<s>
In	O
computing	O
,	O
file	B-Application
comparison	I-Application
is	O
the	O
calculation	O
and	O
display	O
of	O
the	O
differences	O
and	O
similarities	O
between	O
data	O
objects	O
,	O
typically	O
text	B-General_Concept
files	I-General_Concept
such	O
as	O
source	O
code	O
.	O
</s>
<s>
The	O
methods	O
,	O
implementations	O
,	O
and	O
results	O
are	O
typically	O
called	O
a	O
diff	B-Application
,	O
after	O
the	O
Unix	B-Application
diff	B-Application
utility	I-Application
.	O
</s>
<s>
The	O
output	O
may	O
be	O
presented	O
in	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
or	O
used	O
as	O
part	O
of	O
larger	O
tasks	O
in	O
networks	B-Architecture
,	O
file	B-Application
systems	I-Application
,	O
or	O
revision	B-Architecture
control	I-Architecture
.	O
</s>
<s>
Some	O
widely	O
used	O
file	B-Application
comparison	I-Application
programs	O
are	O
diff	B-Application
,	O
cmp	B-Application
,	O
FileMerge	O
,	O
WinMerge	B-Language
,	O
Beyond	B-Language
Compare	I-Language
,	O
and	O
File	B-Device
Compare	I-Device
.	O
</s>
<s>
Many	O
text	B-Application
editors	I-Application
and	O
word	B-General_Concept
processors	I-General_Concept
perform	O
file	B-Application
comparison	I-Application
to	O
highlight	O
the	O
changes	O
to	O
a	O
file	O
or	O
document	O
.	O
</s>
<s>
Most	O
file	B-Application
comparison	I-Application
tools	O
find	O
the	O
longest	O
common	O
subsequence	O
between	O
two	O
files	O
.	O
</s>
<s>
This	O
is	O
used	O
in	O
the	O
IBM	B-General_Concept
History	I-General_Concept
Flow	I-General_Concept
tool	I-General_Concept
.	O
</s>
<s>
Other	O
file	B-Application
comparison	I-Application
programs	O
find	O
block	O
moves	O
.	O
</s>
<s>
Some	O
specialized	O
file	B-Application
comparison	I-Application
tools	O
find	O
the	O
longest	O
increasing	O
subsequence	O
between	O
two	O
files	O
.	O
</s>
<s>
The	O
rsync	B-Application
protocol	O
uses	O
a	O
rolling	B-Error_Name
hash	I-Error_Name
function	O
to	O
compare	O
two	O
files	O
on	O
two	O
distant	O
computers	O
with	O
low	O
communication	O
overhead	O
.	O
</s>
<s>
File	B-Application
comparison	I-Application
in	O
word	B-General_Concept
processors	I-General_Concept
is	O
typically	O
at	O
the	O
word	O
level	O
,	O
while	O
comparison	O
in	O
most	O
programming	O
tools	O
is	O
at	O
the	O
line	O
level	O
.	O
</s>
<s>
Display	O
of	O
file	B-Application
comparison	I-Application
varies	O
,	O
with	O
the	O
main	O
approaches	O
being	O
either	O
showing	O
two	O
files	O
side-by-side	O
,	O
or	O
showing	O
a	O
single	O
file	O
,	O
with	O
markup	O
showing	O
the	O
changes	O
from	O
one	O
file	O
to	O
the	O
other	O
.	O
</s>
<s>
In	O
either	O
case	O
,	O
particularly	O
side-by-side	O
viewing	O
,	O
code	B-Application
folding	I-Application
or	O
text	B-Application
folding	I-Application
may	O
be	O
used	O
to	O
hide	O
unchanged	O
portions	O
of	O
the	O
file	O
,	O
only	O
showing	O
the	O
changed	O
portions	O
.	O
</s>
<s>
But	O
if	O
one	O
wishes	O
to	O
compare	O
text	B-General_Concept
files	I-General_Concept
or	O
computer	B-Application
programs	I-Application
,	O
a	O
side-by-side	O
visual	O
comparison	O
is	O
usually	O
best	O
.	O
</s>
<s>
File	B-Application
comparison	I-Application
is	O
an	O
important	O
,	O
and	O
most	O
likely	O
integral	O
,	O
part	O
of	O
file	B-Application
synchronization	I-Application
and	O
backup	B-Protocol
.	O
</s>
<s>
In	O
backup	B-Protocol
methodologies	O
,	O
the	O
issue	O
of	O
data	O
corruption	O
is	O
an	O
important	O
one	O
.	O
</s>
<s>
Therefore	O
,	O
all	O
file	B-Application
sync	I-Application
or	O
backup	B-Protocol
programs	O
must	O
include	O
file	B-Application
comparison	I-Application
if	O
these	O
programs	O
are	O
to	O
be	O
actually	O
useful	O
and	O
trusted	O
.	O
</s>
<s>
Prior	O
to	O
file	B-Application
comparison	I-Application
,	O
machines	O
existed	O
to	O
compare	O
magnetic	O
tapes	O
or	O
punch	B-Architecture
cards	I-Architecture
.	O
</s>
<s>
The	O
IBM	O
519	O
Card	O
Reproducer	O
could	O
determine	O
whether	O
a	O
deck	O
of	O
punched	B-Architecture
cards	I-Architecture
were	O
equivalent	O
.	O
</s>
<s>
In	O
1957	O
,	O
John	O
Van	O
Gardner	O
developed	O
a	O
system	O
to	O
compare	O
the	O
check	B-Algorithm
sums	I-Algorithm
of	O
loaded	O
sections	O
of	O
Fortran	B-Application
programs	O
to	O
debug	O
compilation	O
problems	O
on	O
the	O
IBM	B-Device
704	I-Device
.	O
</s>
