	O
order	O
to	O
overcome	O
this	O
,	O
special	O
libraries	B-Library
(	O
such	O
as	O
curses	B-Device
)	O
have	O
been	O
created	O
,	O
together	O
with	O
terminal	O
description	O
databases	O
,	O
such	O
as	O
Termcap	B-Application
and	O
Terminfo	B-Device
.	O
</s>
<s>
A	O
block-oriented	O
terminal	O
or	O
block	O
mode	O
terminal	O
is	O
a	O
type	O
of	O
computer	B-General_Concept
terminal	I-General_Concept
that	O
communicates	O
with	O
its	O
host	B-Device
in	O
blocks	O
of	O
data	O
,	O
as	O
opposed	O
to	O
a	O
character-oriented	O
terminal	O
that	O
communicates	O
with	O
its	O
host	B-Device
one	O
character	O
at	O
a	O
time	O
.	O
</s>
<s>
A	O
block	O
oriented	O
terminal	O
may	O
be	O
card-oriented	O
,	O
display	O
oriented	O
,	O
keyboard-display	O
,	O
keyboard-printer	O
,	O
printer	O
or	O
some	O
combination	O
.	O
</s>
<s>
The	O
IBM	B-Operating_System
3270	I-Operating_System
is	O
perhaps	O
the	O
most	O
familiar	O
implementation	O
of	O
a	O
block-oriented	O
display	O
terminal	O
,	O
but	O
most	O
mainframe	B-Architecture
computer	I-Architecture
manufacturers	O
and	O
several	O
other	O
companies	O
produced	O
them	O
.	O
</s>
<s>
The	O
description	O
below	O
is	O
in	O
terms	O
of	O
the	O
3270	B-Operating_System
,	O
but	O
similar	O
considerations	O
apply	O
to	O
other	O
types	O
.	O
</s>
<s>
Block-oriented	O
terminals	O
typically	O
incorporate	O
a	O
buffer	B-General_Concept
which	O
stores	O
one	O
screen	O
or	O
more	O
of	O
data	O
,	O
and	O
also	O
stores	O
data	O
attributes	O
,	O
not	O
only	O
indicating	O
appearance	O
(	O
color	O
,	O
brightness	O
,	O
blinking	O
,	O
etc	O
.	O
)	O
</s>
<s>
In	O
a	O
typical	O
application	O
the	O
host	B-Device
sends	O
the	O
terminal	O
a	O
preformatted	O
panel	O
containing	O
both	O
static	O
data	O
and	O
fields	O
into	O
which	O
data	O
may	O
be	O
entered	O
.	O
</s>
<s>
When	O
entry	O
is	O
complete	O
(	O
or	O
ENTER	O
or	O
PF	O
key	O
pressed	O
on	O
3270s	B-Operating_System
)	O
,	O
a	O
block	O
of	O
data	O
,	O
usually	O
just	O
the	O
data	O
entered	O
by	O
the	O
operator	O
(	O
modified	O
data	O
)	O
,	O
is	O
sent	O
to	O
the	O
host	B-Device
in	O
one	O
transmission	O
.	O
</s>
<s>
The	O
3270	B-Operating_System
terminal	I-Operating_System
buffer	B-General_Concept
(	O
at	O
the	O
device	O
)	O
could	O
be	O
updated	O
on	O
a	O
single	O
character	O
basis	O
,	O
if	O
necessary	O
,	O
because	O
of	O
the	O
existence	O
of	O
a	O
"	O
set	O
buffer	B-General_Concept
address	O
order	O
"	O
(	O
SBA	O
)	O
,	O
that	O
usually	O
preceded	O
any	O
data	O
to	O
be	O
written/overwritten	O
within	O
the	O
buffer	B-General_Concept
.	O
</s>
<s>
A	O
complete	O
buffer	B-General_Concept
could	O
also	O
be	O
read	O
or	O
replaced	O
using	O
the	O
READ	O
BUFFER	B-General_Concept
command	O
or	O
WRITE	O
command	O
(	O
unformatted	O
or	O
formatted	O
in	O
the	O
case	O
of	O
the	O
3270	B-Operating_System
)	O
.	O
</s>
<s>
Block-oriented	O
terminals	O
cause	O
less	O
system	B-Operating_System
load	I-Operating_System
on	O
the	O
host	B-Device
and	O
less	O
network	O
traffic	O
than	O
character-oriented	O
terminals	O
.	O
</s>
<s>
They	O
also	O
appear	O
more	O
responsive	O
to	O
the	O
user	O
,	O
especially	O
over	O
slow	O
connections	O
,	O
since	O
editing	O
within	O
a	O
field	O
is	O
done	O
locally	O
rather	O
than	O
depending	O
on	O
echoing	B-Error_Name
from	O
the	O
host	B-Device
system	O
.	O
</s>
<s>
Early	O
terminals	O
had	O
limited	O
editing	O
capabilities	O
3270	B-Operating_System
terminals	I-Operating_System
,	O
for	O
example	O
,	O
only	O
could	O
check	O
entries	O
as	O
valid	O
numerics	O
.	O
</s>
<s>
Subsequent	O
"	O
smart	O
"	O
or	O
"	O
intelligent	O
"	O
terminals	O
incorporated	O
microprocessors	B-Architecture
and	O
supported	O
more	O
local	O
processing	O
.	O
</s>
<s>
This	O
was	O
the	O
precursor	O
of	O
the	O
HTML	B-Language
technique	O
of	O
storing	O
context	O
in	O
the	O
URL	O
as	O
data	O
to	O
be	O
passed	O
as	O
arguments	O
to	O
a	O
CGI	B-Language
program	O
.	O
</s>
<s>
Unlike	O
a	O
character-oriented	O
terminal	O
,	O
where	O
typing	O
a	O
character	O
into	O
the	O
last	O
position	O
of	O
the	O
screen	O
usually	O
causes	O
the	O
terminal	O
to	O
scroll	O
down	O
one	O
line	O
,	O
entering	O
data	O
into	O
the	O
last	O
screen	O
position	O
on	O
a	O
block-oriented	O
terminal	O
usually	O
causes	O
the	O
cursor	B-Application
to	O
wrap	O
—	O
move	O
to	O
the	O
start	O
of	O
the	O
first	O
enterable	O
field	O
.	O
</s>
<s>
Likewise	O
a	O
protected	O
field	O
following	O
an	O
enterable	O
field	O
might	O
lock	O
the	O
keyboard	B-Device
and	O
sound	O
an	O
audible	O
alarm	O
if	O
the	O
operator	O
attempted	O
to	O
enter	O
more	O
data	O
into	O
the	O
field	O
than	O
allowed	O
.	O
</s>
<s>
Graphical	O
terminals	O
are	O
divided	O
into	O
vector-mode	O
terminals	O
,	O
and	O
raster	B-Algorithm
mode	I-Algorithm
.	O
</s>
<s>
A	O
vector-mode	O
display	O
directly	O
draws	O
lines	O
on	O
the	O
face	O
of	O
a	O
cathode-ray	B-Device
tube	I-Device
under	O
control	O
of	O
the	O
host	B-Device
computer	I-Device
system	O
.	O
</s>
<s>
Practically	O
all	O
modern	O
graphic	O
displays	O
are	O
raster-mode	O
,	O
descended	O
from	O
the	O
picture	O
scanning	O
techniques	O
used	O
for	O
television	O
,	O
in	O
which	O
the	O
visual	O
elements	O
are	O
a	O
rectangular	O
array	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
Since	O
the	O
raster	B-Algorithm
image	I-Algorithm
is	O
only	O
perceptible	O
to	O
the	O
human	O
eye	O
as	O
a	O
whole	O
for	O
a	O
very	O
short	O
time	O
,	O
the	O
raster	O
must	O
be	O
refreshed	O
many	O
times	O
per	O
second	O
to	O
give	O
the	O
appearance	O
of	O
a	O
persistent	O
display	O
.	O
</s>
<s>
The	O
modern	O
term	O
for	O
graphical	O
terminal	O
is	O
"	O
thin	B-Device
client	I-Device
"	O
.	O
</s>
<s>
A	O
thin	B-Device
client	I-Device
typically	O
uses	O
a	O
protocol	O
like	O
X11	B-Operating_System
for	O
Unix	B-Application
terminals	O
,	O
or	O
RDP	B-Protocol
for	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
an	O
industry	O
consortium	O
attempted	O
to	O
define	O
a	O
standard	O
,	O
AlphaWindows	B-Application
,	O
that	O
would	O
allow	O
a	O
single	O
CRT	B-Device
screen	I-Device
to	O
implement	O
multiple	O
windows	O
,	O
each	O
of	O
which	O
was	O
to	O
behave	O
as	O
a	O
distinct	O
terminal	O
.	O
</s>
<s>
Unfortunately	O
,	O
like	O
I2O	B-General_Concept
,	O
this	O
suffered	O
from	O
being	O
run	O
as	O
a	O
closed	O
standard	O
:	O
non-members	O
were	O
unable	O
to	O
obtain	O
even	O
minimal	O
information	O
and	O
there	O
was	O
no	O
realistic	O
way	O
a	O
small	O
company	O
or	O
independent	O
developer	O
could	O
join	O
the	O
consortium	O
.	O
</s>
<s>
An	O
"	O
intelligent	O
"	O
terminal	O
does	O
its	O
own	O
processing	O
,	O
usually	O
implying	O
a	O
microprocessor	B-Architecture
is	O
built	O
in	O
,	O
but	O
not	O
all	O
terminals	O
with	O
microprocessors	B-Architecture
did	O
any	O
real	O
processing	O
of	O
input	O
:	O
the	O
main	O
computer	O
to	O
which	O
it	O
was	O
attached	O
would	O
have	O
to	O
respond	O
quickly	O
to	O
each	O
keystroke	O
.	O
</s>
<s>
Notable	O
examples	O
include	O
the	O
IBM	B-Device
2250	I-Device
,	O
predecessor	O
to	O
the	O
IBM	O
3250	O
and	O
IBM	O
5080	O
,	O
and	O
IBM	B-Device
2260	I-Device
,	O
predecessor	O
to	O
the	O
IBM	B-Operating_System
3270	I-Operating_System
,	O
introduced	O
with	O
System/360	B-Application
in	O
1964	O
.	O
</s>
<s>
Most	O
terminals	O
were	O
connected	O
to	O
minicomputers	B-Architecture
or	O
mainframe	B-Architecture
computers	I-Architecture
and	O
often	O
had	O
a	O
green	O
or	O
amber	B-Device
screen	I-Device
.	O
</s>
<s>
Typically	O
terminals	O
communicate	O
with	O
the	O
computer	O
via	O
a	O
serial	B-Protocol
port	I-Protocol
via	O
a	O
null	O
modem	B-Application
cable	O
,	O
often	O
using	O
an	O
EIA	O
RS-232	O
or	O
RS-422	O
or	O
RS-423	O
or	O
a	O
current	O
loop	O
serial	B-Protocol
interface	I-Protocol
.	O
</s>
<s>
IBM	O
systems	O
typically	O
communicated	O
over	O
a	O
Bus	B-Device
and	I-Device
Tag	I-Device
channel	I-Device
,	O
a	O
coaxial	O
cable	O
using	O
a	O
proprietary	O
protocol	O
,	O
a	O
communications	O
link	O
using	O
Binary	B-Protocol
Synchronous	I-Protocol
Communications	I-Protocol
or	O
IBM	O
's	O
SNA	B-Architecture
protocol	O
,	O
but	O
for	O
many	O
DEC	O
,	O
Data	O
General	O
and	O
NCR	O
(	O
and	O
so	O
on	O
)	O
computers	O
there	O
were	O
many	O
visual	O
display	O
suppliers	O
competing	O
against	O
the	O
computer	O
manufacturer	O
for	O
terminals	O
to	O
expand	O
the	O
systems	O
.	O
</s>
<s>
In	O
fact	O
,	O
the	O
instruction	O
design	O
for	O
the	O
Intel	B-General_Concept
8008	I-General_Concept
was	O
originally	O
conceived	O
at	O
Computer	B-General_Concept
Terminal	I-General_Concept
Corporation	O
as	O
the	O
processor	O
for	O
the	O
Datapoint	B-Device
2200	I-Device
.	O
</s>
<s>
From	O
the	O
introduction	O
of	O
the	O
IBM	B-Operating_System
3270	I-Operating_System
,	O
and	O
the	O
DEC	B-Device
VT100	I-Device
(	O
1978	O
)	O
,	O
the	O
user	O
and	O
programmer	O
could	O
notice	O
significant	O
advantages	O
in	O
VDU	O
technology	O
improvements	O
,	O
yet	O
not	O
all	O
programmers	O
used	O
the	O
features	O
of	O
the	O
new	O
terminals	O
(	O
backward	B-General_Concept
compatibility	I-General_Concept
in	O
the	O
VT100	B-Device
and	O
later	O
TeleVideo	O
terminals	O
,	O
for	O
example	O
,	O
with	O
"	O
dumb	O
terminals	O
"	O
allowed	O
programmers	O
to	O
continue	O
to	O
use	O
older	O
software	B-Application
)	O
.	O
</s>
<s>
Some	O
dumb	O
terminals	O
had	O
been	O
able	O
to	O
respond	O
to	O
a	O
few	O
escape	O
sequences	O
without	O
needing	O
microprocessors	B-Architecture
:	O
they	O
used	O
multiple	O
printed	O
circuit	O
boards	O
with	O
many	O
integrated	O
circuits	O
;	O
the	O
single	O
factor	O
that	O
classed	O
a	O
terminal	O
as	O
"	O
intelligent	O
"	O
was	O
its	O
ability	O
to	O
process	O
user-input	O
within	O
the	O
terminal	O
—	O
not	O
interrupting	O
the	O
main	O
computer	O
at	O
each	O
keystroke	O
—	O
and	O
send	O
a	O
block	O
of	O
data	O
at	O
a	O
time	O
(	O
for	O
example	O
:	O
when	O
the	O
user	O
has	O
finished	O
a	O
whole	O
field	O
or	O
form	O
)	O
.	O
</s>
<s>
Most	O
terminals	O
in	O
the	O
early	O
1980s	O
,	O
such	O
as	O
ADM-3A	B-Device
,	O
TVI912	O
,	O
Data	O
General	O
D2	O
,	O
DEC	O
VT52	B-Application
,	O
despite	O
the	O
introduction	O
of	O
ANSI	O
terminals	O
in	O
1978	O
,	O
were	O
essentially	O
"	O
dumb	O
"	O
terminals	O
,	O
although	O
some	O
of	O
them	O
(	O
such	O
as	O
the	O
later	O
ADM	O
and	O
TVI	O
models	O
)	O
did	O
have	O
a	O
primitive	O
block-send	O
capability	O
.	O
</s>
<s>
Common	O
early	O
uses	O
of	O
local	O
processing	O
power	O
included	O
features	O
that	O
had	O
little	O
to	O
do	O
with	O
off-loading	O
data	O
processing	O
from	O
the	O
host	B-Device
computer	I-Device
but	O
added	O
useful	O
features	O
such	O
as	O
printing	O
to	O
a	O
local	O
printer	O
,	O
buffered	O
serial	O
data	O
transmission	O
and	O
serial	O
handshaking	O
(	O
to	O
accommodate	O
higher	O
serial	O
transfer	O
speeds	O
)	O
,	O
and	O
more	O
sophisticated	O
character	O
attributes	O
for	O
the	O
display	O
,	O
as	O
well	O
as	O
the	O
ability	O
to	O
switch	O
emulation	O
modes	O
to	O
mimic	O
competitor	O
's	O
models	O
,	O
that	O
became	O
increasingly	O
important	O
selling	O
features	O
during	O
the	O
1980s	O
especially	O
,	O
when	O
buyers	O
could	O
mix	O
and	O
match	O
different	O
suppliers	O
 '	O
equipment	O
to	O
a	O
greater	O
extent	O
than	O
before	O
.	O
</s>
<s>
The	O
advance	O
in	O
microprocessors	B-Architecture
and	O
lower	O
memory	O
costs	O
made	O
it	O
possible	O
for	O
the	O
terminal	O
to	O
handle	O
editing	O
operations	O
such	O
as	O
inserting	O
characters	O
within	O
a	O
field	O
that	O
may	O
have	O
previously	O
required	O
a	O
full	O
screen-full	O
of	O
characters	O
to	O
be	O
re-sent	O
from	O
the	O
computer	O
,	O
possibly	O
over	O
a	O
slow	O
modem	B-Application
line	O
.	O
</s>
<s>
Providing	O
even	O
more	O
processing	O
possibilities	O
,	O
workstations	O
like	O
the	O
TeleVideo	O
TS-800	O
could	O
run	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
blurring	O
the	O
distinction	O
between	O
terminal	O
and	O
Personal	B-Device
Computer	I-Device
.	O
</s>
<s>
Another	O
of	O
the	O
motivations	O
for	O
development	O
of	O
the	O
microprocessor	B-Architecture
was	O
to	O
simplify	O
and	O
reduce	O
the	O
electronics	O
required	O
in	O
a	O
terminal	O
.	O
</s>
<s>
That	O
also	O
made	O
it	O
practicable	O
to	O
load	O
several	O
"	O
personalities	O
"	O
into	O
a	O
single	O
terminal	O
,	O
so	O
a	O
Qume	O
QVT-102	O
could	O
emulate	O
many	O
popular	O
terminals	O
of	O
the	O
day	O
,	O
and	O
so	O
be	O
sold	O
into	O
organizations	O
that	O
did	O
not	O
wish	O
to	O
make	O
any	O
software	B-Application
changes	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
VT100	B-Device
,	O
Heathkit	O
H19	O
in	O
ANSI	O
mode	O
,	O
Televideo	O
970	O
,	O
Data	O
General	O
D460	O
,	O
and	O
Qume	O
QVT-108	O
terminals	O
all	O
followed	O
the	O
ANSI	O
standard	O
,	O
yet	O
differences	O
might	O
exist	O
in	O
codes	O
from	O
function	B-Application
keys	I-Application
,	O
what	O
character	O
attributes	O
were	O
available	O
,	O
block-sending	O
of	O
fields	O
within	O
forms	O
,	O
"	O
foreign	O
"	O
character	O
facilities	O
,	O
and	O
handling	O
of	O
printers	O
connected	O
to	O
the	O
back	O
of	O
the	O
screen	O
.	O
</s>
<s>
While	O
early	O
IBM	B-Device
PCs	I-Device
had	O
single-color	O
green	B-Device
screens	I-Device
,	O
these	O
screens	O
were	O
not	O
terminals	O
.	O
</s>
<s>
The	O
screen	O
of	O
a	O
PC	O
did	O
not	O
contain	O
any	O
character	O
generation	O
hardware	B-Architecture
;	O
all	O
video	O
signals	O
and	O
video	O
formatting	O
were	O
generated	O
by	O
the	O
video	O
display	O
card	O
in	O
the	O
PC	O
,	O
or	O
(	O
in	O
most	O
graphics	O
modes	O
)	O
by	O
the	O
CPU	B-General_Concept
and	O
software	B-Application
.	O
</s>
<s>
An	O
IBM	B-Device
PC	I-Device
monitor	B-Device
,	O
whether	O
it	O
was	O
the	O
green	B-Device
monochrome	I-Device
display	I-Device
or	O
the	O
16-color	O
display	O
,	O
was	O
technically	O
much	O
more	O
similar	O
to	O
an	O
analog	O
TV	O
set	O
(	O
without	O
a	O
tuner	O
)	O
than	O
to	O
a	O
terminal	O
.	O
</s>
<s>
With	O
suitable	O
software	B-Application
a	O
PC	O
could	O
,	O
however	O
,	O
emulate	O
a	O
terminal	O
,	O
and	O
in	O
that	O
capacity	O
it	O
could	O
be	O
connected	O
to	O
a	O
mainframe	B-Architecture
or	O
minicomputer	B-Architecture
.	O
</s>
<s>
The	O
Data	B-Device
General/One	I-Device
could	O
be	O
booted	O
into	O
terminal	B-Application
emulator	I-Application
mode	O
from	O
its	O
ROM	O
.	O
</s>
<s>
Eventually	O
microprocessor-based	O
personal	B-Device
computers	I-Device
greatly	O
reduced	O
the	O
market	O
demand	O
for	O
conventional	O
terminals	O
.	O
</s>
<s>
In	O
the	O
1990s	O
especially	O
,	O
"	O
thin	B-Device
clients	I-Device
"	O
and	O
X	B-Protocol
terminals	I-Protocol
have	O
combined	O
economical	O
local	O
processing	O
power	O
with	O
central	O
,	O
shared	O
computer	O
facilities	O
to	O
retain	O
some	O
of	O
the	O
advantages	O
of	O
terminals	O
over	O
personal	B-Device
computers	I-Device
:	O
</s>
<s>
Today	O
,	O
most	O
PC	O
telnet	B-Protocol
clients	O
provide	O
emulation	O
of	O
the	O
most	O
common	O
terminal	O
,	O
the	O
DEC	B-Device
VT100	I-Device
,	O
using	O
the	O
ANSI	O
escape	O
code	O
standard	O
X3.64	O
,	O
or	O
could	O
run	O
as	O
X	B-Protocol
terminals	I-Protocol
using	O
software	B-Application
such	O
as	O
Cygwin/X	B-Application
under	O
Microsoft	B-Application
Windows	I-Application
or	O
X.Org	B-Operating_System
Server	I-Operating_System
software	B-Application
under	O
Linux	B-Application
.	O
</s>
<s>
Since	O
the	O
advent	O
and	O
subsequent	O
popularization	O
of	O
the	O
personal	B-Device
computer	I-Device
,	O
few	O
genuine	O
hardware	B-Architecture
terminals	O
are	O
used	O
to	O
interface	O
with	O
computers	O
today	O
.	O
</s>
<s>
Using	O
the	O
monitor	B-Device
and	O
keyboard	B-Device
,	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
like	O
Linux	B-Application
and	O
the	O
BSD	B-Operating_System
derivatives	O
feature	O
virtual	B-Application
consoles	I-Application
,	O
which	O
are	O
mostly	O
independent	O
from	O
the	O
hardware	B-Architecture
used	O
.	O
</s>
<s>
When	O
using	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
or	O
GUI	B-Application
)	O
like	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
one	O
's	O
display	O
is	O
typically	O
occupied	O
by	O
a	O
collection	O
of	O
windows	O
associated	O
with	O
various	O
applications	O
,	O
rather	O
than	O
a	O
single	O
stream	O
of	O
text	O
associated	O
with	O
a	O
single	O
process	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
one	O
may	O
use	O
a	O
terminal	B-Application
emulator	I-Application
application	O
within	O
the	O
windowing	O
environment	O
.	O
</s>
<s>
This	O
arrangement	O
permits	O
terminal-like	O
interaction	O
with	O
the	O
computer	O
(	O
for	O
running	O
a	O
command-line	O
interpreter	O
,	O
for	O
example	O
)	O
without	O
the	O
need	O
for	O
a	O
physical	B-General_Concept
terminal	I-General_Concept
device	O
;	O
it	O
can	O
even	O
run	O
multiple	O
terminal	B-Application
emulators	I-Application
on	O
the	O
same	O
device	O
.	O
</s>
<s>
A	O
terminal	B-Application
emulator	I-Application
is	O
a	O
piece	O
of	O
software	B-Application
that	O
emulates	O
a	O
text	O
terminal	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
before	O
the	O
widespread	O
use	O
of	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
and	O
broadband	O
internet	O
access	O
,	O
many	O
computers	O
would	O
use	O
a	O
serial	O
access	O
program	O
to	O
communicate	O
with	O
other	O
computers	O
via	O
telephone	O
line	O
or	O
serial	O
device	O
.	O
</s>
<s>
When	O
the	O
first	O
Macintosh	B-Device
was	O
released	O
,	O
a	O
program	O
called	O
MacTerminal	B-Operating_System
was	O
used	O
to	O
communicate	O
with	O
many	O
computers	O
,	O
including	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
Dec	O
Terminal	O
was	O
one	O
of	O
the	O
first	O
terminal	B-Application
programs	I-Application
for	O
the	O
popular	O
Altair	B-Architecture
.	O
</s>
<s>
The	O
Win32	B-Application
console	I-Application
on	O
Windows	O
does	O
not	O
emulate	O
a	O
physical	B-General_Concept
terminal	I-General_Concept
that	O
supports	O
escape	O
sequences	O
so	O
SSH	B-Protocol
and	O
Telnet	B-Protocol
programs	O
(	O
for	O
logging	O
in	O
textually	O
to	O
remote	O
computers	O
)	O
for	O
Windows	O
,	O
including	O
the	O
Telnet	B-Protocol
program	O
bundled	O
with	O
some	O
versions	O
of	O
Windows	O
,	O
often	O
incorporate	O
their	O
own	O
code	O
to	O
process	O
escape	O
sequences	O
.	O
</s>
<s>
The	O
terminal	B-Application
emulators	I-Application
on	O
most	O
Unix-like	B-Operating_System
systems	I-Operating_System
—	O
such	O
as	O
,	O
for	O
example	O
,	O
gnome-terminal	B-Language
,	O
qterminal	O
,	O
xterm	B-Language
,	O
and	O
Terminal.app	B-Application
—	O
do	O
emulate	O
physical	B-General_Concept
terminals	I-General_Concept
including	O
support	O
for	O
escape	O
sequences	O
;	O
e.g.	O
,	O
xterm	B-Language
can	O
emulate	O
the	O
VT220	B-Device
and	O
Tektronix	B-General_Concept
4010	I-General_Concept
hardware	B-Architecture
terminals	O
.	O
</s>
<s>
Terminals	O
can	O
operate	O
in	O
various	O
modes	O
,	O
relating	O
to	O
when	O
they	O
send	O
input	O
typed	O
by	O
the	O
user	O
on	O
the	O
keyboard	B-Device
to	O
the	O
receiving	O
system	O
(	O
whatever	O
that	O
may	O
be	O
)	O
:	O
</s>
<s>
The	O
user	O
can	O
enter	O
input	O
into	O
multiple	O
fields	O
in	O
a	O
form	O
on	O
the	O
screen	O
(	O
defined	O
to	O
the	O
terminal	O
by	O
the	O
receiving	O
system	O
)	O
,	O
moving	O
the	O
cursor	B-Application
around	O
the	O
screen	O
using	O
keys	O
such	O
as	O
and	O
the	O
arrow	B-Device
keys	I-Device
and	O
performing	O
editing	O
functions	B-Operating_System
locally	O
using	O
,	O
,	O
and	O
so	O
forth	O
.	O
</s>
<s>
Whilst	O
the	O
key	O
will	O
cause	O
an	O
input	O
line	O
to	O
be	O
sent	O
to	O
the	O
host	B-Device
in	O
line-at-a-time	O
mode	O
,	O
the	O
key	O
will	O
rather	O
cause	O
the	O
terminal	O
to	O
transmit	O
the	O
contents	O
of	O
the	O
character	O
row	O
where	O
the	O
cursor	B-Application
is	O
currently	O
positioned	O
to	O
the	O
host	B-Device
,	O
host-issued	O
prompts	O
and	O
all	O
.	O
</s>
<s>
Some	O
block-mode	O
terminals	O
have	O
both	O
an	O
and	O
local	O
cursor	B-Application
moving	O
keys	O
such	O
as	O
and	O
.	O
</s>
<s>
Different	O
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
require	O
different	O
degrees	O
of	O
mode	O
support	O
when	O
terminals	O
are	O
used	O
as	O
computer	B-General_Concept
terminals	I-General_Concept
.	O
</s>
<s>
The	O
POSIX	B-Application
terminal	I-Application
interface	I-Application
,	O
as	O
provided	O
by	O
Unix	B-Application
and	O
POSIX-compliant	O
operating	B-General_Concept
systems	I-General_Concept
,	O
does	O
not	O
accommodate	O
block-mode	O
terminals	O
at	O
all	O
,	O
and	O
only	O
rarely	O
requires	O
the	O
terminal	O
itself	O
to	O
be	O
in	O
line-at-a-time	O
mode	O
,	O
since	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
required	O
to	O
provide	O
canonical	O
input	O
mode	O
,	O
where	O
the	O
terminal	O
device	O
driver	O
in	O
the	O
operating	B-General_Concept
system	I-General_Concept
emulates	O
local	B-Error_Name
echo	I-Error_Name
in	O
the	O
terminal	O
,	O
and	O
performs	O
line	O
editing	O
functions	B-Operating_System
at	O
the	O
host	B-Device
end	O
.	O
</s>
<s>
Most	O
usually	O
,	O
and	O
especially	O
so	O
that	O
the	O
host	B-Device
system	O
can	O
support	O
non-canonical	O
input	O
mode	O
,	O
terminals	O
for	O
POSIX-compliant	O
systems	O
are	O
always	O
in	O
character-at-a-time	O
mode	O
.	O
</s>
<s>
In	O
contrast	O
,	O
IBM	B-Operating_System
3270	I-Operating_System
terminals	O
connected	O
to	O
MVS	B-Application
systems	O
are	O
always	O
required	O
to	O
be	O
in	O
block	O
mode	O
.	O
</s>
