<s>
Least	B-General_Concept
Frequently	I-General_Concept
Used	I-General_Concept
(	O
LFU	O
)	O
is	O
a	O
type	O
of	O
cache	B-General_Concept
algorithm	I-General_Concept
used	O
to	O
manage	O
memory	B-General_Concept
within	O
a	O
computer	O
.	O
</s>
<s>
The	O
standard	O
characteristics	O
of	O
this	O
method	O
involve	O
the	O
system	O
keeping	O
track	O
of	O
the	O
number	O
of	O
times	O
a	O
block	B-General_Concept
is	O
referenced	O
in	O
memory	B-General_Concept
.	O
</s>
<s>
When	O
the	O
cache	B-General_Concept
is	O
full	O
and	O
requires	O
more	O
room	O
the	O
system	O
will	O
purge	O
the	O
item	O
with	O
the	O
lowest	O
reference	O
frequency	O
.	O
</s>
<s>
LFU	O
is	O
sometimes	O
combined	O
with	O
a	O
Least	B-General_Concept
Recently	I-General_Concept
Used	I-General_Concept
algorithm	O
and	O
called	O
LRFU	O
.	O
</s>
<s>
The	O
simplest	O
method	O
to	O
employ	O
an	O
LFU	O
algorithm	O
is	O
to	O
assign	O
a	O
counter	O
to	O
every	O
block	B-General_Concept
that	O
is	O
loaded	O
into	O
the	O
cache	B-General_Concept
.	O
</s>
<s>
Each	O
time	O
a	O
reference	O
is	O
made	O
to	O
that	O
block	B-General_Concept
the	O
counter	O
is	O
increased	O
by	O
one	O
.	O
</s>
<s>
When	O
the	O
cache	B-General_Concept
reaches	O
capacity	O
and	O
has	O
a	O
new	O
block	B-General_Concept
waiting	O
to	O
be	O
inserted	O
the	O
system	O
will	O
search	O
for	O
the	O
block	B-General_Concept
with	O
the	O
lowest	O
counter	O
and	O
remove	O
it	O
from	O
the	O
cache	B-General_Concept
.	O
</s>
<s>
Practical	O
LFU	O
:	O
there	O
is	O
a	O
counter	O
for	O
the	O
items	O
stored	O
in	O
cache	B-General_Concept
.	O
</s>
<s>
While	O
the	O
LFU	O
method	O
may	O
seem	O
like	O
an	O
intuitive	O
approach	O
to	O
memory	B-General_Concept
management	O
it	O
is	O
not	O
without	O
faults	O
.	O
</s>
<s>
Consider	O
an	O
item	O
in	O
memory	B-General_Concept
which	O
is	O
referenced	O
repeatedly	O
for	O
a	O
short	O
period	O
of	O
time	O
and	O
is	O
not	O
accessed	O
again	O
for	O
an	O
extended	O
period	O
of	O
time	O
.	O
</s>
<s>
Moreover	O
,	O
new	O
items	O
that	O
just	O
entered	O
the	O
cache	B-General_Concept
are	O
subject	O
to	O
being	O
removed	O
very	O
soon	O
again	O
,	O
because	O
they	O
start	O
with	O
a	O
low	O
counter	O
,	O
even	O
though	O
they	O
might	O
be	O
used	O
very	O
frequently	O
after	O
that	O
.	O
</s>
