<s>
In	O
computing	O
,	O
a	O
Personal	B-Operating_System
Storage	I-Operating_System
Table	I-Operating_System
(	O
.pst	B-Operating_System
)	O
is	O
an	O
open	O
proprietary	O
file	O
format	O
used	O
to	O
store	O
copies	O
of	O
messages	O
,	O
calendar	O
events	O
,	O
and	O
other	O
items	O
within	O
Microsoft	O
software	O
such	O
as	O
Microsoft	B-Application
Exchange	I-Application
Client	I-Application
,	O
Windows	B-Application
Messaging	I-Application
,	O
and	O
Microsoft	B-Application
Outlook	I-Application
.	O
</s>
<s>
The	O
file	O
format	O
may	O
also	O
be	O
known	O
as	O
a	O
Personal	B-Operating_System
Folders	I-Operating_System
(	O
File	O
)	O
or	O
Post	O
Office	O
File	O
.	O
</s>
<s>
When	O
functioning	O
in	O
its	O
capacity	O
as	O
a	O
cache	O
for	O
Outlook	O
's	O
Cached	O
Exchange	O
Mode	O
feature	O
,	O
it	O
may	O
be	O
called	O
an	O
Off-line	O
Storage	O
Table	O
(	O
.ost	B-Operating_System
)	O
or	O
an	O
Off-line	O
Folders	O
(	O
File	O
)	O
.	O
</s>
<s>
In	O
Microsoft	B-Operating_System
Exchange	I-Operating_System
Server	I-Operating_System
,	O
the	O
messages	O
,	O
the	O
calendar	O
,	O
and	O
other	O
data	O
items	O
are	O
delivered	O
to	O
and	O
stored	O
on	O
the	O
server	B-Application
.	O
</s>
<s>
Microsoft	B-Application
Outlook	I-Application
stores	O
these	O
items	O
in	O
a	O
personal-storage-table	O
(	O
.pst	B-Operating_System
)	O
or	O
off-line-storage-table	O
(	O
.ost	B-Operating_System
)	O
files	O
that	O
are	O
located	O
on	O
the	O
local	O
computer	O
.	O
</s>
<s>
Most	O
commonly	O
,	O
the	O
.pst	B-Operating_System
files	O
are	O
used	O
to	O
store	O
archived	O
items	O
and	O
the	O
.ost	B-Operating_System
files	O
to	O
maintain	O
off-line	O
availability	O
of	O
the	O
items	O
.	O
</s>
<s>
This	O
is	O
an	O
essential	O
feature	O
of	O
Microsoft	B-Application
Outlook	I-Application
.	O
</s>
<s>
The	O
size	O
of	O
these	O
files	O
no	O
longer	O
counts	O
against	O
the	O
size	O
of	O
the	O
mailbox	O
used	O
;	O
by	O
moving	O
files	O
from	O
a	O
server	B-Application
mailbox	O
to	O
.pst	B-Operating_System
files	O
,	O
users	O
can	O
free	O
storage	O
space	O
on	O
their	O
mailservers	O
.	O
</s>
<s>
To	O
use	O
the	O
.pst	B-Operating_System
files	O
from	O
another	O
location	O
the	O
user	O
needs	O
to	O
be	O
able	O
to	O
access	O
the	O
files	O
directly	O
over	O
a	O
network	O
from	O
their	O
mail	O
client	O
.	O
</s>
<s>
While	O
it	O
is	O
possible	O
to	O
open	O
and	O
use	O
a	O
.pst	B-Operating_System
file	O
from	O
over	O
a	O
network	O
,	O
this	O
is	O
unsupported	O
,	O
and	O
Microsoft	O
advises	O
against	O
it	O
,	O
as	O
.pst	B-Operating_System
files	O
are	O
prone	O
to	O
corruption	O
when	O
used	O
in	O
this	O
manner	O
.	O
</s>
<s>
Both	O
the	O
.pst	B-Operating_System
and	O
.ost	B-Operating_System
files	O
use	O
a	O
fixed-block-based	O
allocation	O
scheme	O
;	O
the	O
file	O
is	O
enlarged	O
by	O
a	O
fixed	O
amount	O
of	O
bytes	O
,	O
and	O
the	O
file	O
internally	O
maintains	O
information	O
about	O
the	O
allocated	O
and	O
non-allocated	O
blocks	O
.	O
</s>
<s>
So	O
,	O
when	O
data	O
files	O
like	O
email	O
messages	O
are	O
added	O
to	O
a	O
.pst	B-Operating_System
file	O
,	O
its	O
file	O
size	O
is	O
automatically	O
adjusted	O
by	O
the	O
mail	O
client	O
(	O
if	O
necessary	O
)	O
.	O
</s>
<s>
When	O
mail	O
is	O
deleted	O
from	O
a	O
.pst	B-Operating_System
file	O
,	O
the	O
size	O
of	O
the	O
.pst	B-Operating_System
file	O
will	O
stay	O
the	O
same	O
,	O
marking	O
the	O
space	O
as	O
unallocated	O
so	O
that	O
it	O
will	O
hold	O
future	O
data	O
items	O
.	O
</s>
<s>
Recently	O
removed	O
data	O
items	O
can	O
actually	O
be	O
recovered	O
from	O
.pst	B-Operating_System
and	O
.ost	B-Operating_System
files	O
.	O
</s>
<s>
To	O
reduce	O
the	O
size	O
of	O
.pst	B-Operating_System
files	O
,	O
the	O
user	O
needs	O
to	O
compact	O
them	O
.	O
</s>
<s>
Password	O
protection	O
can	O
be	O
used	O
to	O
protect	O
the	O
content	O
of	O
the	O
.pst	B-Operating_System
files	O
.	O
</s>
<s>
in	O
the	O
.pst	B-Operating_System
file	O
.	O
</s>
<s>
None	O
the	O
.pst	B-Operating_System
data	O
is	O
stored	O
as	O
plain	O
text	O
.	O
</s>
<s>
Compressible	O
the	O
.pst	B-Operating_System
data	O
is	O
encrypted	O
with	O
a	O
byte-substitution	O
cipher	B-Application
with	O
a	O
fixed	O
substitution	O
table	O
.	O
</s>
<s>
High	O
(	O
sometimes	O
called	O
"	O
better	O
"	O
)	O
encryption	O
is	O
similar	O
to	O
a	O
WWII	O
German	O
Enigma	O
cipher	B-Application
with	O
three	O
fixed	O
rotors	O
.	O
</s>
<s>
The	O
.pst	B-Operating_System
file	O
format	O
is	O
supported	O
by	O
several	O
Microsoft	O
client	O
applications	O
,	O
including	O
Microsoft	B-Application
Exchange	I-Application
Client	I-Application
,	O
Windows	B-Application
Messaging	I-Application
,	O
and	O
Microsoft	B-Application
Outlook	I-Application
;	O
in	O
the	O
previous	O
two	O
,	O
it	O
was	O
often	O
used	O
with	O
a	O
Personal	O
Address	O
Book	O
(	O
.pab	O
)	O
file	O
,	O
which	O
stores	O
address	O
book	O
.	O
</s>
<s>
The	O
includes	O
tools	O
to	O
convert	O
.pst	B-Operating_System
files	O
into	O
open	O
formats	O
such	O
as	O
mbox	B-Application
and	O
LDAP	O
Data	O
Interchange	O
Format	O
.	O
</s>
<s>
libpst	O
is	O
licensed	O
under	O
the	O
GPL	B-License
and	O
is	O
now	O
included	O
in	O
Fedora	O
10	O
.	O
is	O
a	O
commercially	O
licensed	O
COM	O
Component	O
that	O
provides	O
access	O
to	O
.pst	B-Operating_System
files	O
without	O
MAPI	O
.	O
</s>
<s>
There	O
are	O
tools	O
to	O
convert	O
.pst	B-Operating_System
to	O
other	O
formats	O
or	O
to	O
upload	O
to	O
other	O
online	O
e-mails	O
like	O
Gmail	O
,	O
for	O
example	O
.	O
</s>
<s>
The	O
file	O
is	O
structured	O
as	O
a	O
B-tree	B-Architecture
with	O
512	O
byte	O
nodes	O
and	O
leaves	O
.	O
</s>
<s>
All	O
PST	B-Operating_System
files	I-Operating_System
begin	O
with	O
the	O
four-byte	O
magic	O
string	O
"	O
!	O
BDN	O
"	O
,	O
a	O
four-byte	O
CRC	O
number	O
,	O
and	O
a	O
two-byte	O
magic	O
string	O
of	O
"	O
SM	O
"	O
.	O
</s>
<s>
Outlook	B-Application
2002	I-Application
and	O
earlier	O
use	O
ANSI	O
(	O
extended	O
ASCII	O
with	O
a	O
codepage	O
)	O
encoding	O
for	O
their	O
.pst	B-Operating_System
and	O
.ost	B-Operating_System
files	O
.	O
</s>
<s>
A	O
file	O
exceeding	O
this	O
size	O
is	O
likely	O
to	O
give	O
error	O
messages	O
,	O
such	O
as	O
"	O
.pst	B-Operating_System
has	O
reached	O
maximum	O
size	O
limit	O
,	O
"	O
and	O
could	O
become	O
corrupted	O
.	O
</s>
<s>
From	O
Outlook	B-Application
2003	I-Application
and	O
onward	O
,	O
the	O
new	O
standard	O
format	O
for	O
.pst	B-Operating_System
and	O
.ost	B-Operating_System
files	O
is	O
Unicode	O
(	O
UTF-16	O
little-endian	O
)	O
,	O
with	O
64-bit	O
pointers	O
instead	O
of	O
32-bit	O
to	O
allow	O
larger	O
than	O
2	O
GiB	O
sizes	O
.	O
</s>
<s>
A	O
file	O
that	O
is	O
created	O
in	O
the	O
personal-folders	O
format	O
in	O
Outlook	B-Application
2003	I-Application
or	O
later	O
is	O
not	O
compatible	O
and	O
cannot	O
be	O
opened	O
by	O
earlier	O
versions	O
.	O
</s>
<s>
As	O
with	O
any	O
file	O
,	O
.pst	B-Operating_System
files	O
can	O
become	O
corrupted	O
.	O
</s>
<s>
Growth	O
over	O
the	O
limit	O
has	O
been	O
a	O
consistent	O
problem	O
;	O
ANSI	O
.pst	B-Operating_System
that	O
grew	O
beyond	O
2	O
GiB	O
and	O
Unicode	O
.pst	B-Operating_System
that	O
grew	O
beyond	O
20	O
or	O
50	O
GB	O
would	O
become	O
unusable	O
.	O
</s>
<s>
The	O
scanpst.exe	O
tool	O
has	O
been	O
included	O
with	O
all	O
versions	O
of	O
Outlook	O
to	O
detect	O
and	O
repair	O
.pst	B-Operating_System
database	O
corruption	O
,	O
and	O
Microsoft	O
at	O
one	O
point	O
offered	O
a	O
special-purpose	O
PST2GB	O
that	O
would	O
simply	O
truncate	O
the	O
file	O
to	O
2	O
GiB	O
to	O
allow	O
Outlook	O
to	O
repair	O
it	O
.	O
</s>
<s>
Microsoft	B-Application
Entourage	I-Application
was	O
Microsoft	O
's	O
email	O
and	O
personal	O
information	O
program	O
for	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
(	O
replaced	O
by	O
Outlook	B-Application
for	I-Application
Macintosh	I-Application
in	O
Microsoft	B-Operating_System
Office	I-Operating_System
for	I-Operating_System
Mac	I-Operating_System
2011	I-Operating_System
)	O
.	O
</s>
<s>
Entourage	B-Application
2008	I-Application
,	O
the	O
current	O
version	O
as	O
of	O
May	O
2010	O
,	O
has	O
no	O
support	O
for	O
.pst	B-Operating_System
files	O
,	O
though	O
there	O
exists	O
Microsoft	O
's	O
.pst	B-Operating_System
import	O
tool	O
for	O
Entourage	O
2004	O
;	O
however	O
,	O
the	O
tool	O
could	O
only	O
import	O
.pst	B-Operating_System
files	O
from	O
Outlook	O
for	O
Mac	O
2001	O
,	O
and	O
not	O
any	O
Windows	O
versions	O
.	O
</s>
<s>
Entourage	O
's	O
replacement	O
,	O
Outlook	O
for	O
Office	B-Operating_System
2011	I-Operating_System
for	O
Intel	O
Macs	O
,	O
was	O
able	O
to	O
import	O
Outlook	O
.pst	B-Operating_System
files	O
from	O
Windows	O
;	O
however	O
,	O
data	O
will	O
be	O
stored	O
as	O
many	O
individual	O
files	O
,	O
rather	O
than	O
in	O
a	O
single	O
database	O
such	O
as	O
.pst	B-Operating_System
or	O
the	O
Entourage	O
database	O
.	O
</s>
<s>
Outlook	O
for	O
Mac	O
2001	O
,	O
which	O
runs	O
under	O
Mac	O
OS	O
9	O
or	O
the	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
Classic	O
Environment	O
,	O
connects	O
exclusively	O
to	O
Exchange	B-Operating_System
servers	I-Operating_System
,	O
and	O
to	O
this	O
day	O
is	O
closer	O
to	O
its	O
Windows	O
counterpart	O
than	O
Entourage	O
is	O
.	O
</s>
<s>
It	O
works	O
directly	O
with	O
'	O
Outlook	O
97-2002	O
'	O
.pst	B-Operating_System
files	O
,	O
and	O
can	O
freely	O
interchange	O
those	O
files	O
with	O
Outlook	O
for	O
Windows	O
,	O
as	O
recent	O
versions	O
are	O
still	O
compatible	O
with	O
the	O
older	O
.pst	B-Operating_System
format	O
.	O
</s>
<s>
The	O
limit	O
for	O
Outlook	B-Application
2011	I-Application
is	O
10GB	O
.	O
</s>
