CD and DVD technology

Soujit SenGupta

12.03.16

Brief History of Compact Digital Media

1980: The first Compact Disk player is produced by Sony/Phillips.

1982: The first Compact Disk is manufactured for sale, Billy Joel’s “52nd Street”

1984: First portable Compact Disk players enter the market followed by car CD players shortly after.

1985: Sony/Philips announce the standard for compact disc storage of computer data, the CD-ROM

1987: Video CD format is designed.

1991: CD-R (Compact Disk Recordable) technology is introduced as a new storage technology.

1996: Digital Versatile Disk(DVD) technology is introduced

1997: DVD’s and DVD players begin to enter the market

1998: DVD Recordable systems invented and begin to enter the market

2000: DVD movies become mainstream and replace analog VHS as the format of choice.

Compact Disk (CD) Basics

•Uses Digital Technology to store data in binary values of Zero and One

•Uses “Pits” and “Lands” to signify binary values

•CD’s Read at a Constant Linear Velocity (CLV)

•Capable of Storing Large Amounts of Data (up to 700MB)

•Uses Error Correction for reliable data retrieval even if the CD becomes lightly scratched.

Types Of Compact DisksCD Audio – The first type of CD that was available. This allows for

the storage of digital audio. These are playable in all current CD drives and car audio systems including DVD players.

CD-ROM – Computer Data is stored on these units such as games, applications, and other files. Only readable on computers.

CD-R – Allows users to write data once to a recordable Compact Disk. Can not be re-written and can be read in all current players

depending on wither the disk holds Audio or Data.

CD-RW – Users Can Write and Re-Write these special disks. However because of the disk format, they cannot be read in Audio CD

players or DVD players.

CD Basic Technology Principles

P r i n t e d L a b e l

P r o t e c t i v e L a c q u e r

A l u m i n u m L a y e r

P o l y c a r b o n a t e

This diagram shows the side view of a common CD.

Printed Label : The image on the top of the CD, more of a “secondary” protection device than anything else.Protective Lacquer: This protects the CD from scratches and helps reflect the CD player’s laser.Aluminum Layer: This is the reflective layer that primarily bounces the CD player’s laser back.Polycarbonate: Known industry wide as a very durable substance, Polycarbonate is a clear covering designed to protect the pits and lands in the CD surface.

A. A polycarbonate disc layer has the data encoded by using bumps.B. A shiny layer reflects the laser.C. A layer of lacquer protects the shiny layer.D. Artwork is screen printed on the top of the disc.E. A laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data

CD Audio: How Does It Work?Sound is Sampled at 40,000 Times per Second or Higher

Each Sample Must be Represented by at least a 16-bit number

Therefore, with 40,000 samples per second, and 16-bits per sample,that’s over 640,000 bits per second! Therefore a 1 minute long

music clip would take over 38,400,000 bits (+/- 38MB) for storage!

Computer CD-ROM’s

Divided Into Sectors Containing User Data and Error Correction Codes. Set up similar to hard drives however they do not have a “FAT” sector,

instead sectors are opened and closed with special pit and land combinations.

File Systems are used to store data for easy and quick access

CD Recordable BasicsP r i n t e d L a b e l

P r o t e c t i v e L a y e r

R e f l e c t i v e G o l d L a y e rD y e L a y e r

P o l y c a r b o n a t e

D a r k S p o t = P i tThis diagram shows the side view of a common CD.

Printed Label : The image on the top of the CD, more of a “secondary” protection device than anything else.Protective Lacquer: This protects the CD from scratches and helps reflect the CD player’s laser.Gold Layer: This is the reflective layer that primarily bounces the CD player’s laser back.Dye Layer: This is burned into Dark or Light spots by the CD Recorder drive. Imitates lands and pits.Polycarbonate: Known industry wide as a very durable substance, Polycarbonate is a clear covering designed to protect the pits and lands in the CD surface.

CD-R Technology

Can Only Write Data Once

Uses Gold Instead of Aluminum for its Reflective Layer, thus a higher cost than traditional CD’s

Uses Dye to “trick” the CD player Laser into thinking it is passing over real Pits and Lands, when in actuality it is merely passing

over light and dark spots in the dye.

CD-RW Technology

Allows Users to Write Many Times (However This is Limited)

Uses Alloy of Sliver, Indium, Antimony, and Tellurium for Reflective Layer

Uses varying power levels to read and write lands and pits.

High Power = Creates PitsMelts Alloy and Converts it to a High-reflectivity Crystalline state

Medium Power = Creates LandsMelts Alloy and Converts it to Natural Crystalline state

Low Power = For Reading…no change to CD surface.No Change in Alloy

Error Correction, Why Bother?

Error correction is an imperative part of CD technology, you cannot take good enough care of a CD to prevent errors. Sony and Phillips knew this, so they instituted the basics of Error Correction Technology.

Errors can be caused by:Manufacturing defects (Rare)Scratches (Very Common)

Error Correction Types:CIRC – (Cross Interleaved Read-Solomon Code) encoderEFM Modulation – (Eight to Fourteen)

CIRC Error Correction:

Can correct Error Bursts up to 3,500 bits long (2.4mm in length)

Helps to compensate for Error Bursts up to 12,000 bits (8.5mm). These types of errors are typically caused by minor scratches.

EFM Error Correction Technology

Works to ensure Pits and Land Lengths are no Less Than 3 channel bits and no More Than 11 Channel Bits

Very widely used in portable CD players because it helps to reduce the skipping effect of jitter and distortions.

The 14-bit words are chosen such that binary ones are always separated by a minimum of two and a maximum of ten binary zeroes. This is because bits are encoded with NRZI encoding, or modulo-2 integration, so that a binary one is stored on the disc as a change from a land to a pit or a pit to a land, while a binary zero is indicated by no change. A sequence 0011 would be changed into 1101 or its inverse 0010 depending on the previous pit written. If there are two zeroes between two consecutive ones, then the written sequence will have three consecutive zeros (or ones), for example, 010010 will translate into 100011 (or 011100). The EFM sequence 000100010010000100 will translate into 111000011100000111 (or its inverse).

DVD is Born!If CD is so great…why change it? Space limitations plagued CD’s to a life only in the music market, Video producers could not fit full length movies on a CD.

•The goal of DVD was to create a “vastly increased capacity, with the ability to feature an entire movie in high-quality digital video on a single side of a disc.”•They also wanted...Brighter colors, sharper pictures, and outstanding audio quality•The goal was a 4.7 gigabyte capacity with the ability to hold hours of full motion video and sound

Obviously they did it…but how?• DVD uses Smaller pit

and land dimensions, therefore the laser must me exponentially more accurate than with CD’s.

• More closely-spaced tracks, called "track pitch"

• A shorter-wavelength laser

The Wavelength Issue:

•DVD Players and DVD-ROM drives use a laser that emits high intensity red light at 650 and 635nm vs the

780 nanometers for CD technology

•These shorter wavelengths are better at reading the smaller, densely packed together pits and lands.

•The laser assembly has been re-engineered to produce a more tightly focused laser beam

How Many Layers Would You Like?

As an interesting consequence of using the new lasers and the new DVD design elements, they found that multiple sides and layers could be stacked onto a single DVD disk. A total of 4 configurations were found to be viable:

Single Side, Single Layer Single Side, Dual Layer

Double Side, Single Layer Double Side, Dual Layer

Single Side, Single Layer DVD

• Accounts for most DVD’s

• 4.7 GB of data capacity

• "7 times" the data capacity of today’s music CDs and CD-ROMs

Single Side, Dual Layer DVD

• 8.5 GB on one side

• additional 3.8 GB on the second layer

• more than "13 times" the capacity of today’s music CDs and CD-ROMs

Dual Side, Single Layer DVD

• 9.4 GB (4.7 on each side)

• provides a little more capacity

• Flipping the disc or having a DVD Player capable of two-sided playback is required

Dual Side, Dual Layer DVD

• Maximum capacity of 17GB (8.5GB on each side)

• Flipping the disc or having a DVD Player capable of two-sided playback is required

CD versus DVDGrudge Match of the Century!

Who has the advantage here?

Both discs are the same physical size (120 mm diameter & 1.2 mm thickness, which makes CDs compatible with DVD players. Both discs are made with the same basic technology and production processesBoth technologies read discs in the same mannerDVD software can be replicated from existing CD production facilities

However DVD has some tricks up its sleeves….

DVD can hold exponentially more data than a CD canDVD has Higher density data storage where smaller pits and smaller tracks in DVDs provide seven times storage alone compared to CDsDVD has less overhead & more area because the DVD’s error-correction scheme is more efficient and requires less storage space that can be used for other informationDVD can have Multi-layer storage whereas CD stores data on one layer on one side of disc. DVD can store up to two layers on up to two sides of the disc, which allows up to 4X the storage amount

Comparison

Specification CD DVDDisc Diameter 120 mm 120 mmDisc Thickness 1.2 mm 1.2 mmDisc Structure Single substrate Two bonded .6 mm substratesLaser Wavelength 780 nm (infrared) 635 or 650 nm (red)Numerical Aperture .45 .6Track Pitch 1600 nm 740 nmShortest Pit Length 830 nm 400 nmReference Speed 1.2 m/sec CLV 4.0 m/sec CLVData Layers 1 2Data Sides 1 2Data Capacity 650 MB 4.7 – 17.0 GBUser Data Rate 1.4 Mbps (Video-CD) 10.0 Mbps (DVD-Video)Readout Wavelength 780 nm 650 nmScanning Speed 1.2 – 1.4 m/s 3.49 – 3.84 m/sReflectivity 70% minimum 45 – 85%Modulation 8/14 8/16Error Correction CIRC RS-PCError Correction Overhead 23/34% 13%Format overhead 252% 136%

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