<s>
.CSO	B-Device
is	O
a	O
compression	B-General_Concept
method	O
for	O
the	O
ISO	B-General_Concept
image	I-General_Concept
format	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
compress	O
dumped	O
PlayStation	B-Operating_System
Portable	I-Operating_System
UMD	O
games	O
,	O
and	O
is	O
an	O
alternative	O
to	O
the	O
.DAX	O
compression	B-General_Concept
method	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
compression	B-General_Concept
method	O
for	O
ISO	B-General_Concept
.	O
</s>
<s>
Booster	O
created	O
the	O
first	O
code	O
;	O
it	O
was	O
later	O
optimized	O
for	O
better	O
compression	B-General_Concept
.	O
</s>
<s>
However	O
at	O
the	O
time	O
,	O
the	O
popular	O
application	O
homebrew	B-Application
"	O
DevHook	B-Device
"	O
used	O
CSO	O
.	O
</s>
<s>
CSO	O
uses	O
Deflate	B-Algorithm
compression	B-General_Concept
with	O
nine	O
levels	O
of	O
presets	O
,	O
usually	O
with	O
2	O
KiB	O
blocks	O
handled	O
individually	O
(	O
they	O
could	O
be	O
uncompressed	B-General_Concept
)	O
.	O
</s>
<s>
While	O
the	O
highest	O
levels	O
of	O
compression	B-General_Concept
can	O
introduce	O
slowdown	O
and	O
lengthy	O
load-times	O
in	O
software	O
which	O
relies	O
heavily	O
on	O
disc	O
streaming	O
,	O
even	O
the	O
lower	O
levels	O
are	O
capable	O
of	O
substantial	O
compression	B-General_Concept
.	O
</s>
<s>
This	O
is	O
partially	O
due	O
to	O
the	O
data	O
layout	O
of	O
a	O
UMD	O
,	O
though	O
more	O
frequently	O
due	O
to	O
the	O
use	O
of	O
Dummy	B-General_Concept
Files	I-General_Concept
as	O
both	O
an	O
anti-piracy	O
tool	O
and	O
a	O
means	O
to	O
more	O
optimally	O
lay	O
the	O
data	O
out	O
physically	O
on	O
the	O
disc	O
.	O
</s>
<s>
In	O
addition	O
to	O
being	O
used	O
for	O
compressing	O
PlayStation	B-Operating_System
Portable	I-Operating_System
UMD	O
games	O
,	O
the	O
PSP	B-Operating_System
port	O
of	O
PicoDrive	O
supports	O
compressed	B-General_Concept
Sega	B-Device
Mega-CD	I-Device
disc	B-Application
images	I-Application
in	O
the	O
CSO	O
format	O
.	O
</s>
<s>
CSO	O
are	O
known	O
to	O
have	O
received	O
later	O
extensions	O
in	O
the	O
form	O
of	O
CSO	O
"	O
v2	O
"	O
and	O
ZSO	O
(	O
"	O
ZISO	O
"	O
)	O
,	O
using	O
LZ4	B-Language
compression	B-General_Concept
for	O
faster	O
decompression	O
.	O
</s>
<s>
DAX	O
is	O
a	O
competing	O
format	O
,	O
it	O
uses	O
8	O
KiB	O
blocks	O
which	O
aims	O
to	O
increase	O
the	O
data	B-General_Concept
compression	I-General_Concept
ratio	I-General_Concept
,	O
and	O
it	O
also	O
allows	O
uncompressed	B-General_Concept
areas	O
just	O
like	O
CSO	O
.	O
</s>
<s>
JSO	O
(	O
"	O
JISO	O
"	O
)	O
was	O
another	O
now	O
unpopular	O
competing	O
format	O
that	O
was	O
overall	O
similar	O
to	O
CSO	O
,	O
with	O
the	O
difference	O
of	O
added	O
option	O
for	O
LZO	B-Language
compression	B-General_Concept
and	O
a	O
block	O
size	O
tweakable	O
in	O
the	O
official	O
compressor	O
.	O
</s>
<s>
Little-endian	O
is	O
assumed	O
for	O
fields	O
larger	O
than	O
a	O
byte	O
,	O
following	O
the	O
architecture	O
endianness	O
of	O
PlayStation	B-Operating_System
Portable	I-Operating_System
.	O
</s>
<s>
0x8	O
Uncompressed	B-General_Concept
size	O
8	O
The	O
size	O
of	O
the	O
original	O
uncompressed	B-General_Concept
ISO	B-General_Concept
in	O
bytes	O
.	O
</s>
<s>
0x10	O
Block	O
size	O
4	O
The	O
size	O
of	O
each	O
data	O
block	O
in	O
bytes	O
before	O
compression	B-General_Concept
.	O
</s>
<s>
Usually	O
2048	O
bytes	O
,	O
same	O
as	O
the	O
size	O
of	O
each	O
ISO	B-Application
9660	I-Application
sector	O
.	O
</s>
<s>
There	O
is	O
an	O
additional	O
,	O
last	O
entry	O
which	O
points	O
to	O
the	O
end	B-Language
of	I-Language
file	I-Language
.	O
</s>
<s>
31	O
1	O
0x80000000	O
Compression	B-General_Concept
type	O
In	O
CSO	O
"	O
v1	O
"	O
format	O
,	O
the	O
meaning	O
of	O
the	O
field	O
is	O
as	O
follows	O
:	O
</s>
<s>
Deflate	B-Algorithm
is	O
used	O
.	O
</s>
<s>
The	O
block	O
is	O
uncompressed	B-General_Concept
.	O
</s>
<s>
The	O
ZSO	O
format	O
has	O
similar	O
semantics	O
,	O
only	O
that	O
0	O
represents	O
LZ4	B-Language
instead	O
of	O
Deflate	B-Algorithm
.	O
</s>
<s>
Deflate	B-Algorithm
is	O
used	O
.	O
</s>
<s>
LZ4	B-Language
is	O
used	O
.	O
</s>
<s>
The	O
block	O
is	O
implicitly	O
considered	O
to	O
be	O
uncompressed	B-General_Concept
if	O
the	O
block	O
size	O
is	O
equal	O
to	O
or	O
larger	O
than	O
the	O
block	O
size	O
specified	O
in	O
the	O
file	O
header	O
.	O
</s>
<s>
Each	O
data	O
block	O
contains	O
uncompressed	B-General_Concept
or	O
compressed	B-General_Concept
data	I-General_Concept
.	O
</s>
<s>
If	O
the	O
index	O
alignment	O
is	O
greater	O
than	O
zero	O
,	O
it	O
is	O
possible	O
that	O
the	O
block	O
size	O
is	O
larger	O
than	O
the	O
data	O
it	O
holds	O
,	O
necessitating	O
the	O
use	O
of	O
padding	B-Application
.	O
</s>
