Presentation of CD-ROM - Compact Disc (CD) was invented by Sony
and Philips in 1981. In 1984, Compact Disc specifications have been extended
to enable it to store digital data. It’s called once-in CD-ROM. The engravers
have appeared later to the general public. Burn a CD allows you to enter data
above to read them later.
Geometry and composition of a CD (Compact Disc) is a disc
of 12 cm in diameter and 1.2 mm thick (the thickness varies from 1.1 to 1.5
mm) that can store digital information, that is to say, corresponding to 800
megabytes of data in binary language (0 or 1). A circular hole of 15 mm in
diameter in the middle of the CD allows for the center.
Composition of a CD:
The CD consists of three layers. The main layer is the thickest is
polycarbonate, a plastic resistant and transparent (1).
This plastic allows the light emitted by the laser when playing a CD. There is
then a reflective metallic coating (2) very often aluminum which will reflect
the light emitted by the laser. There is above all that a layer of protective
coating just protect the metal aggression Ultra Violets (3). Above all, there
is the printed surface used to dress the disc (4).
Principle of operation of playing a CD of this type, the
laser beam passes through the layer of polycarbonate and meets or not a
hollow. The beam is then reflected by the metallic coating. The passage of a
hollow lump or a bump to a low represents a 1 in binary language. The
remainder represents a 0. The laser light is then deflected heavily (we say it
is refracted), so that the dose of light returned by the reflective layer is
minimal. The reader understands when he is on January 1. The length of the
ground below, it is hump or hollow, given the length of the number of 0
located afterwards. The succession of 0 and 1 can then read the contents of
the disc. Note that unlike hard drives, a CD has only one runway organized
The curve is not regular but oscillate around its average curve (known as the
wobble). The frequency of these oscillations is to 22.05 KHz. This allows the
oscillation play head follow the curve and regulate the speed of rotation of
Modes of operation for reading CD reading speed constant linear
noted CLV: When a disc spins, speed tracks located in the center is less
important than the tracks located on the outside, so it is necessary to adapt
rotational speed of the disc depending on the position of the play head.
The reading speed of rotation constant angular noted CAV: it is to have a low
density of data on the periphery of the disk and a high density in the center
of the disk. In this way, the flows are the same in the centre and the
periphery of the disc. However, capacity is less.
Coding of physical information’s track consists of cells with a depth
of 0168 μ m, a width of 0.67 μ m long and variable. The tracks are physically
excluded them from a distance of about 1.6 μ m. The bottom of the cell is a
hollow spaces are flat.
This is the length of the cell that defines information. The size of a bit on
the CD is standardized and corresponds to the distance traveled by the light
beam to 231.4 nanoseconds, or 0,278 m μ the standard minimum speed of 1.2 m /
There must always be at least two bits with a value of 0 between two
consecutive bit to 1 and there can be no more than 10 bits with a value of
between 0 to 1 bits. That is why the length of a cell is at least as long as
needed to store the value OO1 (0,833 m μ) = 3T and the maximum length
corresponding to the value 00000000001 (3,054 m μ) = 11T.
A CD burner can be summed up in fact to do or not dimples on a CD. It is a
laser 10 times more powerful than a laser reading traditional written on the
CD. This corresponds to binary data (the passage of a hole in a lump or a bump
in a hole = 1 and the rest = 0).
The writing speed is identical to the reading speed CD-Rom, namely that 1X is
150KB / s.
Today, the CD’s most values burn to 72X. However, this speed is not reached on
the entire disc. At the beginning of the burning speed is lower, the more
advance and more it increases (this is due to the linear speed lowest in the
centre of the CD). Similarly, there is no need to go beyond 40 x burning
because the time saved is minimal compared to the risks of erasures of
Composition of a CR-R (Recordable Compact Disc)
When serious a CD is created on the CD this succession of alveoli. But it does
not physically distorts the record, there is a special layer
(2) compared to the normal CD. It is placed
between the polycarbonate and metal layer, it consists of an organic dye that
gives shade of the disk, usually green or blue. This dye is photosensitive,
meaning that its temperature will increase when it would submit a strong
light. When the laser reaches this layer, it burns locally to over 250
degrees. This gives the final burned areas and not burned. This reproduces the
succession of holes and bumps. During the reading, the passage of an area
burned in an area not burned, which puts more light corresponds to a 1 in
Composition of a CD-RW (Compact Disc Rewritable) A rewritable disc becomes
richer when two new layers. For the layer recordable
(3), using a mixture of silver, indium, antimony and tellurium.
By playing on the temperature of this alloy, we change its mechanical
properties. His condition is changing in two very specific temperatures: 200
degrees, it crystallizes and let the light. Beyond 600 °, it enters the
merger. The atoms then organized randomly. While the material is in this
state, if you do fall sharply its temperature below 200 degrees, the atoms do
not have time to reorganize crystal. There remain frozen. They say they are in
the amorphous phase. The light does more.
Depending on whether one wants to read, write or erase data on module power
laser. Thus, temperatures will be different. It reproduces succession of
transparent and opaque areas. Two dielectric layers (2)
(4) trap the mixture crystal (3). They
absorb the excess energy, protect the polycarbonate and metal layer too high
temperatures. During the erasure, it maintains locally layer recordable at a
temperature above the temperature of crystallization, then slowly drop the
temperature so that the atoms find their crystalline structure.
Monessen: This method creates a single session on the disc and does not
give the possibility to add data on the CD.
Multi-session: This method will burn a CD several times, creating a table of
contents (TOC for table of contents) 14Mo for each session. You can burn a 1
MB file, for example, and 1 month after burning a file of 200 MB data are not
Multivolume: That burning Multi-session which considers each session as a
Track At Once: This method will disable the laser between two tracks to create
a pause for 2 seconds between tracks on an audio CD.
Disc At Once: Unlike the previous method, the Disc At Once written on the CD
in a single trafficking. The tunes are chained.
Packet Writing: This method written on the CD packet.
Techniques gravure Burn Proof: BURN-Proof means Buffer Under RuN
Proof, which means to test Buffers Under runs. The Buffer Under runs are
errors that may occur during burning a CD, when the flow of data sent to the
burner is not sufficiently constant. This causes a vacuum of the
buffer-burner, and therefore a stranding burning.
The BURN-Proof technology allows us to avoid such incidents, which made the CD
the most often unusable. It can therefore also benefit the bottom of its games
during the burn, or any application greedy. If the flow of data is lacking,
the burning stops, then resumes when the tide is enough support.
The over burning: This technique is to exceed the capacity of blank media to
store some additional data. With it, you can, for example, burn 820 MB on a CD
with 800 MB But do not double the capacity of your blank CDs! a gain of 30 MB
is already enormous. To do this, we need your burning software and your
burner, support this technique.
Differentiating CD-ROM, differences between the burners are minimal and are
mostly in their color or their mark. It is still a few essential
Their interface (IDE or SCSI)
Their speed expressed as X (X equals 150 kb / s). A burner 40 / 12 / 48
serious CD-ROM at 40X, rewrites CDs at 12 X and reads CDs at 48X.
The access time in milliseconds. This is the time taken by the player to move
from one party to another CD.
Their integrated technologies (such as the Burn proof, for example). Do not
take a recorder that does not have this technology, which takes different
names depending on the manufacturer