<s>
Dirhash	B-Application
is	O
a	O
feature	O
of	O
FreeBSD	B-Operating_System
that	O
improves	O
the	O
speed	O
of	O
finding	O
files	O
in	O
a	O
directory	O
.	O
</s>
<s>
Rather	O
than	O
finding	O
a	O
file	O
in	O
a	O
directory	O
using	O
a	O
linear	B-Algorithm
search	I-Algorithm
algorithm	I-Algorithm
,	O
FreeBSD	B-Operating_System
uses	O
a	O
hash	B-Algorithm
table	I-Algorithm
.	O
</s>
<s>
The	O
feature	O
is	O
backwards-compatible	O
because	O
the	O
hash	B-Algorithm
table	I-Algorithm
is	O
built	O
in	O
memory	O
when	O
the	O
directory	O
is	O
accessed	O
,	O
and	O
it	O
does	O
not	O
affect	O
the	O
on-disk	O
format	O
of	O
the	O
filesystem	O
,	O
in	O
contrast	O
to	O
systems	O
such	O
as	O
Htree	B-Library
.	O
</s>
<s>
Dirhash	B-Application
was	O
implemented	O
by	O
Ian	O
Dowse	O
early	O
in	O
2001	O
as	O
an	O
addition	O
to	O
UFS	B-Operating_System
,	O
operating	O
in	O
parallel	O
with	O
higher-level	O
file	O
system	O
caching	O
.	O
</s>
<s>
It	O
was	O
imported	O
into	O
FreeBSD	B-Operating_System
in	O
July	O
2001	O
.	O
</s>
<s>
It	O
was	O
subsequently	O
imported	O
into	O
OpenBSD	B-Operating_System
in	O
December	O
2003	O
and	O
NetBSD	B-Device
in	O
January	O
2005	O
.	O
</s>
