<s>
talk	O
is	O
a	O
Unix	B-Application
text	B-Protocol
chat	I-Protocol
program	O
,	O
originally	O
allowing	O
messaging	O
only	O
between	O
the	O
users	O
logged	O
on	O
to	O
one	O
multi-user	O
computerbut	O
later	O
extended	O
to	O
allow	O
chat	B-Protocol
to	O
users	O
on	O
other	O
systems	O
.	O
</s>
<s>
Although	O
largely	O
superseded	O
by	O
IRC	B-Protocol
and	O
other	O
modern	O
systems	O
,	O
it	O
is	O
still	O
included	O
with	O
most	O
Unix-like	B-Operating_System
systems	I-Operating_System
today	O
,	O
including	O
Linux	B-Application
,	O
BSD	B-Operating_System
systems	O
and	O
macOS	B-Application
.	O
</s>
<s>
Similar	O
facilities	O
existed	O
on	O
earlier	O
system	O
such	O
as	O
Multics	B-Application
,	O
CTSS	B-Operating_System
,	O
PLATO	B-Operating_System
,	O
and	O
NLS	O
.	O
</s>
<s>
More	O
modern	O
versions	O
use	O
curses	B-Device
to	O
break	O
the	O
terminal	O
into	O
multiple	O
zones	O
for	O
each	O
user	O
,	O
thus	O
avoiding	O
intermingling	O
text	O
.	O
</s>
<s>
In	O
1983	O
,	O
a	O
new	O
version	O
of	O
talk	O
was	O
introduced	O
as	O
a	O
Unix	B-Application
command	I-Application
with	O
4.2BSD	O
,	O
and	O
would	O
also	O
accommodate	O
electronic	O
conversations	O
between	O
users	O
on	O
different	O
machines	O
.	O
</s>
<s>
Follow-ons	O
to	O
talk	O
included	O
ntalk	B-Device
,	O
Britt	O
Yenne	O
's	O
ytalk	B-Device
and	O
Roger	O
Espel	O
Llima	O
's	O
utalk	O
.	O
</s>
<s>
ytalk	B-Device
was	O
the	O
first	O
of	O
these	O
to	O
allow	O
conversations	O
between	O
more	O
than	O
two	O
users	O
,	O
and	O
was	O
written	O
in	O
part	O
to	O
allow	O
communication	O
between	O
users	O
on	O
computers	O
with	O
different	O
endianness	O
.	O
</s>
<s>
utalk	O
uses	O
a	O
special	O
protocol	O
over	O
UDP	B-Protocol
(	O
instead	O
of	O
TCP	B-Protocol
used	O
by	O
the	O
rest	O
)	O
that	O
is	O
more	O
efficient	O
and	O
allows	O
edition	O
of	O
the	O
entire	O
screen	O
.	O
</s>
<s>
This	O
leads	O
to	O
a	O
more	O
immediate	O
feel	O
to	O
the	O
discussion	O
than	O
recent	O
instant	B-Application
messaging	I-Application
clients	O
or	O
IRC	B-Protocol
.	O
</s>
<s>
A	O
similar	O
program	O
exists	O
on	O
VMS	B-Operating_System
systems	O
called	O
phone	O
.	O
</s>
