<s>
The	O
VT420	B-Application
is	O
an	O
ANSI	O
standard	O
computer	B-General_Concept
terminal	I-General_Concept
introduced	O
in	O
1990	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
.	O
</s>
<s>
The	O
420	O
is	O
the	O
only	O
model	O
in	O
the	O
400	O
series	O
,	O
replacing	O
the	O
VT320	B-Application
.	O
</s>
<s>
There	O
are	O
no	O
color	O
or	O
graphics-capable	O
400	O
series	O
terminals	O
;	O
the	O
VT340	B-Application
remained	O
in	O
production	O
for	O
those	O
requiring	O
ReGIS	B-Application
and	O
Sixel	O
graphics	O
and	O
color	O
support	O
.	O
</s>
<s>
The	O
entire	O
lineup	O
of	O
VT300s	O
and	O
VT420	B-Application
was	O
eventually	O
replaced	O
by	O
the	O
relatively	O
unknown	O
VT500	B-Application
series	I-Application
starting	O
in	O
1993	O
.	O
</s>
<s>
The	O
VT420	B-Application
is	O
essentially	O
an	O
updated	O
VT320	B-Application
,	O
adding	O
the	O
multi-session	O
capabilities	O
originally	O
introduced	O
on	O
the	O
VT330	B-Application
and	O
VT340	B-Application
.	O
</s>
<s>
Those	O
two	O
models	O
include	O
a	O
system	O
known	O
as	O
TD/SMP	O
which	O
allows	O
two	O
sessions	O
to	O
be	O
multiplexed	O
over	O
a	O
single	O
serial	O
connection	O
to	O
a	O
compatible	O
terminal	B-Device
server	I-Device
.	O
</s>
<s>
Alternately	O
,	O
the	O
two	O
sessions	O
can	O
be	O
supported	O
by	O
separate	O
serial	O
connections	O
on	O
those	O
models	O
with	O
multiple	O
MMJ	B-Device
ports	O
.	O
</s>
<s>
Using	O
either	O
method	O
,	O
the	O
VT330/340/420	O
can	O
either	O
show	O
the	O
two	O
sessions	O
behind	O
each	O
other	O
,	O
using	O
a	O
key	O
sequence	O
to	O
flip	O
back	O
and	O
forth	O
,	O
or	O
split	O
the	O
screen	O
horizontally	O
to	O
display	O
the	O
sessions	O
one	O
above	O
the	O
other	O
,	O
or	O
vertically	O
side-by-side	O
.	O
</s>
<s>
The	O
VT420	B-Application
also	O
added	O
a	O
number	O
of	O
more	O
minor	O
features	O
.	O
</s>
<s>
The	O
VT420	B-Application
has	O
a	O
total	O
of	O
5	O
sets	O
of	O
94	O
characters	O
for	O
normal	O
VT	O
operation	O
,	O
another	O
3	O
sets	O
of	O
128	O
PC	O
characters	O
,	O
and	O
1	O
set	O
of	O
96	O
characters	O
containing	O
various	O
graphics	O
and	O
math	O
symbols	O
.	O
</s>
<s>
Like	O
all	O
models	O
since	O
the	O
VT200	B-Device
series	I-Device
,	O
the	O
user	O
can	O
also	O
upload	O
a	O
custom	O
character	O
set	O
of	O
their	O
own	O
design	O
using	O
the	O
Sixel	O
system	O
.	O
</s>
<s>
All	O
DEC	O
terminals	O
that	O
came	O
after	O
the	O
VT100	B-Device
,	O
including	O
the	O
VT420	B-Application
,	O
are	O
able	O
to	O
emulate	O
their	O
ancestors	O
.	O
</s>
<s>
The	O
VT420	B-Application
has	O
VT100	B-Device
and	O
VT52	B-Application
emulating	O
modes	O
.	O
</s>
<s>
The	O
screen	O
itself	O
is	O
a	O
14	O
"	O
flat	O
CRT	B-Device
with	O
a	O
resolution	O
of	O
800	O
(	O
horizontal	O
)	O
by	O
400	O
(	O
vertical	O
)	O
pixels	O
.	O
</s>
<s>
The	O
MMJ	B-Device
ports	O
can	O
operate	O
at	O
speeds	O
up	O
to	O
38,400	O
bit/s	O
,	O
double	O
that	O
of	O
the	O
VT300s	O
 '	O
maximum	O
19,200	O
bit/s	O
.	O
</s>
