<s>
Symmetry	O
and	O
asymmetry	O
,	O
in	O
the	O
context	O
of	O
data	B-General_Concept
compression	I-General_Concept
,	O
refer	O
to	O
the	O
time	O
relation	O
between	O
compression	O
and	O
decompression	O
for	O
a	O
given	O
compression	B-General_Concept
algorithm	I-General_Concept
.	O
</s>
<s>
Note	O
that	O
compression	O
and	O
decompression	O
,	O
even	O
for	O
a	O
symmetric	O
algorithm	O
,	O
may	O
not	O
be	O
perfectly	O
symmetric	O
in	O
practice	O
,	O
depending	O
on	O
the	O
devices	O
the	O
data	O
is	O
being	O
copied	O
to	O
and	O
from	O
,	O
and	O
other	O
factors	O
such	O
as	O
latency	O
and	O
the	O
fragmentation	B-Architecture
on	O
the	O
device	O
.	O
</s>
<s>
Asymmetrical	O
algorithms	O
wherein	O
the	O
compression	O
is	O
faster	O
than	O
the	O
decompression	O
can	O
be	O
useful	O
for	O
backing	B-Protocol
up	I-Protocol
or	O
archiving	O
data	O
,	O
as	O
in	O
these	O
cases	O
data	O
is	O
typically	O
much	O
more	O
often	O
stored	O
than	O
retrieved	O
.	O
</s>
