More on CDs by wpr1947


									            More on CDs and DVDs

CSIT 301 (Blum)                    1
                  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
• The Extended Architecture standard CD-
  ROM XA allows the two types of data to be
  “interleaved” on the same track.

CSIT 301 (Blum)                              2
                  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.”
CSIT 301 (Blum)                                               3
• 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.
CSIT 301 (Blum)                                         4
                  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.
• Replaced by DVDs.

CSIT 301 (Blum)                                    5
                  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.

CSIT 301 (Blum)                                6
                  Photo CD
• The Photo CD is an example of CD-I technology
  developed by Kodak specially for photographic
• 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

CSIT 301 (Blum)                                      7
• 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

CSIT 301 (Blum)                                   8
• 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)                                   9
                  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
     – 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)                                                 10
       Before Recording (Burning)
• A CD-R starts off with a plastic substrate. The
  substrate is not flat, rather it has a wobbly spiral
     – 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)                                                11
                   Before Burning


 CSIT 301 (Blum)                                         12
                  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

CSIT 301 (Blum)                                            13
                  After Burning

CSIT 301 (Blum)                   14
                  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
• Another term is Track-At-Once (TAO)
  versus Disc-At-Once (DAO).

CSIT 301 (Blum)                                  15
                  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)                                            16
        Single Session vs. Multiple
• With single-session CDs, the TOC is easily
  located by the drive. Multi-session CDs
  drives need to be able to find the latest
• Many older CD drives do not have this
• Reading a CD-RW requires a multi-session
  capability, so it is becoming standard.

CSIT 301 (Blum)                                17
                   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)                                             18
              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)                                   19
• 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.
CSIT 301 (Blum)                                                20
                  Compatibility Table

CSIT 301 (Blum)                         21
                  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
CSIT 301 (Blum)                                      22
• CD-Rs are “write once” because the photo-
  sensitive dye is permanently changed when it is
• 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)                                               23
              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)                                            24
                  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

CSIT 301 (Blum)                               25
      Digital Versatile/Video Disk
• 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)                                 26
• A DVD is just a variation on a CD, information is
  read from the disc by reflecting light from its
• 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)                                      27

CSIT 301 (Blum)          28
             DVD-R Standards Page

CSIT 301 (Blum)                     29
   DVD-R Standards Page (cont.)

CSIT 301 (Blum)                   30
                   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
           • The nm stands for nanometer, that’s 10-9 m, a billionth of a
     – 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)                                                             31
                  Waves with different


CSIT 301 (Blum)                          32
          Electromagnetic spectrum

                                ←Wavelength getting smaller

Red light has a smaller wavelength than IR (infrared). Blue
light (used by Blu-Ray) has an even smaller wavelength.
CSIT 301 (Blum)                                               33
              Smaller Pits  Higher

CSIT 301 (Blum)                       34
                  DVD Pits

CSIT 301 (Blum)              35
                  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

CSIT 301 (Blum)                                      36
             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)                                      37
                  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)                                              38
             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
     – The upper layer is semi-transparent, so one can see
       through to the second layer of data.

CSIT 301 (Blum)                                              39
       Single Versus Double Layer

  The laser is focused on the different layers at different
CSIT 301 (Blum)                                               40
            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)                             41
                  Layers and Sides

CSIT 301 (Blum)                      42
• 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
• 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)                                            43
                   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)                                       44
       MicroUDF and UDF Bridge
• Actually DVDs use a subset of UDF, called
• 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.

CSIT 301 (Blum)                                       45
                  Various Formats
• In addition to the different physical formats,
  there are a number of different application
  formats and the accompanying
  compatibility issues.
       DVD-RW, DVD-ROM
• DVD drives are usually “backward
  compatible” in that they can read most CD
CSIT 301 (Blum)                                46
      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)                                 47
• MPEG2 is part of the DVD-Video standard. It
  describes how multimedia files can be compressed
• MPEG stands for Moving Picture Experts
     – 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
CSIT 301 (Blum)                                  48
     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)                                              49
• As with CD-R, making a recordable DVD
  requires some changes in the physical
     – 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

CSIT 301 (Blum)                                          50
        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

CSIT 301 (Blum)                                    51
• 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)                                              52
                  The Competition
• There are three competing technologies for
  rewritable DVDs
     – DVD-R
     – DVD+R
     – DVD-RAM

CSIT 301 (Blum)                                53
• 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)                                      54
• 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)                               55
• 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
     – Etc.

CSIT 301 (Blum)                                                56
• Better access speeds
• Can be written 100,000 times
• Uses a cartridge (for better medium
• 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)                              57
• 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)                            58
                  Compatibility Table

CSIT 301 (Blum)                         59
    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)                                      60
            Is DVD-Audio overkill?

CSIT 301 (Blum)                      61
• PC Hardware in a Nutshell, Thompson and
CSIT 301 (Blum)                            62

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