CSIT 301 (Blum) 1

CD’s

CSIT 301 (Blum) 2

The medium has changed, but the geometry is the same (almost)

• CD-ROMs are random access devices. • CD, compact discs, are geometrically

similar to hard disks. • The difference is in the medium is which

the data is stored and how that data is accessed. – Where hard disks use magnetism, CDs use

light.

CSIT 301 (Blum) 3

Spiraling out of control

• Actually CDs are somewhat different geometrically. A CD consists of one continuous spiral rather than the concentric tracks that hard disks have.

• Nevertheless, one still talks of tracks and sectors. A CD sector contains 3234 bytes.

CSIT 301 (Blum) 4

CSIT 301 (Blum) 5

It’s done with mirrors

1. A laser provides a beam of light (infrared, not visible). The beam is bounced off of a mirror. The mirror serves as the “head”, the main moving part that directs the beam of light to the data of interest.

2. After bouncing off a mirror, the light passes through a lens which focuses it onto the designated region on the disk.

CSIT 301 (Blum) 6

Electromagnetic spectrum

IR (infrared) is light, we just can’t see it.

←Wavelength getting smaller

CSIT 301 (Blum) 7

Wavelengths getting smaller →

CSIT 301 (Blum) 8

Upon further reflection,

3. The light is then reflected from the CD surface. The amount of light that gets reflected depends upon whether or not the surface has a pit. The binary information, 1’s and 0’s, are encoded using pits which can be detected in the amount of light reflected.

4. The light is collected (more lenses and mirrors) and sent to a photo-detector.

CSIT 301 (Blum) 9

Light Voltage or Current

5. The photodetector takes a light signal and converts it into a voltage or current signal which is compatible with what the rest of the computer “understands.”

• Compared to floppies in which the heads are in contact with the medium and the hard disks in which they must be incredibly close, the CD “head” remains a fair distance from the medium.

• Furthermore, the photodetector does not have to move at all, just the lenses and mirrors.

CSIT 301 (Blum) 10

The pits

• The CD starts off flat and then the data is written by creating the pits. – Parts of the disc that are not pitted are called “lands.”

• The lands reflect light cleanly while the pits diffuse (spread out the light).

• Thus there is a difference in the amount of light collected when the laser reflects from a land versus when it reflects from a pit.

CSIT 301 (Blum) 11

The same but different

• A conventional CD-ROM drive is like the hard-drive in that a spindle motor rotates the disk and the “head” is positioned radially. So data is located by finding the correct radius and waiting for the right angle (sector) to swing around. The CD even has servo information like the hard drive.

• What is different is that the hard disk rotates at a constant angular velocity, CAV, while the CD rotates at a constant linear velocity, CLV, (and thus a variable angular speed).

CSIT 301 (Blum) 12

Keeping the beat• Recall that with hard drives either we wasted storage

capacity (density) at the larger radii or we used zoned-bit recording to store more data there. Modern hard drives opt for the latter and thus have uneven data access rates. Data is accessed more quickly at the larger radii since more data is stored there.

• The CD technology grew out of the music industry, and there a constant data rate was important. When the head is positioned at smaller radii, the disk spins faster to ensure a constant data rate.

CSIT 301 (Blum) 13

Speed• A standard audio CD spins from anywhere

between 210 to 539 revolutions per minute (RPM) – depending on the head’s radial position.

• There was not much motivation to change this speed for audio CDs but when CDs started to be used for data storage, there was.

• The speeds were increased in multiplicative factors of the standard audio CD speed (2X, 3X, 4X, etc.

CSIT 301 (Blum) 14

CLV CAV

• As speeds increased for data reading, the technology switched from constant linear velocity to constant angular velocity. – It is too difficult to vary the speed when it is spinning

so quickly. • Halving your speed when you’re going at 10 mph is one thing,

halving your speed when you’re going 100 mph is another thing entirely

– The speeds are still reported as multiplicative factors of the standard audio CD speed.

CSIT 301 (Blum) 15

CD Speed

CSIT 301 (Blum) 16

CLV vs. CAV

CSIT 301 (Blum) 17

CD

• An audio CD holds about 783 MB of data. • Basically a CD is a piece of plastic. • The plastic has small pits (or bumps)

organized in a long spiral. • The plastic is sprayed (sputtered) with

aluminum to provide a reflective surface. • Then the aluminum surface is covered with

more plastic for protection. (the label side).

CSIT 301 (Blum) 18

What is a pit when viewed from the label side is a bump viewed form the other side, which is what is actually done.

The data is read through the bottom but is stored closer to the top.

CSIT 301 (Blum) 19

Writing

• CDs which the user can write to are made differently.

• A CD which can be written by the user once is called CD-R. The “R” is for “recordable.” A.k.a. “write once.”

• A CD which can be written many times by the user is called CD-RW. The “RW” is for “rewritable.”

CSIT 301 (Blum) 20

Sizes• A track is about half micron (millionth of a meter)

wide. • There is 1.6 microns between tracks. • A pit/bump is 0.5 microns wide (the width of the

track), as short as 0.83 microns long and 125 nanometers high.– The length varies depending on the data. – A nanometer is a billionth of a meter.

• The spiral would be 3.5 miles if it were stretched out (unrolled).

CSIT 301 (Blum) 21

CD Drive Parts

CSIT 301 (Blum) 22

Connectors and Jumpers

• CD-ROM connectors and jumpers are fairly standardized. – A four-pin power connector. – 40-pin data connector for IDE/ATAPI or 50-pin

connector for SCSI. – Jumpers (different for ATAPI and SCSI)– Audio connector: 3- or 4-wire connector goes

to the sound card so one can play audio CDs.

CSIT 301 (Blum) 23

CD Drive Form Factor

• CD-ROM drives fit into a standard half-height bay (5.25 inches wide and 1.75 inches high).

• Tray-loading CD-ROM drives, the standard kind, must be mounted horizontally.

• Caddy-based drives can be mounted vertically but typically are mounted horizontally.

CSIT 301 (Blum) 24

CD Formats

• Basically, all CDs are the same, pits and lands are used to store binary information. However, CDs have different formats, i.e. different ways of organizing and encoding the information.

• A CD’s format is somewhat like the idea of the file system of a hard disk.

• A given CD drive may not understand all of the formats.

CSIT 301 (Blum) 25

Coloring Books

• When one is discussing the specifications of various CD formats, one talks about the color of the book.

• For example, the specifications for standard audio CDs (CD-DA, digital audio) are kept in the red book.

• The specs for CD-ROM EA (extended architecture) are in the yellow book.

CSIT 301 (Blum) 26

CD-DA

• The first CDs were audio CDs. • The standards for this format were set in 1980 by

Philips and Sony. They constitute the “red book.”• Since this was the first set of standards, it includes

both the physical standard as well as the logical standards.

• The physical standards include the size and shape of the disk as well as how the data is read.

CSIT 301 (Blum) 27

Digitizing

• Consider for example an analog voltage signal. It can be continuous in two senses: 1. the voltage varies continuously in time

2. At a given instance, the voltage can take on any value from a continuum

• To digitize the signal, the time continuum and the voltage continuum have to be converted into discrete sets of values.

CSIT 301 (Blum) 28

Analogy: Digitizing an image

Discretize spaceDiscretize color

CSIT 301 (Blum) 29

Sampling

• Breaking up the time continuum is known as “sampling.”

• Motion pictures are an example of sampling: a rapid succession of snapshots (still pictures) are taken, if the sampling frequency (the number of pictures (frames) per second) is sufficiently high, the brain perceives the playback as continuous motion.

• Muybridge demo

CSIT 301 (Blum) 30

(pseudo)-Analog wave

-1.5

-1

-0.5

0

0.5

1

1.5

Continuous in time

Con

tin

uou

s va

lues

CSIT 301 (Blum) 31

Sampled Wave

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 32

One of Nyquist’s Theorems

• Signals can be thought of as being comprised of sine waves of various frequencies (Fourier).– Demo

• Nyquist says that to accurately represent a signal, one’s sampling frequency must be at least double its highest constituent frequency. – For example, in the phone system the choice was made

to sample at a frequency of 8000 Hz.

CSIT 301 (Blum) 33

Nyquist Sampling Example• In the following sequence of graphs, a sine wave

is sampled. • The frequency of the sine wave is doubled each

time, while the sampling frequency is kept fixed.– Case E does not resemble a sine wave but alternates up

and down with the correct frequency– Case F oscillates very quickly (alternating up and

down), but its amplitude seems to vary at a much lower frequency. This was not a feature of the actual wave being sampled.

– Case G only has the slowly varying feature when the actual wave sampled varying quite rapidly.

CSIT 301 (Blum) 34

A: sf=10, f=0.159sf: sampling freq. F: freq.

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 35

B : sf=10, f=0.318

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 36

C : sf=10, f=0.637

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 37

D : sf=10, f=1.273

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 38

E : sf=10, f=2.546

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 39

F : sf=10, f=5.093

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 40

G : sf=10, f=10.186

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 41

The other half of the problem

• At the instance one is sampling, the signal can still take on an infinite number of values.

• Digitizing requires one to choose a discrete set of allowed values. – For example, to digitize an image one can choose two

values (black and white) or allow for shades of gray or allow for combinations of red, blue and green, etc.

• For example, in the phone system, it was decided that 256 values would be allowed. – 256 values can be represented by 8 bits.

CSIT 301 (Blum) 42

Sine: 5 values

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 43

Sine: 9 values

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 44

Sine: 17 values

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 45

Sine: 33 values

-1.5

-1

-0.5

0

0.5

1

1.5

CSIT 301 (Blum) 46

CD-DA Sampling• The phone system uses a sampling frequency of

8000 Hz and uses 1 byte (256 levels) to represent the possible values of each sample.

• A higher quality sound is expected from CDs, the red book specifies a sampling frequency of 44,100 Hz and use 2 bytes of data (65536 levels) to represent the possible levels of each sample. And the sampling is done in stereo.

• This corresponds to 176,400 bytes /second. 176,400 = 44,100 2 2

CSIT 301 (Blum) 47

Human-based sampling rate

• Humans hear sound in the range 20 to 20,000 Hz. 

• Double the highest frequency (a la Nyquist) giving 40,000 (the actual number used is 44,100).

• Use two bytes per sample. • Record in stereo.• Result: 44,100 2 2 = 176400 bytes/sec.

CSIT 301 (Blum) 48

CD-DA (Cont.)• In CD-DA, the disk is broken into blocks or

sectors.

• A sector has 3234 bytes. In CD-DA, 2352 of those bytes are actual data. The rest is – Data for timing and location (the CD analog of

the hard disk’s servo information) – 98 bytes – Error-Correction-Code (ECC) and Error

Detection Code (EDC) – two sets of 392 bytes

CSIT 301 (Blum) 49

Capacity and Rate• The CD-DA sampling specs require

– 176400 bytes/second – 10584000 bytes/minute– 10336 kilobytes/minute– 10 megabytes/minute (actual data)

• That is, one minute of CD audio (uncompressed) corresponds to 10 MB.

• CD-DA specifies a capacity of 74-minutes of digital audio or approximately 747 MB of actual audio data.

CSIT 301 (Blum) 50

Fixing Mistakes

• CDs have a lot of ECC so that errors can be fixed. • If the data for a given sample cannot be recovered

using ECC, one can interpolate. Assume the bad sample is halfway between the previous and the next sample.

• Interpolation is not available to CDs used to store data, so they have even more space devoted to ECC.

CSIT 301 (Blum) 51

CD-DA Recap

• The CD-DA standard as set out in the “Red Book,” defines a sector or block of 3234 bytes.

• Of those 3234 bytes, – 2352 are actual audio data– 98 are control (analog of servo information,

synchronization and location)– 784 are EDC/ECC

CSIT 301 (Blum) 52

CD-DA Percentages• Each CD-DA block or sector is

– 72.7% actual audio data– 24.2% EDC/ECC– 3% control data

• For every 8 bits of data, there are 3 more bits of control/error data.

• If a CD-DA error cannot be corrected, one can interpolate.

CSIT 301 (Blum) 53

CD-ROM

• The red-book CD-DA standards were adapted by the “Yellow Book” standards to handle non-audio data, i.e. regular data files, programs, etc.

• These standards are for CD-ROMs, compact disc – read only memory –information written by the manufacturer and not changed by the user.

CSIT 301 (Blum) 54

CD-ROM Mode 1• CD-ROM Mode 1 starts with the basic CD-DA

sector division 3234 = 98 (control) + 784 (error)

+ 2352 (data)and devotes some of the data portion to additional error code and control yielding 3234 = 98 (control) + 784 (error)

+ 304 (more error/control) + 2048 (data).

CSIT 301 (Blum) 55

CD-ROM Mode 1 Percentages

• Each CD-ROM block or sector is – 63.3% actual data– 33.6% EDC/ECC– 3% control data

• More than one-third error detection and error correction code

CSIT 301 (Blum) 56

Less Data/Fewer Errors/More Control

• The CD-ROM standards impose more control because one must be able to locate data with more precision.

• The CD-ROM standard imposes more error detection and error correction because by the nature of the data it stores it does not have available the interpolation approach to dealing with errors that CD-DA does.

CSIT 301 (Blum) 57

Speeds• The 150 KB/s is the base data transfer rate for CD-ROM.

• Higher speeds are reported as multiplicative factors of this base: 2, 3, etc.

• Recall that as disc speeds got higher, they switched from CLV (constant data rate) to CAV (variable data rate).

• The latter data rates may be reported with the term “Max” to indicate that the reported data rate is the maximum of the range (i.e. When one is on the outer edge of the CD).

• Such drives must still support CLV at lower speeds so that they can play audio CDs.

CSIT 301 (Blum) 58

CSIT 301 (Blum) 59

The Other Speed Factor

• The data transfer rate is the rate for reading consecutive data. Another speed factor is average access time which is the typical time required to locate a “random” address.

• As with hard disks, this involves the radial positioning of the head (seek time) and the angular spinning of the disk (latency).

CSIT 301 (Blum) 60

CD-R• As typical files grew larger and larger, the

limitations of the floppy disk as a software/data delivery mechanism became evident.

• The CD-ROM had hundreds of times the capacity of a floppy, but was limited in that it was “read only.” The standards essentially required a manufacturing process to write data.

• So the CD-R standards were introduced. They are laid out in the orange book mainly by Phillips in 1990.

CSIT 301 (Blum) 61

CD-R

• CD-R (compact disc, recordable) are also sometimes known as CD-WORM (write once read many) or just CD-WO (write once).

• While the Yellow Book, Green Book and White Book outline variations in the logical overlay of the physical specifications laid out in the Red Book, the Orange book must outline new physical requirements that allow a user to record a CD.

• Basically the same logical overlay as CD-ROM will be maintained for compatibility.

CSIT 301 (Blum) 62

Changing Medium

• Recall that a CD-ROM is stamped from a master. The stamping provides the pits. When reading, the pits and distinguished from the lands because the lands yield specular reflection (clean, organized) while the pits yield diffuse reflection (scattered).– Think of light reflecting off a mirror versus light

reflecting a rippling body of water (pool, lake, etc.)

• So all that is needed is to produce this change in the way light is reflected.

CSIT 301 (Blum) 63

Before Recording (Burning)• A CD-R starts off with a plastic substrate. The

substrate is not flat, rather it has a wobbly spiral groove. – Think of it as lined paper, the lines guide us as to where

we will write the information.

• On top of the plastic is a photosensitive dye. • On top of that is the reflective layer (gold, silver

or aluminum alloy). • On top of that is a protective layer of plastic. • On top of that is the label.

CSIT 301 (Blum) 64

Before Burning

From http://entertainment.howstuffworks.com/cd-burner2.htm

CSIT 301 (Blum) 65

Photosensitive Dye

• The chemical between the plastic and the metal is photosensitive, meaning that it changes its properties when exposed to light. – The process is known as burning.

• In this case the light is laser light, the changes are permanent, and the important aspect here is that the changed property affects the way light is reflected.

CSIT 301 (Blum) 66

After Burning

CSIT 301 (Blum) 67

All at once?

• The recording is permanent but it does not necessarily have to be done all at once.

• If the recording is allowed to be done in more than one sitting, then the recording is said to be multi-session as opposed to single-session.

• Another term is Track-At-Once (TAO) versus Disc-At-Once (DAO).

CSIT 301 (Blum) 68

Table of Contents• A CD-ROM has a table of contents (TOC) at the

beginning. It serves a similar purpose to the file allocation table and root directory found on a hard disk, it allows the files to be found.– A.k.a. index of the disc.

• Newer so-called multi-session CDs allow data to be written in various sessions, that is for data to be appended (not overwritten) at a later time. – Such CDs have a table of contents for each session. – The new TOC contains the old info plus the new.– Such CDs cannot be read by ordinary drives unless they are

“finalized.”.

CSIT 301 (Blum) 69

Single Session vs. Multiple Session

• With single-session CDs, the TOC is easily located by the drive. Multi-session CDs drives need to be able to find the latest TOC.

• Many older CD drives do not have this capability.

• Reading a CD-RW requires a multi-session capability, so it is becoming standard.

CSIT 301 (Blum) 70

CD-R Drive• The burning of a CD requires a special laser,

different from the one in an ordinary CD-ROM drive used for reading.

• CD-Rs can typically handle many of the various logical formats (CD-DA, CD-ROM, CD-I, etc.)

• A CD-R drive can also read. Typically it reads at a higher speed than it writes.

• Writing a CD requires a steady flow of data and can be demanding. – Early on, simple CD-ROM drives were often

IDE/ATAPI but CD-R drives were more likely to be SCSI, which tend to perform better and allow other things to occur simultaneously.

CSIT 301 (Blum) 71

Keep that data flowing

• To keep the flow of data steady, a CD-R drive may use a buffer.

• Another approach is to make an image of the disc to be burned on the hard drive (collect all the files from their various locations, add the error code, etc.) and then have a nice, steady, fast continuous read of consecutive data.

CSIT 301 (Blum) 72

Usefulness of CD-R

• CD-Rs had floppies beat on capacity by a (multiplicative) factor of several hundred, but floppies could be written and re-written.

• For files that are in the editing/updating process, the ability to rewrite is crucial. – CD-Rs have come down in price, but they’re

too expensive to be thrown away regularly – let alone the impact that would have on the environment.

CSIT 301 (Blum) 73

CD-RW• CD-Rs are “write once” because the photo-sensitive dye is

permanently changed when it is written/burned. • In CD-RW this material is replaced with a phase-change

layer. – A phase is a state that a material can be in. For example, H2O can

be in one of three phases: ice (solid), water (liquid), stream (gas). – Materials may have several different solid phases.

• A phase is stable (the material can remain in a given phase indefinitely), but a phase change is reversible (heating for example may return the material to its original state).

CSIT 301 (Blum) 74

Dr Jekyll and Mr Hyde• The two phases in question are a matter of how

“organized” the material is. • In one phase, the material is a very orderly crystal

that reflects light specularly. • In the other phase, the material is disorderly and

reflects light diffusely. • Heating the material a little can give it a little bit of

movement and flexibility so it can organize. Heating it up a lot throws it into disorder, but it cools quickly (quenches) and remains in the disorderly state.

CSIT 301 (Blum) 75

The price one pays

• The differences in these phases is more subtle than the differences in CD-ROMs and CD-Rs.

• Thus a drive must have a more sensitive photo-detector in order to read a CD-RW.

• Many older (“legacy”) drives do not have such a sensitive detector and cannot read CD-RWs.

CSIT 301 (Blum) 76

Digital Versatile/Video Disk (DVD)

• The size of software and data files continues to grow, so the CD with its 650 MB capacity is becoming too limited.

• A newer, higher capacity alternative is the DVD which stands for either digital video disk or digital versatile disk. – Although some will now say DVD doesn’t

stand for anything.

CSIT 301 (Blum) 77

DVDs• A DVD is just a variation on a CD, information is

read from the disc by reflecting light from its surface.

• The differences between DVDs and CDs is a matter of speed and capacity (DVDs are better on both counts) and logical format.

• As with CDs there are various formats and one has to be careful about compatibility.– Many DVD standards are maintained by ECMA.

CSIT 301 (Blum) 78

ECMA

CSIT 301 (Blum) 79

DVD-R Standards Page

CSIT 301 (Blum) 80

DVD-R Standards Page (cont.)

CSIT 301 (Blum) 81

Viva la difference

• A different laser– A DVD laser has a wavelength of 636 nm or 650 nm

compared to a CD laser having a wavelength of 780 nm.

• The nm stands for nanometer, that’s 10-9 m, a billionth of a meter.

– With a smaller wavelength, one can “resolve” (distinguish) smaller/closer objects. In this case, the smaller wavelength allows the pits and the lands to be smaller and closer together on a DVD than on a CD.

CSIT 301 (Blum) 82

Waves with different wavelengths

CSIT 301 (Blum) 83

Electromagnetic spectrum

Red light has a smaller wavelength than IR (infrared). Blue light (used by Blu-Ray) has an even smaller wavelength.

←Wavelength getting smaller

CSIT 301 (Blum) 84

Smaller Pits Higher Density/Capacity

CSIT 301 (Blum) 85

DVD Pits

CSIT 301 (Blum) 86

Another Difference

• The Error Correction Code (ECC) used in DVDs is more efficient. – As with CDs the amount and type of ECC will

vary between DVDs used for multimedia and DVDs used for “regular” files.

• DVDs also use a somewhat larger area for recording.

CSIT 301 (Blum) 87

Result: Higher Capacity

• The previous factors result in a DVD having several times the capacity of a CD. – DVD capacity is approximately 4.7 GB

(minimum) compared to CD-ROM capacity of 650 MB – about seven times larger.

– Caution: In DVD standards GB means 109 (1,000,000,000) instead of 230 (1,073,741,824).

CSIT 301 (Blum) 88

Higher Speeds

• DVDs have a higher standard data transfer rate – 1.32 MB/s compared to 150 KB/s for CD-DA – about nine times faster. – This speed specification is for video viewing. When

DVDs are used for non-video data, they can be operated at higher speeds, which are reported as multiplicative factors of the standard: 2X, 3X etc.

– Older DVD-ROM drives used CLV, now they tend to use CAV. In the latter case, the maximum multiplicative factor is reported, e.g. 16X max.

CSIT 301 (Blum) 89

Sizes, Sides and Layers

• DVDs come in two standard sizes: diameter 80 mm or diameter 120 mm (standard CD size).

• DVDs can be single-sided (SS) or doubled-sided (DS), effectively two DVDs glued together.

• A DVD can be single layer (SL) or double layer (DL). – The upper layer is semi-transparent, so one can see

through to the second layer of data.

CSIT 301 (Blum) 90

Single Versus Double Layer

The laser is focused on the different layers at different times.

CSIT 301 (Blum) 91

Numbers and Capacities

• DVD-5: single-sided, single-layered 4.7GB

• DVD-9: single-sided, double-layered 8.5GB

• DVD-10: double-sided, single-layered 9.4GB

• DVD-14: double-sided, mixed layers 13.2GB

• DVD-18 double-sided, double-layered 17GB– Still uncommon

CSIT 301 (Blum) 92

Layers and Sides

CSIT 301 (Blum) 93

UDF

• There was some attempt to avoid the pitfalls of the CD situation (so many formats) and out of that came UDF. – Of course, they didn’t succeed, there a number of DVD

formats.

• UDF stands for Universal Disk Format. • “UDF, defined by the Optical Technology Storage

Association (OTSA), is a subset of ISO 13346, an interchange standard for non-sequential recording of data.”

CSIT 301 (Blum) 94

UDF (Cont.)

• It is a file system used for DVDs and optical media in general. – Some CDs can use it.

• It is “universal” in that all of the major DVD vendors have agreed to use it.

• It is also “universal” in that data files and multimedia files are not treated separately.

• It allows the operating system to understand what is on a DVD.

CSIT 301 (Blum) 95

Various Formats

• In addition to the different physical formats, there are a number of different application formats and the accompanying compatibility issues. – DVD+R, DVD+RW, DVD-RAM, DVD-R,

DVD-RW, DVD-ROM

• DVD drives are usually “backward compatible” in that they can read most CD formats.

CSIT 301 (Blum) 96

DVD-Video and DVD-ROM

• Analogous to CD-DA (for music) and CD-ROM (for data) are DVD-Video (for movies) and DVD-ROM (for data). – An DVD player may only be able to read DVD-

Video, whereas a DVD drive will be able to read DVD-ROM as well as DVD-Video.

• These standards are read only. The information is stamped or pressed onto the disc by a manufacturer.

CSIT 301 (Blum) 97

MPEG2• MPEG2 is part of the DVD-Video standard. It

describes how multimedia files can be compressed (50-to-1).

• MPEG stands for Moving Picture Experts Group. – MPEG is part of ISO.

• There are three major MPEG standards: MPEG-1, MPEG-2 and MPEG-4.

• The decoding can be done by software or hardware.

CSIT 301 (Blum) 98

MPEGMPEG Uses

1. Discrete Cosine Transform (DCT). 2. Quantization, selectively throwing away information that

won’t be missed (“lossy compression”). 3. Huffman coding, a lossless compression technique that

uses code encoding frequently occurring data with short codes and infrequently occurring data with long codes.

4. Motion compensated predictive coding: encode changes from one frame to the next rather than encoding each new frame in its entirety.

5. Bi-directional prediction like interpolation discussed in CD-DA.

CSIT 301 (Blum) 99

Recordable

• As with CD-R, making a recordable DVD requires some changes in the physical medium. – The writing is not done by pressing but by

exposing the DVD-R’s photo-sensitive dye layer to light and “burning” the information on it.

CSIT 301 (Blum) 100

Rewritable

• As with CDs, to achieve rewritability, one must replace the photosensitive material which is permanently burned with “phase change” material. – The phase change material in DVD RW means that

they do not reflect as strongly as DVD-ROM or DVD-R. This makes them harder to read.

– Sometime drives have trouble distinguishing between double layered DVDs and DVD-RW.

CSIT 301 (Blum) 101

The Competition

• There are three competing technologies for rewritable DVDs– DVD-R– DVD+R– DVD-RAM

CSIT 301 (Blum) 102

DVD-RW

• A.k.a. DVD-ER and DVD-R/W

• Can be written about 1000 times

• There is a distinction with DVD-RW discs– 1.1 do not support CPRM (Content Protection

for Removable Media)– 1.1B do support CPRM

• Apple and Compaq

CSIT 301 (Blum) 103

CPRM

• Content Protection for Removable Media (CPRM) enforces copy protection restrictions using a mechanism built into the storage medium itself.

• Based on broadcast encryption, the CPRM system would incorporate “tags” into storage media.

• Controversial, other alternative pursued.

CSIT 301 (Blum) 104

DMCA• Stands for Digital Millennium Copyright Act (a

update of copyright law law from 1998). – “It is a crime to circumvent anti-piracy measures that

are built into commercial software.”

– “It is a crime to manufacture, sell or distribute code-cracking devices that illegally copy software. However, it is not a crime to crack copyright protection devices in order to conduct encryption research, assess product interoperability or test the security of computer systems.”

– Etc.

CSIT 301 (Blum) 105

DVD-RAM

• Better access speeds • Can be written 100,000 times• Uses a cartridge (for better medium

protection)• Standard DVD drives don’t support the

cartridge. You may lose rewritability if you remove them from the cartridge.

• Hitachi, Panasonic and Toshiba

CSIT 301 (Blum) 106

DVD+RW

• Written to 1,000 times

• No cartridge

• Not officially a standard of the DVD Forum but backed by Sony and HP.

• Records video well.

• DVD+R is a write-once technology that is compatible with DVD+RW.

CSIT 301 (Blum) 107

DVD-Audio versus Audio CD

Sampling Rate Number of Levels

CD 44,100 Hz 216 = 65,536

DVD 192,000 Hz 224 = 16,777,216

CSIT 301 (Blum) 108

Is DVD-Audio overkill?

CSIT 301 (Blum) 109

References

• PC Hardware in a Nutshell, Thompson and Thompson

• http://www.pctechguide.com/10dvd.htm

• http://www.webopedia.com

• http://www.pcguide.com

• http://entertainment.howstuffworks.com/cd-burner2.htm