<s>
In	O
computer	O
terminology	O
,	O
a	O
fill	B-General_Concept
character	I-General_Concept
is	O
a	O
character	O
transmitted	O
solely	O
for	O
the	O
purpose	O
of	O
consuming	O
time	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
fill	B-General_Concept
characters	I-General_Concept
provide	O
a	O
simple	O
way	O
of	O
timing	O
required	O
idle	O
times	O
.	O
</s>
<s>
Fill	B-General_Concept
characters	I-General_Concept
are	O
usually	O
used	O
in	O
response	O
to	O
some	O
real-world	O
limitation	O
.	O
</s>
<s>
Unlike	O
modern	O
printers	O
,	O
these	O
early	O
printers	O
contained	O
essentially	O
no	O
buffering	O
,	O
nor	O
did	O
they	O
do	O
any	O
handshaking	B-Protocol
,	O
so	O
there	O
would	O
be	O
no	O
place	O
to	O
store	O
the	O
characters	O
which	O
would	O
be	O
received	O
while	O
the	O
printhead	O
was	O
in	O
the	O
process	O
of	O
returning	O
to	O
the	O
left	O
margin	O
,	O
nor	O
any	O
way	O
to	O
tell	O
the	O
sender	O
to	O
temporarily	O
stop	O
transmitting	O
characters	O
.	O
</s>
<s>
Instead	O
,	O
one	O
or	O
more	O
fill	B-General_Concept
characters	I-General_Concept
would	O
be	O
transmitted	O
to	O
cover	O
this	O
time	O
.	O
</s>
<s>
In	O
its	O
strictest	O
definition	O
,	O
fill	B-General_Concept
characters	I-General_Concept
cause	O
no	O
action	O
to	O
be	O
performed	O
at	O
all	O
;	O
they	O
simply	O
consume	O
time	O
.	O
</s>
<s>
The	O
ASCII	B-Protocol
"	O
null	O
"	O
character	O
is	O
commonly	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
In	O
actual	O
practice	O
with	O
printers	O
,	O
though	O
,	O
one	O
of	O
the	O
time	O
slots	O
that	O
would	O
otherwise	O
contain	O
a	O
fill	B-General_Concept
character	I-General_Concept
was	O
usually	O
used	O
to	O
contain	O
the	O
"	O
line-feed	O
"	O
character	O
that	O
caused	O
the	O
paper	O
to	O
advance	O
by	O
one	O
line	O
.	O
</s>
<s>
As	O
described	O
above	O
,	O
printers	O
commonly	O
required	O
fill	B-General_Concept
characters	I-General_Concept
when	O
the	O
carriage	O
was	O
returned	O
to	O
the	O
left	O
margin	O
.	O
</s>
<s>
With	O
other	O
equipment	O
,	O
fill	B-General_Concept
characters	I-General_Concept
were	O
occasionally	O
required	O
in	O
other	O
circumstances	O
.	O
</s>
<s>
For	O
example	O
the	O
VT05	B-Application
video	O
terminal	O
sometimes	O
required	O
fill	B-General_Concept
characters	I-General_Concept
when	O
a	O
"	O
scroll	O
up	O
"	O
operation	O
was	O
performed	O
;	O
the	O
process	O
of	O
shuffling	O
data	O
in	O
the	O
shift	B-General_Concept
register	I-General_Concept
memory	O
of	O
the	O
VT05	B-Application
was	O
slow	O
.	O
</s>
<s>
In	O
a	O
similar	O
fashion	O
,	O
communications	O
protocols	O
often	O
require	O
fill	B-General_Concept
characters	I-General_Concept
at	O
points	O
when	O
processing	O
must	O
be	O
performed	O
.	O
</s>
