<s>
A	O
stub	B-General_Concept
file	I-General_Concept
is	O
a	O
computer	B-Operating_System
file	I-Operating_System
that	O
appears	O
to	O
the	O
user	O
to	O
be	O
on	O
disk	B-Device
and	O
immediately	O
available	O
for	O
use	O
,	O
but	O
is	O
actually	O
held	O
either	O
in	O
part	O
or	O
entirely	O
on	O
a	O
different	O
storage	O
medium	O
.	O
</s>
<s>
When	O
a	O
stub	B-General_Concept
file	I-General_Concept
is	O
accessed	O
,	O
device	B-Application
driver	I-Application
software	O
intercepts	O
the	O
access	O
,	O
retrieves	O
the	O
data	O
from	O
its	O
actual	O
location	O
and	O
writes	O
it	O
to	O
the	O
file	O
,	O
then	O
allows	O
the	O
user	O
's	O
access	O
to	O
proceed	O
.	O
</s>
<s>
File	O
stubbing	O
,	O
the	O
act	O
of	O
creating	O
stub	B-General_Concept
files	I-General_Concept
,	O
is	O
a	O
Hierarchical	B-Application
storage	I-Application
management	I-Application
(	O
HSM	O
)	O
concept	O
.	O
</s>
<s>
The	O
usual	O
purpose	O
of	O
stubbing	O
files	O
is	O
to	O
move	O
data	O
from	O
an	O
expensive	O
high-speed	O
storage	O
device	O
such	O
as	O
a	O
computer	O
's	O
hard	O
drive	O
to	O
lower	O
cost	O
storage	O
such	O
as	O
a	O
magnetic	O
tape	O
,	O
or	O
an	O
electro-optical	O
disk	B-Device
,	O
while	O
not	O
requiring	O
users	O
to	O
know	O
how	O
to	O
use	O
specialised	O
storage	O
software	O
to	O
retrieve	O
the	O
data	O
.	O
</s>
<s>
It	O
also	O
allows	O
a	O
system	B-Application
manager	I-Application
to	O
enforce	O
the	O
use	O
of	O
low	O
cost	O
storage	O
when	O
users	O
would	O
prefer	O
to	O
store	O
their	O
files	O
on	O
the	O
highest	O
availability	O
,	O
and	O
highest	O
cost	O
,	O
media	O
supplied	O
.	O
</s>
<s>
Stubbing	O
is	O
a	O
feature	O
of	O
many	O
commercial	O
file	O
backup	O
and	O
archiving	O
packages	O
and	O
is	O
available	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
Novell	B-Operating_System
NetWare	I-Operating_System
,	O
Linux	B-Application
and	O
other	O
operating	O
systems	O
.	O
</s>
