<s>
A	O
flag	B-General_Concept
day	I-General_Concept
,	O
as	O
used	O
in	O
system	B-Application
administration	I-Application
,	O
is	O
a	O
change	O
which	O
requires	O
a	O
complete	O
restart	O
or	O
conversion	O
of	O
a	O
sizable	O
body	O
of	O
software	O
or	O
data	O
.	O
</s>
<s>
The	O
situation	O
may	O
arise	O
if	O
there	O
are	O
limitations	O
on	O
backward	B-General_Concept
compatibility	I-General_Concept
and	O
forward	B-General_Concept
compatibility	I-General_Concept
among	O
system	O
components	O
,	O
which	O
then	O
requires	O
that	O
updates	O
be	O
performed	O
almost	O
simultaneously	O
(	O
during	O
a	O
"	O
flag	B-General_Concept
day	I-General_Concept
cutover	O
"	O
)	O
for	O
the	O
system	O
to	O
function	O
after	O
the	O
upgrade	O
.	O
</s>
<s>
This	O
systems	O
terminology	O
originates	O
from	O
a	O
major	O
change	O
in	O
the	O
Multics	B-Application
operating	I-Application
system	I-Application
's	O
definition	O
of	O
ASCII	B-Protocol
,	O
which	O
was	O
scheduled	O
for	O
the	O
United	O
States	O
holiday	O
,	O
Flag	B-General_Concept
Day	I-General_Concept
,	O
on	O
June	O
14	O
,	O
1966	O
.	O
</s>
<s>
Another	O
historical	O
flag	B-General_Concept
day	I-General_Concept
was	O
January	O
1	O
,	O
1983	O
,	O
when	O
the	O
ARPANET	O
changed	O
from	O
NCP	B-Protocol
to	O
the	O
TCP/IP	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
