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More on CDs and DVDs

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Extended Architecture

• While the original Mode 2 standard was not used, a variation on it allowed regular data and audio or video data to be stored together.

• The Extended Architecture standard CD-ROM XA allows the two types of data to be “interleaved” on the same track.

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Extended Architecture• The Extended Architecture has two modes

– Mode 2, Form 1, which is like Mode 1 and is used for regular data files

– Mode 2, Form 2, which is like Mode 2 and is used for compressed audio/video files.

• The two modes allowed for the mixing (interleaving of data).

• The use of a CD-ROM XA disc requires a special drive. The drive understood the two formats being mixed. It also might be able to uncompress the data “on the fly.”

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CD-Interactive

• An extension of the CD-ROM-XA idea was the CD-i (i for interactive). In CD-I the disk stores data in different formats, but the data is related. One could mix programs and text and audio and video together to create a multimedia experience for the user that was controlled by the user.

• The CD-I format was led by Philips and Sony (the same two that gave us the CD-DA standards) and are contained in the Green Book.

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Bridge CD

• Another set of standards that spanned the CD-ROM-XA and CD-I technologies was developed in the White Book.

• CDs of this format are sometimes called bridge CDs since they work with both technologies.

• The category includes Bridge the Kodak Photo CD format and the Video CD format.

• Is being replaced by DVDs.

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Video CD

• Using MPEG compression one can put a 74-minute movie (video plus audio) in the same space used by CD-DA for just audio.

• So-called video CDs or VCDs were of limited quality, required a special player and have been surpassed by DVDs.

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Photo CD• The Photo CD is an example of CD-I technology

developed by Kodak specially for photographic data.

• Since under normal circumstances one is not going to make a master Photo CD and create from it many copies. The Photo CD standard are found in the Orange Book, which sets out the standards for CD-R, recordable CDs.

• But they can be written following the CD-I standards.

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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.

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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.

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Changing Medium

• Recall that a CD-ROM is stamped from a master. The stamping provides the pits. When reading, he 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.

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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.

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Before Burning

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

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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.

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After Burning

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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).

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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.”.

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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.

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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.

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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 have a nice, steady, fast continuous read of consecutive data.

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Compatibility• With differences in physical makeup (CD-ROM vs.

CD-R vs. CD-RW) as well as differences in how writing is done (single-session vs. multi-session) and differences in logical overlay (CD-DA, CD-ROM, CD-I, etc.), compatibility is an issue with CD drives and CDs. – Another difference is whether a drive can extract CD-DA

data or just play it.

• Compatibility issues are being resolved, newer CD players tend to accept a wider variety of formats, but it remains an issue to be aware of.

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Compatibility Table

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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.

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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).

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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.

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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.

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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.

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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.

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ECMA

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DVD-R Standards Page

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DVD-R Standards Page (cont.)

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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.

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Waves with different wavelengths

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Smaller Pits Higher Density/Capacity

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DVD Pits

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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.

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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).

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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.

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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.

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Single Versus Double Layer

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

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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

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Layers and Sides

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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 VDV

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.”

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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.

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MicroUDF and UDF Bridge

• Actually DVDs use a subset of UDF, called MicroUDF.

• Microsoft did not initially support MicroUDF and so an intermediate standard UDF Bridge is thrown into the mix. – UDF Bridge is a hybrid of UDF and ISO 9660.

• UDF specifies a file size limit, a file naming scheme and provides a directory so that files can be found.

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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.

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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.

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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.

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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.

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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.

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DVD-R(A) and DVD-R(G)

• DVD-R (Authoring) – Used more by professionals, not generally

available to the public– Used for “mastering”

• DVD-R (General)– Used by the public

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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.

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The Competition

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

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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

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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.

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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.

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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

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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.

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Compatibility Table

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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

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Is DVD-Audio overkill?

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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