<s>
The	O
VT520	B-Application
is	O
an	O
ANSI	O
standard	O
computer	B-General_Concept
terminal	I-General_Concept
introduced	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
in	O
1993	O
and	O
1994	O
.	O
</s>
<s>
The	O
VT520	B-Application
is	O
a	O
multi-session	O
monochrome	O
text-only	O
terminal	O
with	O
a	O
built-in	O
14	O
"	O
monitor	O
.	O
</s>
<s>
The	O
VT510	B-Application
was	O
a	O
single-session	O
version	O
,	O
while	O
the	O
VT525	B-Application
added	O
color	O
support	O
and	O
used	O
a	O
separate	O
external	O
monitor	O
.	O
</s>
<s>
The	O
VT500s	B-Application
replaced	O
all	O
existing	O
models	O
of	O
DEC	O
's	O
VT	O
line	O
,	O
which	O
at	O
that	O
time	O
consisted	O
of	O
just	O
the	O
VT420	B-Application
text	O
and	O
VT340	B-Application
graphics	O
terminals	O
.	O
</s>
<s>
It	O
was	O
introduced	O
in	O
an	O
era	O
when	O
the	O
market	O
was	O
being	O
flooded	O
by	O
low-cost	O
IBM	B-Device
PC	I-Device
clones	O
which	O
could	O
perform	O
the	O
same	O
functions	O
using	O
a	O
terminal	B-Application
emulator	I-Application
while	O
also	O
running	O
other	O
software	O
.	O
</s>
<s>
DEC	O
introduced	O
the	O
VT500s	B-Application
only	O
a	O
short	O
time	O
before	O
selling	O
off	O
their	O
entire	O
terminal	O
division	O
in	O
August	O
1995	O
.	O
</s>
<s>
The	O
VT520	B-Application
was	O
available	O
from	O
Boundless	O
Technologies	O
until	O
the	O
company	O
went	O
defunct	O
in	O
2003	O
.	O
</s>
<s>
When	O
equipped	O
with	O
a	O
terminal	B-Application
emulator	I-Application
,	O
these	O
machines	O
could	O
perform	O
all	O
the	O
functions	O
of	O
a	O
DEC	O
terminal	O
,	O
as	O
well	O
as	O
running	O
software	O
locally	O
.	O
</s>
<s>
The	O
terminal	O
market	O
began	O
to	O
crash	O
,	O
but	O
remained	O
important	O
to	O
DEC	O
's	O
core	O
minicomputer	B-Architecture
business	O
.	O
</s>
<s>
DEC	O
responded	O
by	O
introducing	O
the	O
VT500	B-Application
series	O
as	O
simplified	O
and	O
lower-cost	O
options	O
to	O
the	O
existing	O
VT420	B-Application
and	O
VT340	B-Application
.	O
</s>
<s>
The	O
new	O
500s	O
were	O
text-only	O
but	O
they	O
added	O
an	O
RS-232C	O
serial	O
port	O
and	O
a	O
Centronics	B-Device
port	I-Device
as	O
well	O
as	O
a	O
PS/2	B-Device
keyboard	O
connector	O
which	O
made	O
them	O
easier	O
to	O
integrate	O
into	O
a	O
mixed	O
computing	O
environment	O
.	O
</s>
<s>
They	O
also	O
had	O
two	O
DEC	O
proprietary	O
MMJ	B-Device
serial	O
connectors	O
and	O
a	O
DEC	O
proprietary	O
keyboard	O
port	O
like	O
their	O
predecessors	O
.	O
</s>
<s>
The	O
VT510	B-Application
was	O
introduced	O
in	O
1993	O
as	O
an	O
all-in-one	O
unit	O
with	O
a	O
built-in	O
14	O
"	O
display	O
.	O
</s>
<s>
The	O
VT520	B-Application
was	O
similar	O
but	O
supported	O
up	O
to	O
4	O
sessions	O
using	O
a	O
system	O
known	O
as	O
TD/SMP	O
.	O
</s>
<s>
The	O
later	O
VT525	B-Application
color	O
terminal	O
dispensed	O
with	O
the	O
integrated	O
monitor	O
as	O
well	O
,	O
packaging	O
the	O
system	O
into	O
a	O
pizza	B-General_Concept
box	I-General_Concept
case	I-General_Concept
with	O
an	O
SVGA	O
port	O
for	O
connection	O
to	O
an	O
external	O
user-supplied	O
monitor	O
.	O
</s>
<s>
Like	O
all	O
models	O
of	O
the	O
VT	O
series	O
,	O
the	O
VT500	B-Application
's	O
primary	O
purpose	O
is	O
to	O
act	O
as	O
an	O
ANSI	O
standard	O
terminal	O
.	O
</s>
<s>
The	O
VT510	B-Application
supported	O
only	O
a	O
single	O
session	O
,	O
while	O
the	O
520	O
and	O
525	O
supported	O
up	O
to	O
four	O
sessions	O
,	O
up	O
from	O
two	O
in	O
earlier	O
VTs	O
.	O
</s>
<s>
All	O
models	O
have	O
multiple	O
character	B-General_Concept
sets	I-General_Concept
in	O
ROM	B-Device
,	O
supporting	O
DEC	O
,	O
international	O
and	O
PC	O
characters	O
.	O
</s>
<s>
They	O
can	O
also	O
replace	O
any	O
of	O
these	O
by	O
downloading	O
custom	O
characters	O
using	O
sixels	O
,	O
and	O
perform	O
single-character	O
swaps	O
using	O
the	O
National	O
Replacement	O
Character	B-General_Concept
Set	I-General_Concept
,	O
swapping	O
with	O
for	O
use	O
with	O
UK	O
keyboards	O
for	O
instance	O
.	O
</s>
<s>
Like	O
earlier	O
models	O
of	O
the	O
VT	O
line	O
,	O
the	O
500s	O
could	O
be	O
put	O
into	O
modes	O
emulating	O
the	O
VT100	B-Device
and	O
VT52	B-Application
,	O
but	O
added	O
a	O
wide	O
variety	O
of	O
other	O
emulations	O
for	O
Wyse	O
,	O
ADDS	O
TeleVideo	O
and	O
other	O
terminals	O
.	O
</s>
<s>
Another	O
new	O
feature	O
was	O
the	O
inclusion	O
of	O
a	O
set	O
of	O
desk	B-Application
accessories	I-Application
running	O
on	O
the	O
terminal	O
's	O
CPU	O
.	O
</s>
<s>
These	O
included	O
a	O
calculator	O
,	O
alarm	O
clock	O
,	O
calendar	O
,	O
and	O
a	O
character	B-General_Concept
set	I-General_Concept
viewer	O
.	O
</s>
<s>
Terminal	B-Application
emulator	I-Application
specifications	O
may	O
refer	O
to	O
VT500	B-Application
instead	O
of	O
VT510	B-Application
,	O
VT520	B-Application
and	O
VT525	B-Application
in	O
the	O
statements	O
about	O
their	O
compatibility	O
.	O
</s>
