<s>
A	O
CD-ROM	B-Device
(	O
,	O
compact	B-Device
disc	I-Device
read-only	I-Device
memory	I-Device
)	O
is	O
a	O
type	O
of	O
read-only	B-Device
memory	I-Device
consisting	O
of	O
a	O
pre-pressed	O
optical	O
compact	O
disc	O
that	O
contains	O
data	B-General_Concept
.	O
</s>
<s>
Computers	O
can	O
read	O
—	O
but	O
not	O
write	O
or	O
erase	O
—	O
CD-ROMs	B-Device
.	O
</s>
<s>
Some	O
CDs	O
,	O
called	O
enhanced	O
CDs	O
,	O
hold	O
both	O
computer	O
data	B-General_Concept
and	O
audio	O
with	O
the	O
latter	O
capable	O
of	O
being	O
played	O
on	O
a	O
CD	B-Device
player	I-Device
,	O
while	O
data	B-General_Concept
(	O
such	O
as	O
software	O
or	O
digital	O
video	O
)	O
is	O
only	O
usable	O
on	O
a	O
computer	O
(	O
such	O
as	O
ISO	B-Application
9660	I-Application
format	O
PC	B-Device
CD-ROMs	I-Device
)	O
.	O
</s>
<s>
During	O
the	O
1990s	O
and	O
early	O
2000s	O
,	O
CD-ROMs	B-Device
were	O
popularly	O
used	O
to	O
distribute	O
software	O
and	O
data	B-General_Concept
for	O
computers	O
and	O
fifth	B-Application
generation	I-Application
video	I-Application
game	I-Application
consoles	I-Application
.	O
</s>
<s>
The	O
earliest	O
theoretical	O
work	O
on	O
optical	B-Device
disc	I-Device
storage	O
was	O
done	O
by	O
independent	O
researchers	O
in	O
the	O
United	O
States	O
including	O
David	O
Paul	O
Gregg	O
(	O
1958	O
)	O
and	O
James	O
Russel	O
(	O
1965	O
–	O
1975	O
)	O
.	O
</s>
<s>
Key	O
work	O
to	O
digitize	O
the	O
optical	B-Device
disc	I-Device
was	O
performed	O
by	O
Toshi	O
Doi	O
and	O
Kees	O
Schouhamer	O
Immink	O
during	O
1979	O
–	O
1980	O
,	O
who	O
worked	O
on	O
a	O
taskforce	O
for	O
Sony	O
and	O
Phillips	O
.	O
</s>
<s>
The	O
CD-ROM	B-Device
was	O
later	O
designed	O
as	O
an	O
extension	O
of	O
the	O
CD-DA	O
,	O
and	O
adapted	O
this	O
format	O
to	O
hold	O
any	O
form	O
of	O
digital	O
data	B-General_Concept
,	O
with	O
an	O
initial	O
storage	B-General_Concept
capacity	I-General_Concept
of	O
553	O
MB	O
.	O
</s>
<s>
Sony	O
and	O
Philips	O
created	O
the	O
technical	O
standard	O
that	O
defines	O
the	O
format	O
of	O
a	O
CD-ROM	B-Device
in	O
1983	O
,	O
in	O
what	O
came	O
to	O
be	O
called	O
the	O
Yellow	B-Device
Book	I-Device
.	O
</s>
<s>
The	O
CD-ROM	B-Device
was	O
announced	O
in	O
1984	O
and	O
introduced	O
by	O
Denon	O
and	O
Sony	O
at	O
the	O
first	O
Japanese	O
COMDEX	O
computer	O
show	O
in	O
1985	O
.	O
</s>
<s>
In	O
November	O
,	O
1985	O
,	O
several	O
computer	O
industry	O
participants	O
including	O
Microsoft	O
,	O
Philips	O
,	O
Sony	O
,	O
Apple	O
and	O
Digital	O
Equipment	O
Corporation	O
met	O
to	O
create	O
a	O
specification	O
to	O
define	O
a	O
file	B-Application
system	I-Application
format	O
for	O
CD-ROMs	B-Device
.	O
</s>
<s>
It	O
was	O
eventually	O
standardized	O
,	O
with	O
a	O
few	O
changes	O
,	O
as	O
the	O
ISO	B-Application
9660	I-Application
standard	O
in	O
1988	O
.	O
</s>
<s>
One	O
of	O
the	O
first	O
CD-ROM	B-Device
products	O
to	O
be	O
made	O
available	O
to	O
the	O
public	O
was	O
the	O
Grolier	O
Academic	O
Encyclopedia	O
,	O
presented	O
at	O
the	O
Microsoft	O
CD-ROM	B-Device
Conference	O
in	O
March	O
1986	O
.	O
</s>
<s>
CD-ROMs	B-Device
began	O
being	O
used	O
in	O
home	B-Device
video	I-Device
game	I-Device
consoles	I-Device
starting	O
with	O
the	O
PC	O
Engine	O
CD-ROM²	O
(	O
TurboGrafx-CD	O
)	O
in	O
1988	O
,	O
while	O
CD-ROM	B-Device
drives	O
had	O
also	O
become	O
available	O
for	O
home	O
computers	O
by	O
the	O
end	O
of	O
the	O
1980s	O
.	O
</s>
<s>
In	O
1990	O
,	O
Data	B-General_Concept
East	O
demonstrated	O
an	O
arcade	O
system	O
board	O
that	O
supported	O
CD-ROMs	B-Device
,	O
similar	O
to	O
1980s	O
laserdisc	O
video	O
games	O
but	O
with	O
digital	O
data	B-General_Concept
,	O
allowing	O
more	O
flexibility	O
than	O
older	O
laserdisc	O
games	O
.	O
</s>
<s>
By	O
early	O
1990	O
,	O
about	O
300,000	O
CD-ROM	B-Device
drives	O
were	O
sold	O
in	O
Japan	O
,	O
while	O
125,000	O
CD-ROM	B-Device
discs	O
were	O
being	O
produced	O
monthly	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Some	O
computers	O
which	O
were	O
marketed	O
in	O
the	O
1990s	O
were	O
called	O
"	O
multimedia	O
"	O
computers	O
because	O
they	O
incorporated	O
a	O
CD-ROM	B-Device
drive	O
,	O
which	O
allowed	O
for	O
the	O
delivery	O
of	O
several	O
hundred	O
megabytes	O
of	O
video	O
,	O
picture	O
,	O
and	O
audio	O
data	B-General_Concept
.	O
</s>
<s>
CD-ROMs	B-Device
are	O
identical	O
in	O
appearance	O
to	O
audio	O
CDs	O
,	O
and	O
data	B-General_Concept
are	O
stored	O
and	O
retrieved	O
in	O
a	O
very	O
similar	O
manner	O
(	O
only	O
differing	O
from	O
audio	O
CDs	O
in	O
the	O
standards	O
used	O
to	O
store	O
the	O
data	B-General_Concept
)	O
.	O
</s>
<s>
The	O
most	O
common	O
size	O
of	O
CD-ROM	B-Device
is	O
120mm	O
in	O
diameter	O
,	O
though	O
the	O
smaller	O
Mini	O
CD	O
standard	O
with	O
an	O
80mm	O
diameter	O
,	O
as	O
well	O
as	O
shaped	O
compact	O
discs	O
in	O
numerous	O
non-standard	O
sizes	O
and	O
molds	O
(	O
e.g.	O
,	O
business	O
card-sized	O
media	O
)	O
,	O
also	O
exist	O
.	O
</s>
<s>
Data	B-General_Concept
is	O
stored	O
on	O
the	O
disc	O
as	O
a	O
series	O
of	O
microscopic	O
indentations	O
called	O
"	O
pits	O
"	O
,	O
with	O
the	O
non-indented	O
spaces	O
between	O
them	O
called	O
"	O
lands	O
"	O
.	O
</s>
<s>
This	O
is	O
converted	O
into	O
binary	O
data	B-General_Concept
.	O
</s>
<s>
Several	O
formats	O
are	O
used	O
for	O
data	B-General_Concept
stored	O
on	O
compact	O
discs	O
,	O
known	O
as	O
the	O
Rainbow	O
Books	O
.	O
</s>
<s>
The	O
Yellow	B-Device
Book	I-Device
,	O
created	O
in	O
1983	O
,	O
defines	O
the	O
specifications	O
for	O
CD-ROMs	B-Device
,	O
standardized	O
in	O
1988	O
as	O
the	O
ISO/IEC	B-Device
10149	I-Device
standard	O
and	O
in	O
1989	O
as	O
the	O
ECMA-130	B-Device
standard	O
.	O
</s>
<s>
The	O
CD-ROM	B-Device
standard	O
builds	O
on	O
top	O
of	O
the	O
original	O
Red	O
Book	O
CD-DA	O
standard	O
for	O
CD	O
audio	O
.	O
</s>
<s>
Other	O
standards	O
,	O
such	O
as	O
the	O
White	O
Book	O
for	O
Video	O
CDs	O
,	O
further	O
define	O
formats	O
based	O
on	O
the	O
CD-ROM	B-Device
specifications	O
.	O
</s>
<s>
The	O
Yellow	B-Device
Book	I-Device
itself	O
is	O
not	O
freely	O
available	O
,	O
but	O
the	O
standards	O
with	O
the	O
corresponding	O
content	O
can	O
be	O
downloaded	O
for	O
free	O
from	O
ISO	B-General_Concept
or	O
ECMA	O
.	O
</s>
<s>
There	O
are	O
several	O
standards	O
that	O
define	O
how	O
to	O
structure	O
data	B-General_Concept
files	O
on	O
a	O
CD-ROM	B-Device
.	O
</s>
<s>
ISO	B-Application
9660	I-Application
defines	O
the	O
standard	O
file	B-Application
system	I-Application
for	O
a	O
CD-ROM	B-Device
.	O
</s>
<s>
ISO	B-General_Concept
13490	O
is	O
an	O
improvement	O
on	O
this	O
standard	O
which	O
adds	O
support	O
for	O
non-sequential	O
write-once	B-Device
and	O
re-writeable	O
discs	O
such	O
as	O
CD-R	O
and	O
CD-RW	O
,	O
as	O
well	O
as	O
multiple	O
sessions	O
.	O
</s>
<s>
The	O
ISO	B-General_Concept
13346	O
standard	O
was	O
designed	O
to	O
address	O
most	O
of	O
the	O
shortcomings	O
of	O
ISO	B-Application
9660	I-Application
,	O
and	O
a	O
subset	O
of	O
it	O
evolved	O
into	O
the	O
UDF	O
format	O
,	O
which	O
was	O
adopted	O
for	O
DVDs	O
.	O
</s>
<s>
A	O
bootable	O
CD	O
specification	O
,	O
called	O
El	B-Device
Torito	I-Device
,	O
was	O
issued	O
in	O
January	O
1995	O
,	O
to	O
make	O
a	O
CD	O
emulate	O
a	O
hard	B-Device
disk	I-Device
or	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Pre-pressed	O
CD-ROMs	B-Device
are	O
mass-produced	O
by	O
a	O
process	O
of	O
stamping	O
where	O
a	O
glass	O
master	O
disc	O
is	O
created	O
and	O
used	O
to	O
make	O
"	O
stampers	O
"	O
,	O
which	O
are	O
in	O
turn	O
used	O
to	O
manufacture	O
multiple	O
copies	O
of	O
the	O
final	O
disc	O
with	O
the	O
pits	O
already	O
present	O
.	O
</s>
<s>
Recordable	O
(	O
CD-R	O
)	O
and	O
rewritable	O
(	O
CD-RW	O
)	O
discs	O
are	O
manufactured	O
by	O
a	O
different	O
method	O
,	O
whereby	O
the	O
data	B-General_Concept
are	O
recorded	O
on	O
them	O
by	O
a	O
laser	O
changing	O
the	O
properties	O
of	O
a	O
dye	O
or	O
phase	O
transition	O
material	O
in	O
a	O
process	O
that	O
is	O
often	O
referred	O
to	O
as	O
"	O
burning	B-Application
"	O
.	O
</s>
<s>
Data	B-General_Concept
stored	O
on	O
CD-ROMs	B-Device
follows	O
the	O
standard	O
CD	O
data	B-General_Concept
encoding	O
techniques	O
described	O
in	O
the	O
Red	O
Book	O
specification	O
(	O
originally	O
defined	O
for	O
audio	O
CD	O
only	O
)	O
.	O
</s>
<s>
This	O
includes	O
cross-interleaved	B-Error_Name
Reed	I-Error_Name
–	I-Error_Name
Solomon	I-Error_Name
coding	I-Error_Name
(	O
CIRC	B-Error_Name
)	O
,	O
eight-to-fourteen	B-Protocol
modulation	I-Protocol
(	O
EFM	O
)	O
,	O
and	O
the	O
use	O
of	O
pits	O
and	O
lands	O
for	O
coding	O
the	O
bits	O
into	O
the	O
physical	O
surface	O
of	O
the	O
CD	O
.	O
</s>
<s>
The	O
structures	O
used	O
to	O
group	O
data	B-General_Concept
on	O
a	O
CD-ROM	B-Device
are	O
also	O
derived	O
from	O
the	O
Red	O
Book	O
.	O
</s>
<s>
Like	O
audio	O
CDs	O
(	O
CD-DA	O
)	O
,	O
a	O
CD-ROM	B-Device
sector	B-Application
contains	O
2,352	O
bytes	B-Application
of	O
user	O
data	B-General_Concept
,	O
composed	O
of	O
98	O
frames	O
,	O
each	O
consisting	O
of	O
33	O
bytes	B-Application
(	O
24	O
bytes	B-Application
for	O
the	O
user	O
data	B-General_Concept
,	O
8	O
bytes	B-Application
for	O
error	B-Error_Name
correction	I-Error_Name
,	O
and	O
1	O
byte	B-Application
for	O
the	O
subcode	O
)	O
.	O
</s>
<s>
Unlike	O
audio	O
CDs	O
,	O
the	O
data	B-General_Concept
stored	O
in	O
these	O
sectors	O
corresponds	O
to	O
any	O
type	O
of	O
digital	O
data	B-General_Concept
,	O
not	O
audio	O
samples	O
encoded	O
according	O
to	O
the	O
audio	O
CD	O
specification	O
.	O
</s>
<s>
To	O
structure	O
,	O
address	O
and	O
protect	O
this	O
data	B-General_Concept
,	O
the	O
CD-ROM	B-Device
standard	O
further	O
defines	O
two	O
sector	B-Application
modes	O
,	O
Mode	O
1	O
and	O
Mode	O
2	O
,	O
which	O
describe	O
two	O
different	O
layouts	O
for	O
the	O
data	B-General_Concept
inside	O
a	O
sector	B-Application
.	O
</s>
<s>
A	O
track	O
(	O
a	O
group	O
of	O
sectors	O
)	O
inside	O
a	O
CD-ROM	B-Device
only	O
contains	O
sectors	O
in	O
the	O
same	O
mode	O
,	O
but	O
if	O
multiple	O
tracks	O
are	O
present	O
in	O
a	O
CD-ROM	B-Device
,	O
each	O
track	O
can	O
have	O
its	O
sectors	O
in	O
a	O
different	O
mode	O
from	O
the	O
rest	O
of	O
the	O
tracks	O
.	O
</s>
<s>
Both	O
Mode	O
1	O
and	O
2	O
sectors	O
use	O
the	O
first	O
16	O
bytes	B-Application
for	O
header	B-General_Concept
information	O
,	O
but	O
differ	O
in	O
the	O
remaining	O
2,336	O
bytes	B-Application
due	O
to	O
the	O
use	O
of	O
error	B-Error_Name
correction	I-Error_Name
bytes	B-Application
.	O
</s>
<s>
Unlike	O
an	O
audio	O
CD	O
,	O
a	O
CD-ROM	B-Device
cannot	O
rely	O
on	O
error	O
concealment	O
by	O
interpolation	B-Algorithm
;	O
a	O
higher	O
reliability	O
of	O
the	O
retrieved	O
data	B-General_Concept
is	O
required	O
.	O
</s>
<s>
To	O
achieve	O
improved	O
error	B-Error_Name
correction	I-Error_Name
and	I-Error_Name
detection	I-Error_Name
,	O
Mode	O
1	O
,	O
used	O
mostly	O
for	O
digital	O
data	B-General_Concept
,	O
adds	O
a	O
32-bit	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
code	O
for	O
error	B-Error_Name
detection	I-Error_Name
,	O
and	O
a	O
third	O
layer	O
of	O
Reed	B-Error_Name
–	I-Error_Name
Solomon	I-Error_Name
error	I-Error_Name
correction	I-Error_Name
using	O
a	O
Reed-Solomon	B-Error_Name
Product-like	O
Code	O
(	O
RSPC	O
)	O
.	O
</s>
<s>
Mode	O
1	O
therefore	O
contains	O
288	O
bytes	B-Application
per	O
sector	B-Application
for	O
error	B-Error_Name
detection	I-Error_Name
and	I-Error_Name
correction	I-Error_Name
,	O
leaving	O
2,048	O
bytes	B-Application
per	O
sector	B-Application
available	O
for	O
data	B-General_Concept
.	O
</s>
<s>
Mode	O
2	O
,	O
which	O
is	O
more	O
appropriate	O
for	O
image	O
or	O
video	O
data	B-General_Concept
(	O
where	O
perfect	O
reliability	O
may	O
be	O
a	O
little	O
bit	O
less	O
important	O
)	O
,	O
contains	O
no	O
additional	O
error	B-Error_Name
detection	I-Error_Name
or	O
correction	O
bytes	B-Application
,	O
having	O
therefore	O
2,336	O
available	O
data	B-General_Concept
bytes	B-Application
per	O
sector	B-Application
.	O
</s>
<s>
Note	O
that	O
both	O
modes	O
,	O
like	O
audio	O
CDs	O
,	O
still	O
benefit	O
from	O
the	O
lower	O
layers	O
of	O
error	B-Error_Name
correction	I-Error_Name
at	O
the	O
frame	O
level	O
.	O
</s>
<s>
Before	O
being	O
stored	O
on	O
a	O
disc	O
with	O
the	O
techniques	O
described	O
above	O
,	O
each	O
CD-ROM	B-Device
sector	B-Application
is	O
scrambled	O
to	O
prevent	O
some	O
problematic	O
patterns	O
from	O
showing	O
up	O
.	O
</s>
<s>
The	O
following	O
table	O
shows	O
a	O
comparison	O
of	O
the	O
structure	O
of	O
sectors	O
in	O
CD-DA	O
and	O
CD-ROMs	B-Device
:	O
</s>
<s>
The	O
net	O
byte	B-Application
rate	O
of	O
a	O
Mode-1	O
CD-ROM	B-Device
,	O
based	O
on	O
comparison	O
to	O
CD-DA	O
audio	O
standards	O
,	O
is	O
44,100	O
Hz	O
×	O
16	O
bits/sample	O
×	O
2	O
channels	O
×	O
2,048	O
/	O
2,352	O
/	O
8	O
=	O
150	O
KB/s	O
(	O
150	O
×	O
210	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
for	O
Mode	O
1	O
CD-ROMs	B-Device
,	O
a	O
1×	O
CD-ROM	B-Device
drive	O
reads	O
150/2	O
=	O
75	O
consecutive	O
sectors	O
per	O
second	O
.	O
</s>
<s>
The	O
playing	O
time	O
of	O
a	O
standard	O
CD	O
is	O
74	B-Device
minutes	I-Device
,	O
or	O
4,440	O
seconds	O
,	O
contained	O
in	O
333,000	O
blocks	O
or	O
sectors	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
net	O
capacity	O
of	O
a	O
Mode-1	O
CD-ROM	B-Device
is	O
650	O
MB	O
(	O
650	O
×	O
220	O
)	O
.	O
</s>
<s>
CD-ROM	B-Device
XA	O
is	O
an	O
extension	O
of	O
the	O
Yellow	B-Device
Book	I-Device
standard	O
for	O
CD-ROMs	B-Device
that	O
combines	O
compressed	O
audio	O
,	O
video	O
and	O
computer	O
data	B-General_Concept
,	O
allowing	O
all	O
to	O
be	O
accessed	O
simultaneously	O
.	O
</s>
<s>
It	O
was	O
intended	O
as	O
a	O
bridge	O
between	O
CD-ROM	B-Device
and	O
CD-i	B-Device
(	O
Green	B-Device
Book	I-Device
)	O
and	O
was	O
published	O
by	O
Sony	O
and	O
Philips	O
,	O
and	O
backed	O
by	O
Microsoft	O
,	O
in	O
1991	O
,	O
first	O
announced	O
in	O
September	O
1988	O
.	O
</s>
<s>
CD-ROM	B-Device
XA	O
defines	O
two	O
new	O
sector	B-Application
layouts	O
,	O
called	O
Mode	O
2	O
Form	O
1	O
and	O
Mode	O
2	O
Form	O
2	O
(	O
which	O
are	O
different	O
from	O
the	O
original	O
Mode	O
2	O
)	O
.	O
</s>
<s>
XA	O
Mode	O
2	O
Form	O
1	O
is	O
similar	O
to	O
the	O
Mode	O
1	O
structure	O
described	O
above	O
,	O
and	O
can	O
interleave	O
with	O
XA	O
Mode	O
2	O
Form	O
2	O
sectors	O
;	O
it	O
is	O
used	O
for	O
data	B-General_Concept
.	O
</s>
<s>
XA	O
Mode	O
2	O
Form	O
2	O
has	O
2,324	O
bytes	B-Application
of	O
user	O
data	B-General_Concept
,	O
and	O
is	O
similar	O
to	O
the	O
standard	O
Mode	O
2	O
but	O
with	O
error	B-Error_Name
detection	I-Error_Name
bytes	B-Application
added	O
(	O
though	O
no	O
error	B-Error_Name
correction	I-Error_Name
)	O
.	O
</s>
<s>
It	O
can	O
interleave	O
with	O
XA	O
Mode	O
2	O
Form	O
1	O
sectors	O
,	O
and	O
it	O
is	O
used	O
for	O
audio/video	O
data	B-General_Concept
.	O
</s>
<s>
Video	O
CDs	O
,	O
Super	O
Video	O
CDs	O
,	O
Photo	O
CDs	O
,	O
Enhanced	B-Application
Music	I-Application
CDs	I-Application
and	O
CD-i	B-Device
use	O
these	O
sector	B-Application
modes	O
.	O
</s>
<s>
The	O
following	O
table	O
shows	O
a	O
comparison	O
of	O
the	O
structure	O
of	O
sectors	O
in	O
CD-ROM	B-Device
XA	O
modes	O
:	O
</s>
<s>
When	O
a	O
disc	B-Application
image	I-Application
of	O
a	O
CD-ROM	B-Device
is	O
created	O
,	O
this	O
can	O
be	O
done	O
in	O
either	O
"	O
raw	O
"	O
mode	O
(	O
extracting	O
2,352	O
bytes	B-Application
per	O
sector	B-Application
,	O
independent	O
of	O
the	O
internal	O
structure	O
)	O
,	O
or	O
obtaining	O
only	O
the	O
sector	B-Application
's	O
useful	O
data	B-General_Concept
(	O
2,048	O
/2	O
,	O
336/2	O
,	O
352/2	O
,	O
324	O
bytes	B-Application
depending	O
on	O
the	O
CD-ROM	B-Device
mode	O
)	O
.	O
</s>
<s>
The	O
file	O
size	O
of	O
a	O
disc	B-Application
image	I-Application
created	O
in	O
raw	O
mode	O
is	O
always	O
a	O
multiple	O
of	O
2,352	O
bytes	B-Application
(	O
the	O
size	O
of	O
a	O
block	O
)	O
.	O
</s>
<s>
Disc	B-Application
image	I-Application
formats	O
that	O
store	O
raw	O
CD-ROM	B-Device
sectors	O
include	O
CCD/IMG	O
,	O
CUE/BIN	O
,	O
and	O
MDS/MDF	B-General_Concept
.	O
</s>
<s>
The	O
size	O
of	O
a	O
disc	B-Application
image	I-Application
created	O
from	O
the	O
data	B-General_Concept
in	O
the	O
sectors	O
will	O
depend	O
on	O
the	O
type	O
of	O
sectors	O
it	O
is	O
using	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
CD-ROM	B-Device
mode	O
1	O
image	O
is	O
created	O
by	O
extracting	O
only	O
each	O
sector	B-Application
's	O
data	B-General_Concept
,	O
its	O
size	O
will	O
be	O
a	O
multiple	O
of	O
2,048	O
;	O
this	O
is	O
usually	O
the	O
case	O
for	O
ISO	B-General_Concept
disc	I-General_Concept
images	I-General_Concept
.	O
</s>
<s>
On	O
a	O
74-minute	O
CD-R	O
,	O
it	O
is	O
possible	O
to	O
fit	O
larger	O
disc	B-Application
images	I-Application
using	O
raw	O
mode	O
,	O
up	O
to	O
333,000	O
×	O
2,352	O
=	O
783,216,000	O
bytes	B-Application
(	O
~	O
747	O
MB	O
)	O
.	O
</s>
<s>
The	O
14.8	O
%	O
increase	O
is	O
due	O
to	O
the	O
discarding	O
of	O
error	B-Error_Name
correction	I-Error_Name
data	B-General_Concept
.	O
</s>
<s>
CD-ROM	B-Device
capacities	O
are	O
normally	O
expressed	O
with	O
binary	O
prefixes	O
,	O
subtracting	O
the	O
space	O
used	O
for	O
error	B-Error_Name
correction	I-Error_Name
data	B-General_Concept
.	O
</s>
<s>
The	O
capacity	O
of	O
a	O
CD-ROM	B-Device
depends	O
on	O
how	O
close	O
the	O
outward	O
data	B-General_Concept
track	O
is	O
extended	O
to	O
the	O
disc	O
's	O
outer	O
rim	O
.	O
</s>
<s>
A	O
standard	O
120mm	O
,	O
700	O
MB	O
CD-ROM	B-Device
can	O
actually	O
hold	O
about	O
703	O
MB	O
of	O
data	B-General_Concept
with	O
error	B-Error_Name
correction	I-Error_Name
(	O
or	O
847	O
MB	O
total	O
)	O
.	O
</s>
<s>
In	O
comparison	O
,	O
a	O
single-layer	O
DVD-ROM	O
can	O
hold	O
4.7	O
GB	O
(	O
4.7	O
×	O
109	O
bytes	B-Application
)	O
of	O
error-protected	O
data	B-General_Concept
,	O
more	O
than	O
6	O
CD-ROMs	B-Device
.	O
</s>
<s>
+	O
Capacities	O
of	O
Compact	O
Disc	O
types	O
(	O
90	O
and	O
99	O
minute	O
discs	O
are	O
not	O
standard	O
)	O
Type	O
Sectors	O
Data	B-General_Concept
(	O
mode	O
1	O
)	O
max	O
.	O
</s>
<s>
CD-ROM	B-Device
discs	O
are	O
read	O
using	O
CD-ROM	B-Device
drives	O
.	O
</s>
<s>
A	O
CD-ROM	B-Device
drive	O
may	O
be	O
connected	O
to	O
the	O
computer	O
via	O
an	O
IDE	O
(	O
ATA	B-Protocol
)	O
,	O
SCSI	B-Architecture
,	O
SATA	O
,	O
FireWire	B-Protocol
,	O
or	O
USB	B-Protocol
interface	O
or	O
a	O
proprietary	O
interface	O
,	O
such	O
as	O
the	O
Panasonic	O
CD	O
interface	O
,	O
LMSI/Philips	O
,	O
Sony	O
and	O
Mitsumi	O
standards	O
.	O
</s>
<s>
Virtually	O
all	O
modern	O
CD-ROM	B-Device
drives	O
can	O
also	O
play	O
audio	O
CDs	O
(	O
as	O
well	O
as	O
Video	O
CDs	O
and	O
other	O
data	B-General_Concept
standards	O
)	O
when	O
used	O
with	O
the	O
right	O
software	O
.	O
</s>
<s>
CD-ROM	B-Device
drives	O
employ	O
a	O
near-infrared	O
780	O
nm	O
laser	O
diode	O
.	O
</s>
<s>
CD-ROM	B-Device
drives	O
are	O
rated	O
with	O
a	O
speed	O
factor	O
relative	O
to	O
music	O
CDs	O
.	O
</s>
<s>
If	O
a	O
CD-ROM	B-Device
is	O
read	O
at	O
the	O
same	O
rotational	O
speed	O
as	O
an	O
audio	O
CD	O
,	O
the	O
data	B-General_Concept
transfer	O
rate	O
is	O
150	O
Kbyte/s	O
,	O
commonly	O
called	O
"	O
1×	O
"	O
(	O
with	O
constant	B-Device
linear	I-Device
velocity	I-Device
,	O
short	O
"	O
CLV	O
"	O
)	O
.	O
</s>
<s>
At	O
this	O
data	B-General_Concept
rate	O
,	O
the	O
track	O
moves	O
along	O
under	O
the	O
laser	O
spot	O
at	O
about	O
1.2m/s	O
.	O
</s>
<s>
The	O
1×	O
speed	O
rating	O
for	O
CD-ROM	B-Device
(	O
150	O
Kbyte/s	O
)	O
is	O
different	O
from	O
the	O
1×	O
speed	O
rating	O
for	O
DVDs	O
(	O
1.32	O
MB/s	O
)	O
.	O
</s>
<s>
By	O
increasing	O
the	O
speed	O
at	O
which	O
the	O
disc	O
is	O
spun	O
,	O
data	B-General_Concept
can	O
be	O
transferred	O
at	O
greater	O
rates	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
CD-ROM	B-Device
drive	O
that	O
can	O
read	O
at	O
8×	O
speed	O
spins	O
the	O
disc	O
at	O
1600	O
to	O
4000	O
rpm	O
,	O
giving	O
a	O
linear	O
velocity	O
of	O
9.6m/s	O
and	O
a	O
transfer	O
rate	O
of	O
1200	O
Kbyte/s	O
.	O
</s>
<s>
Above	O
12×	O
speed	O
most	O
drives	O
read	O
at	O
Constant	B-Device
angular	I-Device
velocity	I-Device
(	O
CAV	B-Device
,	O
constant	O
rpm	O
)	O
so	O
that	O
the	O
motor	O
is	O
not	O
made	O
to	O
change	O
from	O
one	O
speed	O
to	O
another	O
as	O
the	O
head	O
seeks	O
from	O
place	O
to	O
place	O
on	O
the	O
disc	O
.	O
</s>
<s>
In	O
CAV	B-Device
mode	O
the	O
"	O
×	O
"	O
number	O
denotes	O
the	O
transfer	O
rate	O
at	O
the	O
outer	O
edge	O
of	O
the	O
disc	O
,	O
where	O
it	O
is	O
a	O
maximum	O
.	O
</s>
<s>
20×	O
was	O
thought	O
to	O
be	O
the	O
maximum	O
speed	O
due	O
to	O
mechanical	O
constraints	O
until	O
Samsung	B-Application
Electronics	O
introduced	O
the	O
SCR-3230	O
,	O
a	O
32×	O
CD-ROM	B-Device
drive	O
which	O
uses	O
a	O
ball	O
bearing	O
system	O
to	O
balance	O
the	O
spinning	O
disc	O
in	O
the	O
drive	O
to	O
reduce	O
vibration	O
and	O
noise	O
.	O
</s>
<s>
CAV	B-Device
drives	O
give	O
speeds	O
up	O
to	O
30×	O
at	O
the	O
outer	O
edge	O
of	O
the	O
disc	O
with	O
the	O
same	O
rotational	O
speed	O
as	O
a	O
standard	O
(	O
constant	B-Device
linear	I-Device
velocity	I-Device
,	O
CLV	O
)	O
12×	O
,	O
or	O
32×	O
with	O
a	O
slight	O
increase	O
.	O
</s>
<s>
However	O
,	O
due	O
to	O
the	O
nature	O
of	O
CAV	B-Device
(	O
linear	O
speed	O
at	O
the	O
inner	O
edge	O
is	O
still	O
only	O
12×	O
,	O
increasing	O
smoothly	O
in-between	O
)	O
the	O
actual	O
throughput	O
increase	O
is	O
less	O
than	O
30/12	O
;	O
in	O
fact	O
,	O
roughly	O
20×	O
average	O
for	O
a	O
completely	O
full	O
disc	O
,	O
and	O
even	O
less	O
for	O
a	O
partially	O
filled	O
one	O
.	O
</s>
<s>
Problems	O
with	O
vibration	O
,	O
owing	O
to	O
limits	O
on	O
achievable	O
symmetry	O
and	O
strength	O
in	O
mass-produced	O
media	O
,	O
mean	O
that	O
CD-ROM	B-Device
drive	O
speeds	O
have	O
not	O
massively	O
increased	O
since	O
the	O
late	O
1990s	O
.	O
</s>
<s>
Over	O
10	O
years	O
later	O
,	O
commonly	O
available	O
drives	O
vary	O
between	O
24×	O
(	O
slimline	O
and	O
portable	O
units	O
,	O
10×	O
spin	O
speed	O
)	O
and	O
52×	O
(	O
typically	O
CD	O
-	O
and	O
read-only	O
units	O
,	O
21×	O
spin	O
speed	O
)	O
,	O
all	O
using	O
CAV	B-Device
to	O
achieve	O
their	O
claimed	O
"	O
max	O
"	O
speeds	O
,	O
with	O
32×	O
through	O
48×	O
most	O
common	O
.	O
</s>
<s>
Even	O
so	O
,	O
these	O
speeds	O
can	O
cause	O
poor	O
reading	O
(	O
drive	O
error	B-Error_Name
correction	I-Error_Name
having	O
become	O
very	O
sophisticated	O
in	O
response	O
)	O
and	O
even	O
shattering	O
of	O
poorly	O
made	O
or	O
physically	O
damaged	O
media	O
,	O
with	O
small	O
cracks	O
rapidly	O
growing	O
into	O
catastrophic	O
breakages	O
when	O
centripetally	O
stressed	O
at	O
10,000	O
–	O
13,000	O
rpm	O
(	O
i.e.	O
</s>
<s>
40	O
–	O
52×	O
CAV	B-Device
)	O
.	O
</s>
<s>
Other	O
methods	O
of	O
improving	O
read	O
speed	O
were	O
trialled	O
such	O
as	O
using	O
multiple	O
optical	O
beams	O
,	O
increasing	O
throughput	O
up	O
to	O
72×	O
with	O
a	O
10×	O
spin	O
speed	O
,	O
but	O
along	O
with	O
other	O
technologies	O
like	O
90	O
~	O
99	O
minute	O
recordable	O
media	O
,	O
GigaRec	O
and	O
double-density	B-Device
compact	I-Device
disc	I-Device
(	O
Purple	B-Device
Book	I-Device
standard	O
)	O
recorders	O
,	O
their	O
utility	O
was	O
nullified	O
by	O
the	O
introduction	O
of	O
consumer	O
DVD-ROM	O
drives	O
capable	O
of	O
consistent	O
36×	O
equivalent	O
CD-ROM	B-Device
speeds	O
(	O
4×	O
DVD	O
)	O
or	O
higher	O
.	O
</s>
<s>
Additionally	O
,	O
with	O
a	O
700	O
MB	O
CD-ROM	B-Device
fully	O
readable	O
in	O
under	O
2½	O
minutes	O
at	O
52×	O
CAV	B-Device
,	O
increases	O
in	O
actual	O
data	B-General_Concept
transfer	O
rate	O
are	O
decreasingly	O
influential	O
on	O
overall	O
effective	O
drive	O
speed	O
when	O
taken	O
into	O
consideration	O
with	O
other	O
factors	O
such	O
as	O
loading/unloading	O
,	O
media	O
recognition	O
,	O
spin	O
up/down	O
and	O
random	O
seek	O
times	O
,	O
making	O
for	O
much	O
decreased	O
returns	O
on	O
development	O
investment	O
.	O
</s>
<s>
A	O
similar	O
stratification	O
effect	O
has	O
since	O
been	O
seen	O
in	O
DVD	O
development	O
where	O
maximum	O
speed	O
has	O
stabilised	O
at	O
16×	O
CAV	B-Device
(	O
with	O
exceptional	O
cases	O
between	O
18×	O
and	O
22×	O
)	O
and	O
capacity	O
at	O
4.3	O
and	O
8.5	O
GB	O
(	O
single	O
and	O
dual	O
layer	O
)	O
,	O
with	O
higher	O
speed	O
and	O
capacity	O
needs	O
instead	O
being	O
catered	O
to	O
by	O
Blu-ray	O
drives	O
.	O
</s>
<s>
CD-Recordable	O
drives	O
are	O
often	O
sold	O
with	O
three	O
different	O
speed	O
ratings	O
,	O
one	O
speed	O
for	O
write-once	B-Device
operations	O
,	O
one	O
for	O
re-write	O
operations	O
,	O
and	O
one	O
for	O
read-only	O
operations	O
.	O
</s>
<s>
Software	O
distributors	O
,	O
and	O
in	O
particular	O
distributors	O
of	O
computer	O
games	O
,	O
often	O
make	O
use	O
of	O
various	O
copy	O
protection	O
schemes	O
to	O
prevent	O
software	O
running	O
from	O
any	O
media	O
besides	O
the	O
original	O
CD-ROMs	B-Device
.	O
</s>
<s>
The	O
CD-ROM	B-Device
itself	O
may	O
contain	O
"	O
weak	O
"	O
sectors	O
to	O
make	O
copying	O
the	O
disc	O
more	O
difficult	O
,	O
and	O
additional	O
data	B-General_Concept
that	O
may	O
be	O
difficult	O
or	O
impossible	O
to	O
copy	O
to	O
a	O
CD-R	O
or	O
disc	B-Application
image	I-Application
,	O
but	O
which	O
the	O
software	O
checks	O
for	O
each	O
time	O
it	O
is	O
run	O
to	O
ensure	O
an	O
original	O
disc	O
and	O
not	O
an	O
unauthorized	O
copy	O
is	O
present	O
in	O
the	O
computer	O
's	O
CD-ROM	B-Device
drive	O
.	O
</s>
