<s>
ZPAQ	B-Application
is	O
an	O
open	B-Application
source	I-Application
command	B-Application
line	I-Application
archiver	O
for	O
Windows	B-Application
and	O
Linux	B-Application
.	O
</s>
<s>
It	O
compresses	O
using	O
deduplication	B-General_Concept
and	O
several	O
algorithms	O
(	O
LZ77	O
,	O
BWT	B-Algorithm
,	O
and	O
context	B-General_Concept
mixing	I-General_Concept
)	O
depending	O
on	O
the	O
data	O
type	O
and	O
the	O
selected	O
compression	O
level	O
.	O
</s>
<s>
The	O
ZPAQ	B-Application
source	O
code	O
includes	O
a	O
public	O
domain	O
API	B-General_Concept
,	O
libzpaq	O
,	O
which	O
provides	O
compression	O
and	O
decompression	O
services	O
to	O
C++	B-Language
applications	O
.	O
</s>
<s>
Files	O
are	O
saved	O
in	O
the	O
ZPAQ	B-Application
level	O
2	O
journaling	O
format	O
.	O
</s>
<s>
Only	O
the	O
journaling	O
format	O
supports	O
deduplication	B-General_Concept
,	O
directory	O
attributes	O
,	O
and	O
multiple	O
dated	O
file	O
versions	O
.	O
</s>
<s>
Each	O
segment	O
has	O
a	O
header	O
containing	O
an	O
optional	O
file	O
name	O
and	O
an	O
optional	O
comment	O
for	O
meta-data	O
such	O
as	O
size	O
,	O
date	O
,	O
and	O
attributes	O
,	O
and	O
an	O
optional	O
trailing	O
SHA-1	B-Algorithm
checksum	O
of	O
the	O
original	O
data	O
for	O
integrity	O
checking	O
.	O
</s>
<s>
The	O
fragment	O
tables	O
give	O
the	O
size	O
and	O
SHA-1	B-Algorithm
hash	I-Algorithm
of	O
each	O
fragment	O
.	O
</s>
<s>
The	O
ZPAQ	B-Application
standard	O
does	O
not	O
specify	O
a	O
compression	O
algorithm	O
.	O
</s>
<s>
The	O
COMP	O
models	O
are	O
based	O
on	O
PAQ	B-Application
,	O
which	O
compresses	O
one	O
bit	O
at	O
a	O
time	O
using	O
arithmetic	B-Algorithm
coding	I-Algorithm
.	O
</s>
<s>
On	O
update	O
,	O
ZPAQ	B-Application
divides	O
the	O
input	O
files	O
into	O
fragments	O
,	O
computes	O
their	O
SHA-1	B-Algorithm
hashes	I-Algorithm
,	O
and	O
compares	O
them	O
to	O
the	O
hashes	O
stored	O
in	O
the	O
archive	O
.	O
</s>
<s>
Rather	O
than	O
a	O
Rabin	B-Algorithm
fingerprint	I-Algorithm
,	O
ZPAQ	B-Application
uses	O
a	O
rolling	B-Error_Name
hash	I-Error_Name
that	O
depends	O
on	O
the	O
last	O
32	O
bytes	O
that	O
are	O
not	O
predicted	O
by	O
an	O
order	O
1	O
context	O
,	O
plus	O
any	O
predicted	O
bytes	O
in	O
between	O
.	O
</s>
<s>
The	O
rolling	B-Error_Name
hash	I-Error_Name
uses	O
a	O
256	O
byte	O
table	O
containing	O
the	O
byte	O
last	O
seen	O
in	O
each	O
possible	O
order-1	O
context	O
.	O
</s>
<s>
ZPAQ	B-Application
has	O
5	O
compression	O
levels	O
,	O
from	O
fastest	O
to	O
best	O
.	O
</s>
<s>
At	O
all	O
but	O
the	O
best	O
level	O
,	O
it	O
uses	O
the	O
statistics	O
of	O
the	O
order-1	O
prediction	O
table	O
used	O
for	O
deduplication	B-General_Concept
to	O
test	O
whether	O
the	O
input	O
appears	O
random	O
.	O
</s>
<s>
ZPAQ	B-Application
will	O
use	O
an	O
E8E9	O
transform	O
(	O
see	O
:	O
BCJ	B-Algorithm
)	O
to	O
improve	O
the	O
compression	O
of	O
x86	O
code	O
typically	O
found	O
in	O
.exe	O
and	O
.dll	O
files	O
.	O
</s>
<s>
ZPAQ	B-Application
lacks	O
error	O
correction	O
but	O
has	O
several	O
features	O
that	O
limit	O
damage	O
if	O
the	O
archive	O
is	O
corrupted	O
.	O
</s>
<s>
On	O
decompression	O
,	O
all	O
SHA-1	B-Algorithm
hashes	I-Algorithm
are	O
checked	O
.	O
</s>
<s>
If	O
an	O
update	O
is	O
interrupted	O
,	O
then	O
the	O
temporary	O
header	O
signals	O
ZPAQ	B-Application
that	O
no	O
useful	O
data	O
is	O
found	O
after	O
it	O
.	O
</s>
<s>
The	O
options	O
-mX	O
(	O
with	O
X	O
being	O
the	O
compression	O
level	O
from	O
0	O
to	O
5	O
)	O
and	O
-key	O
(	O
which	O
performs	O
AES-256	B-Algorithm
encryption	O
)	O
can	O
be	O
omitted	O
.	O
</s>
<s>
The	O
0	O
compression	O
level	O
does	O
not	O
compress	O
data	O
,	O
but	O
still	O
carries	O
out	O
data	B-General_Concept
deduplication	I-General_Concept
.	O
</s>
<s>
zpaq	B-Application
list	O
archive.zpaq	O
lists	O
the	O
files	O
and	O
directories	O
of	O
the	O
most	O
recent	O
version	O
.	O
</s>
<s>
The	O
output	O
can	O
be	O
further	O
processed	O
with	O
grep	B-Application
and	O
other	O
tools	O
.	O
</s>
<s>
zpaq	B-Application
extract	O
archive.zpaq	O
will	O
un-pack	O
the	O
last	O
version	O
of	O
the	O
entire	O
archive	O
in	O
the	O
active	O
directory	O
.	O
</s>
<s>
zpaq	B-Application
extract	O
backup.zpaq	O
path	O
will	O
only	O
extract	O
the	O
specified	O
directory	O
(	O
or	O
file	O
)	O
.	O
</s>
<s>
The	O
optional	O
-to	O
tells	O
ZPAQ	B-Application
where	O
to	O
save	O
the	O
extracted	O
files	O
.	O
</s>
<s>
zpaq	B-Application
extract	O
backup.zpaq	O
-all	O
-only	O
"	O
*	O
muppet*	O
"	O
will	O
extract	O
all	O
versions	O
of	O
all	O
files	O
and	O
directories	O
whose	O
name	O
contains	O
"	O
muppet	O
"	O
.	O
</s>
<s>
Feb	O
.	O
15	O
,	O
2009	O
-	O
zpaq	B-Application
0.01	O
experimental	O
release	O
.	O
</s>
<s>
12	O
,	O
2009	O
-	O
zpaq	B-Application
1.00	O
specification	O
finalized	O
guaranteeing	O
backward	O
compatibility	O
.	O
</s>
<s>
Sept	O
.	O
29	O
,	O
2009	O
-	O
zpaq	B-Application
1.06	O
,	O
specification	O
updated	O
to	O
v1.01	O
add	O
locator	O
tags	O
to	O
support	O
self	O
extracting	O
archives	O
.	O
</s>
<s>
Oct	O
.	O
14	O
,	O
2009	O
-	O
zpaq	B-Application
1.09	O
adds	O
ZPAQL	O
to	O
C++	B-Language
translator	O
as	O
a	O
speed	O
optimization	O
.	O
</s>
<s>
Sept	O
.	O
27	O
,	O
2010	O
-	O
separate	O
libzpaq	O
0.01	O
API	B-General_Concept
.	O
</s>
<s>
Jan	O
.	O
21	O
,	O
2011	O
-	O
pzpaq	O
0.01	O
,	O
first	O
multi-threaded	O
version	O
,	O
later	O
incorporated	O
back	O
into	O
zpaq	B-Application
.	O
</s>
<s>
Nov	O
.	O
13	O
,	O
2011	O
-	O
zpaq	B-Application
4.00	O
,	O
adds	O
JIT	O
compiler	O
(	O
ZPAQL	O
to	O
x86	O
)	O
eliminating	O
need	O
for	O
external	O
C++	B-Language
compiler	O
for	O
optimization	O
.	O
</s>
<s>
Feb	O
.	O
1	O
,	O
2012	O
-	O
zpaq	B-Application
5.00	O
,	O
specification	O
updated	O
to	O
v2.00	O
to	O
allow	O
empty	O
COMP	O
section	O
(	O
post-processing	O
only	O
)	O
.	O
</s>
<s>
Sept	O
.	O
28	O
,	O
2012	O
-	O
zpaq	B-Application
6.00	O
,	O
specification	O
updated	O
to	O
v2.01	O
adding	O
journaling	O
format	O
.	O
</s>
<s>
Jan	O
.	O
23	O
,	O
2013	O
-	O
zpaq	B-Application
6.19	O
,	O
splits	O
development	O
functions	O
to	O
a	O
separate	O
program	O
,	O
zpaqd	O
.	O
</s>
<s>
,	O
a	O
compression	O
abstraction	O
layer	O
supporting	O
many	O
codecs	B-General_Concept
.	O
</s>
<s>
,	O
an	O
archiver	O
supporting	O
over	O
150	O
formats	O
including	O
ZPAQ	B-Application
streaming	O
format	O
extraction	O
.	O
</s>
