<s>
The	O
USN	B-Application
Journal	I-Application
(	O
Update	O
Sequence	O
Number	O
Journal	O
)	O
,	O
or	O
Change	B-Application
Journal	I-Application
,	O
is	O
a	O
feature	O
of	O
the	O
Windows	O
NT	B-Application
file	I-Application
system	I-Application
(	O
NTFS	B-Application
)	O
which	O
maintains	O
a	O
record	O
of	O
changes	O
made	O
to	O
the	O
volume	B-Application
.	O
</s>
<s>
It	O
is	O
not	O
to	O
be	O
confused	O
with	O
the	O
journal	O
used	O
for	O
the	O
NTFS	B-Application
file	I-Application
system	I-Application
journaling	O
.	O
</s>
<s>
When	O
Windows	B-Application
2000	I-Application
was	O
released	O
,	O
Microsoft	O
created	O
NTFS	B-Application
version	O
3.0	O
,	O
which	O
included	O
several	O
new	O
features	O
and	O
improvements	O
over	O
older	O
versions	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Under	O
Windows	B-Application
2000	I-Application
,	O
NTFS	B-Application
3.0	O
partitions	B-Application
can	O
be	O
set	O
to	O
keep	O
track	O
of	O
changes	O
to	O
files	O
and	O
directories	O
on	O
the	O
volume	B-Application
,	O
providing	O
a	O
record	O
of	O
when	O
and	O
what	O
was	O
done	O
to	O
the	O
various	O
objects	O
.	O
</s>
<s>
When	O
enabled	O
,	O
the	O
system	O
records	O
all	O
changes	O
made	O
to	O
the	O
volume	B-Application
in	O
the	O
USN	B-Application
Journal	I-Application
,	O
which	O
is	O
the	O
name	O
also	O
used	O
to	O
describe	O
the	O
feature	O
itself	O
.	O
</s>
<s>
One	O
journal	O
is	O
maintained	O
for	O
each	O
NTFS	B-Application
volume	B-Application
and	O
stored	O
in	O
the	O
NTFS	B-Application
metafile	O
named	O
$Extend	O
\$UsnJrnl	O
.	O
</s>
<s>
It	O
begins	O
as	O
an	O
empty	O
file	B-Operating_System
.	O
</s>
<s>
Whenever	O
a	O
change	O
is	O
made	O
to	O
the	O
volume	B-Application
,	O
a	O
record	O
is	O
added	O
to	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Each	O
record	O
is	O
identified	O
by	O
a	O
64-bit	B-Device
Update	O
Sequence	O
Number	O
or	O
USN	O
(	O
for	O
this	O
reason	O
Change	B-Application
Journals	I-Application
are	O
sometimes	O
called	O
USN	B-Application
Journals	I-Application
)	O
.	O
</s>
<s>
Each	O
record	O
in	O
the	O
Change	B-Application
Journal	I-Application
contains	O
the	O
USN	O
,	O
the	O
name	O
of	O
the	O
file	B-Operating_System
,	O
and	O
information	O
about	O
what	O
the	O
change	O
was	O
.	O
</s>
<s>
The	O
Change	B-Application
Journal	I-Application
describes	O
the	O
changes	O
that	O
took	O
place	O
using	O
bit	O
flags	O
(	O
e.g.	O
</s>
<s>
For	O
this	O
reason	O
the	O
Change	B-Application
Journal	I-Application
cannot	O
be	O
used	O
to	O
undo	O
operations	O
on	O
files	O
within	O
NTFS	B-Application
.	O
</s>
<s>
The	O
USN	B-Application
Journal	I-Application
is	O
used	O
by	O
the	O
File	B-Operating_System
History	O
feature	O
introduced	O
in	O
Windows	B-Application
8	I-Application
to	O
determine	O
which	O
files	O
have	O
changed	O
since	O
the	O
last	O
backup	O
so	O
that	O
only	O
files	O
that	O
have	O
changed	O
are	O
added	O
to	O
the	O
history	O
so	O
far	O
.	O
</s>
