20 Optical Storage Devices by besube

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Optical Storage Devices
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Optical Storage Devices


•   CD-ROM and DVD technologies use high-capacity optic media

    in the form of a silvery platter that holds digital data that is

    decoded by striking it with a laser beam.

•   DVD drives can also read CD-ROM.

•   A single CD can store an entire software package.

•   The following table lists the advantages of storing data on a

    CD.

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Optical Storage Devices

   Advantage                                                                        Description

   Large storage capacity                                                           Up to 650 MB of data fit on a
   compared to floppy-type media                                                    single 5-inch disc.

   Portability                                                                      The CD is a portable medium.

   Data cannot be changed                                                           A CD is read-only, which
                                                                                    prevents accidental erasure of
                                                                                    programs or files.
   Sturdiness                                                                       Durable than the standard 5.25-
                                                                                    inch or 3.5-inch disks.
   Special capabilities                                                             CD-ROMs are audio-capable,
                                                                                    allowing special compression
                                                                                    of audio, image, and video data.

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Development of the CD

•   The development of the computer CD roughly paralleled the
    audio (music) CD:
    – In 1979, the CD, as a storage medium, was introduced in the audio
      industry.
    – In 1985, the CD came to the computer industry. Development was
      slow because the hardware was too expensive for most
      manufacturers and users.
    – In 1991, the CD-ROM/XA standard was enhanced, and multimedia
      requirements for hardware were specified.
    – In 1993, high-quality video playback came to the computer.
    – Price of CD-ROM drives continues to drop, while their speed
      climbs.

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CD-ROMs


•   CD-ROM, or compact disc read-only memory, is an optical

    read-only storage medium based on the original CD-DA (digital

    audio) format.

•   Formats, such as CD-R (CD recordable) and CD-RW (CD-

    rewritable), are expanding the compact disc's capabilities by

    making it writable.


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CD-ROMs (contd.)


•   CD-ROM is a read-only optical storage medium capable of

    holding up to 74 or 80 minutes of high fidelity audio

    (depending on the disc used), or up to 682MB (74-minute disc)

    or 737MB (80-minute disc) of data, or some combination of the

    two, on one side (only the bottom is used) of a 120mm (4.72-

    inch) diameter, 1.2mm (0.047 inches) thick plastic disc.




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CD-ROMs (contd.)


•   Two main types of recordable CD drives and discs are

    available, called CD-R (recordable) and CD-RW (rewritable).

•   The CD-RW discs are 1.5-4 times more expensive than CD-R

    discs, only half as fast (or less) as CD-R discs, and won't work

    in all CD audio or CD-ROM drives, thus people usually write to

    CD-R media in their CD-RW drives.


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CD-ROM Technology

•   It store data as a series of 1s and 0s
•   Instead of using magnetic energy to read and write data, CD
    readers and writers use laser energy.
•   There are two major advantages to using lasers:
     – There is no physical contact between the surface of the CD and
        the reading device.
     – The diameter of the laser beam is so small that storage tracks can
        be written very close together, allowing more data to be stored in
        a smaller space.



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Structure of CD-ROM

•   A CD platter is composed of a reflective layer of aluminum
    applied to a synthetic base that is composed of polymers.
•   A layer of transparent polycarbonate covers the aluminum.
•   A protective coating of lacquer is applied to the surface to
    protect it from dust, dirt, and scratches.




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Structure of CD-ROM (contd.)

•   Data is written by creating pits and lands on the CD's surface.
•   A pit is a depression on the surface, and a land is the height of
    the original surface.
•   The transition from a land to a pit or a pit to a land represents a
    binary character of 1.
•   Lands and pits represent binary 0.




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                                                                                                                                                                  Cont…
Structure of CD-ROM (contd.)

•   There are around 4 to 5 million pits per CD, arranged in a

    single outward-running spiral (track) around 3.75 miles (6

    kilometers) long.

•   The distance between each track is 1.6 microns of a meter.




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Reading Operation from CD-ROM

•   Reading the information back is a matter of bouncing a low-

    powered laser beam off the reflective layer in the disc.

•   Laser shines a focused beam on the underside of the disc, and

    a photosensitive receptor detects when the light is reflected

    back.

•   When the light hits a land (flat spot) on the track, the light is

    reflected back; however, when the light hits a pit (raised

    bump), no light is reflected.

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Reading Operation from CD-ROM (contd.)

•   As the disc rotates over the laser and receptor, the laser
    shines continuously while the receptor sees what is essentially
    a pattern of flashing light as the laser passes over pits and
    lands.
•   Each time the laser passes over the edge of a pit, the light
    seen by the receptor changes in state from being reflected to
    not reflected or vice versa.
•   Microprocessors in the drive translate the light/dark and
    dark/light (pit edge) transitions into 1 bits, translate areas with
    no transitions into 0 bits, and then translate the bit patterns
    into actual data or sound.
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Drive Mechanical Operation

•   Laser diode emits a low-
    energy infrared beam
    toward a reflecting mirror.
•   The servo motor, on
    command from the
    microprocessor, positions
    the beam onto the correct
    track on the CD-ROM by
    moving the reflecting
    mirror.
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Drive Mechanical Operation (contd.)

•   When the beam hits the disc, its refracted light is gathered and
    focused through the first lens beneath the platter, bounced off
    the mirror, and sent toward the beam splitter.

•   The beam splitter directs the returning laser light toward
    another focusing lens.

•   Last lens directs the light beam to a photo detector that
    converts the light into electric impulses.

•   These incoming impulses are decoded by the microprocessor
    and sent along to the host computer as data.

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CD Drive Speed

•   CDs originally were designed to record audio, the speed at
    which the drive reads the data had to be constant.
•   To maintain this constant flow, CD-ROM data is recorded
    using a technique called constant linear velocity (CLV).
•   The track is spiral that is wound more tightly near the centre of
    the disc and the disc must spin at various rates to maintain the
    same track linear speed.
•   Speed of rotation in a 1x drive (1.3 meters per second is
    considered 1x speed) varies from 540rpm when reading the
    start (inner part) of the track down to 212rpm when reading the
    end (outer part) of the track.
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CD Drive Speed (contd.)

•   A drive that spins twice as fast was called a 2x drive, one that
    spins four times faster was called 4x.
•   At higher speeds than this, it became difficult to build motors
    that could change speeds (spin up or down) as quickly as
    necessary when data was read from different parts of the disc.
•   Most drives rated faster than 12x spin the disc at a fixed
    rotational, rather than linear speed which is termed constant
    angular velocity (CAV).
•   Speeds are usually expressed as a multiple of the original
    audio CD data transfer rate (150 Kb/sec).
•   CD-ROM drives have been available in speeds from 1x up to
    56x and beyond.

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CD-ROM File Systems

•   Manufacturers of early CD-ROM discs required their own
    custom software to read the discs.
•   In 1985-1986, several companies got together and published
    the High Sierra file format specification, which finally enabled
    CD-ROMs for PCs to be universally readable.
•   Several file systems are used on CDs now which are as
    follows:
    – High Sierra
    – ISO 9660 (based on High Sierra)
    – Joliet
    – UDF (Universal Disk Format)
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High Sierra

•   In 1985, representatives from TMS, DEC, Microsoft, Hitachi,
    LaserData, Sony, Apple, Philips, 3M, Video Tools, Reference
    Technology, and Xebec met at what was then called the High
    Sierra Hotel and Casino in Lake Tahoe, Nevada, to create a
    common logical format and file structure for CD-ROMs.

•   This agreement enabled all drives using the appropriate driver
    (such as MSCDEX.EXE supplied by Microsoft with DOS) to
    read all High Sierra format discs, opening the way for the mass
    production and acceptance of CD-ROM software publishing.

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ISO 9660

•   ISO 9660 was released in 1988 and was based on the work
    done by the High Sierra group.
•   ISO 9660 has three levels of interchange that dictate the
    features that can be used to ensure compatibility with different
    systems.
•   ISO 9660 Level 1 is the lowest common denominator of all CD
    file systems and is capable of being read by almost every
    computer platform, including Unix and Macintosh.
•   Level 2 interchange rules have the same limitations as Level 1,
    except that the filename and extension can be up to 30
    characters long.
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ISO 9660 (contd.)

•   Level 3 interchange rules are
    the same as Level 2 except
    that files don't have to be
    contiguous.

•   ISO 9660 data starts at 2
    seconds and 16 sectors into
    the disc, which is also
    known as logical sector16 of
    track one.

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ISO 9660 (contd.)


•   This data identifies the location of the volume area-where the

    actual data is stored.


•   System area also lists the directories in this volume as the

    volume table of contents (VTOC), with pointers or addresses to

    various named areas.




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Joliet


•   Joliet is an extension of the ISO 9660 standard developed by


    Microsoft for use with Windows 95 and later.


•   Joliet enables CDs to be recorded using filenames up to 64


    characters long, including spaces and other characters from


    the Unicode international character set.


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Universal Disk Format

•   UDF is a relatively new file system created by the Optical
    Storage Technology Association (OSTA) as an industry-
    standard format for use on optical media such as CD-ROM and
    DVD.

•   UDF has several advantages over the ISO 9660 file system
    used by standard CD-ROMs but is most noted because it is
    designed to work with packet writing, a technique for writing
    small amounts of data to a CD-R/RW disc, treating it much like
    a standard magnetic drive.
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Interface Type

•   Drive's interface is the physical connection of the drive to the
    PC's expansion bus.

•   Types of interfaces available for attaching a CD-ROM, CD-R, or
    CD-RW drive to your system are
    – ATA/ATAPI (AT Attachment/AT Attachment Packet Interface)

    – Parallel port

    – SCSI/ASPI (Small Computer System Interface/Advanced SCSI
        Programming Interface)

    – USB port
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Media Types

•   Writable CDs
    – CD originally was conceived as a read-only device, these days
        one easily can create their own data and audio CDs.
    – In CD-R media, after you fill a CD-R with data, it is permanently
        stored and can't be erased.
    – Write-once limitation makes this type of disc less than ideal for
        system backups or other purposes in which it would be preferable
        to reuse the same media over and over.
    – When first introduced, there were many CD-R-only drives;
        however, today most recordable CD drives are both CD-R and CD-
        RW in one.
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Media Types (contd.)

•   CD-R
    – CD-Rs function using the same principle as standard CD-ROMs,
      by bouncing laser light off the disc and tracking the changes in
      reflectivity when pit/land and land/pit boundaries are encountered.
    – To record on a CD-R disc, a laser beam of the same wavelength
      (780nm) as is normally used to read the disc, but with 10 times the
      power, is used to heat up the dye.
    – The high temperature of the laser burns the organic dye, causing
      it to become opaque.
    – When read, this prevents the light from passing through the dye
      layer to the gold and reflecting back, having the same effect of
      cancelling the laser reflection that an actual raised pit would on a
      normal stamped CD.
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Media Types (contd.)

•   CD-RW
    – In early 1996, an industry consortium that included Ricoh, Philips,
      Sony, Yamaha, Hewlett-Packard, and Mitsubishi Chemical
      Corporation announced the CD-RW format.
    – Ricoh was the first manufacturer to introduce a CD-RW drive in
      May of 1996 which was a 2/2/6 (2x record, 2x rewrite, 6x read)
      rated unit.
    – CD-RW drives are fully backward compatible with CD-R drives and
      can read and write the same CD-R media with the same
      capabilities.
    – With packet-writing software, they can even be treated like a giant
      floppy disk, where you can simply drag and drop or copy and
      delete files at will.
    – CD-RW media being rewritable and costing a bit more, they also
      are writable at about half (or less) the speed of CD-R discs.
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Recording Software

•   A difficulty with CD-R/RW devices is that they require special
    software to write them.
•   Most cartridge drives and other removable media mount as
    standard devices in the system and can be accessed exactly
    like a hard drive, the CD-R/RW drive uses special CD-ROM
    burning software to write to the disc.
•   Software assembles the directory information, burns it onto
    the CD, opens each file on the CD, and copies the data directly
    from the original source.
    E.g Nero is an example of such software.
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Choosing the Right CD-ROM

•   One can select the right one for needs, depending upon the
    following characteristics:
    – Physical Characteristics

    – DISC Loading

    – INTERNAL OR EXTERNAL

    – Data Transfer Rate

    – Access Time

    – Caching

    – Buffers
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DVD

•   What is DVD

•   DVD, which stands for
    Digital Versatile Disc, is
    one of optical disc
    storage technology. It's
    essentially a bigger,
    faster CD that can hold
    video as well as audio
    and computer data.

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DVD (contd.)

                                               DVD different from CD
                                                       CD                                                            DVD
 Disc Diameter                                         120 mm                                                        120mm and 80mm
 Disc Thickness                                        1.2mm                                                         1.2mm
 Disc Structure                                        Single substrate                                              Two bonded 0.6 mm substrates
 Laser Wavelength                                      780mm (infrared)                                              650 and 635 nm (red)
 Track Pitch                                           1.6um                                                         0.74um
 Shortest pit/and length                               0.83um                                                        0.4um
 Data Layers                                           1                                                             1 or 2
 Data Capacity                                         Aprox. 680 megabytes                                        Single layer: 4.7GB ×2(side)
                                                                                                                   Dual layer: 8.5 GB × 2(side)
 Reference Data Rate                                   153.6 kilobytes/sec 1,108                                   kilobytes/sec, nominal
                                                       to 176.4 kilobytes/sec


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How DVD works


•   A DVD stores data in little pits in a single spiraling track on a

    reflective metal surface embedded in plastic.

•   A laser in the drive reads the pits as zeros.

•   The challenge in developing DVD was simple; increase data

    capacity by packing as many pits as possible onto a disc;

    using inexpensive technology.


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                                                                                                                                                                   Cont….
How DVD works (contd.)


Reasons For Increase In Capacity

•   Smaller pit length.

•   Tighter tracks.

•   Slightly larger data area.

•   More efficient channel bit modulation.

•   More efficient error correction.



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How DVD works (contd.)


Sides of DVD

•   SSSL (Single Sided Single Layer)

•   SSDL (Single Sided Double Layer)

•   DSSL (Double Sided Single Layer)

•   DSDD(Double Sided Double Layer)




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Features Of DVD

• Durability (no wear from playing, only from physical damage).
• Not susceptible to magnetic fields.
• Resistant to heat.
• Compact size (easy to handle and store, players can be
 portable, replication is cheaper).
• Connectivity is similar to that of CD-ROM drives: EIDE (ATAPI),
 SCSI-2, etc.
• All DVD-ROM drives have audio connections for playing audio
 CDs.


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Features Of DVD (contd.)


Speeds Of DVD

•   Seek time of 150-200ms.

•   Access time of 200-250ms.

•   Data transfer rate of 1.3 MB/s with burst transfer rates of upto

    12 MS/s or higher.




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Features Of DVD (contd.)

Recordable Versions Of DVD

•   DVD-R

•   DVD-RAM

•   DVD+RW




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Features Of DVD (contd.)

DVD-R

•   DVD-R uses organic dye polymer technology like CD-R and is
    compatible with almost all DVD drives.




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DVD-RAM


•   DVD-RAM use technology that is not compatible with current

    drives (because of reflectivity differences, and minor format

    differences).

•   A wobbled groove is used to provide clocking data, with marks

    written in both the groove and the land between grooves.




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Features Of DVD (contd.)


•   Single-sided DVD-RAM discs come with or without cartridges.

    There are two types of cartridges: type 1 is sealed, type 2

    allows the disc to be removed.

•   Double-sided DVD-RAM discs will be available in sealed

    cartridges only.




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DVD+RW

•   DVD Phase-Change Rewritable, called DVD+RW without the
    blessing of the DVD Forum, is a competing erasable format
    announced by Philips, Sony, Hewlett-Packard and others
    based on CD-RW technology. DVD+RW drives will read DVD-
    ROMs and CDs, but are not compatible with DVD-RAM.

•   DVD Production.

•   Development Replication.

•   DVD-ROMs can be developed with traditional multimedia
    software tools such as Macromedia Director, and C++.

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DVD+RW (contd.)                                                                                                                                                 Cont….



•   Replication Usually done by large plants. Plants provide

    ‘check disc’ for testing before mass duplication

•   DVD Video Development

•   Encoding

•   Authoring (Design,Layout, and Testing)

•   Premastering (Formatting a disk image)



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DVD+RW (contd.)

•   Most scratches will cause minor channel data errors that are
    easily corrected.

•   A common misperception is that a scratch will be worse on a
    DVD than on a CD because of higher storage density and
    because video is heavily compressed. DVD data density is
    physically four times that of CD-ROM, so it's true that a scratch
    will affect more data. But DVD error correction is at least ten
    times better and more than makes up for the density increase.



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DVD+RW (contd.)


•   It's also important to realize that MPEG-2 and Dolby Digital

    compression are partly based on removal or reduction of

    imperceptible information, so decompression doesn't expand

    the data as much as might be assumed.




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DVD Video

•   DVD is vastly superior to videotape and generally better than
    laser-disc.

•   However, quality depends on many production factors. Until
    compression experience and technology improves we will
    occasionally see DVD's that are inferior to laser-discs.

•   Also, since large amounts of video have already been encoded
    for Video CD using MPEG-1, a few low-budget DVD's will use
    that format (which is no better than VHS) instead of higher-
    quality MPEG-2.

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The Interactive Features

•   DVD-Video players (and software DVD-Video navigators)
    support a command set that provides interactivity.

•   The main feature is menus, which are present on almost all
    discs to allow content selection and feature control. Each
    menu has a still-frame graphic and up to 36 highlightable,
    rectangular "buttons".

•   Remote control units have four arrow keys for selecting
    onscreen buttons, plus numeric keys, select key, menu key,
    and return key.

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The Interactive Features (contd.)

•   Additional material for camera angles and seamless branching
    is interleaved together in small chunks.

•   The player jumps from chunk to chunk, skipping over unused
    angles or branches, to stitch together the seamless video.

•   Since angles are stored separately, they have no direct effect
    on the bit-rate but they do affect the playing time.

•   Adding 1 camera angle for a program roughly doubles the
    amount of space it requires there by cutting the playtime in
    half.

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Multiple ratings (Parental Lockout)


•   This feature, would allow the viewer to choose between a R

    rated or a PG-13 rated cut of the same film, with the R rated

    material electronically skipped over while watching the disc.

•   Parental Lockout can be set to prevent the disc from playing at

    all without a password set by the parents.




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Regional codes, "Country codes", or
"Zone locks”

•   Each DVD player is given a code for the region in which it's
    sold. The player will refuse to play discs that are not allowed in
    that region.

•   This means that discs bought in one country may not play on
    players bought in another country.

•   Regional codes are entirely optional Discs without codes will
    play on any player in any country.

•   It's not an encryption system, it's just one byte of information
    on the disc that the player checks.

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                                                                                                                                                                         Revision no.: PPT/2K403/02




Can DVD record from VCR/TV/etc.

•   The minimum requirement for reproducing audio and video on
    DVD is an MPEG video stream and a PCM audio track.

•   Basic DVD control codes are also needed. At the moment it's
    difficult in real time to encode the video and audio, combine
    them with DVD-V info, and write the whole thing to DVD.

•   Even if you could do all this in a home recorder, it would be
    extremely expensive.

•   It's possible the first home DVD recorders will require a digital
    source of already-compressed audio and video.

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                                                                                                                                                                         Revision no.: PPT/2K403/02




Capacities Of DVD

•   DVD (8cm, SS/SL): 1.36 (1.4 G), about half an hour

•   DVD (8cm, SS/DL): 2.48 GB (2.7 G), about 1.3 hrs.

•   DVD (8cm, DS/SL): 2.72 GB (2.9 G), about 1.4 hrs.

•   DVD (8cm, DS/DL): 4.95 GB (5.3 G), about 2.5 hrs.

•   DVD (12cm, SS/SL): 4.38 GB (4.7 G) of data, over 2 hrs. of video

•   DVD (12cm, SS/DL): 7.95 GB (8.5 G), about 4 hrs.

•   DVD (12cm, DS/SL): 8.75 GB (9.4 G), about 4.5 hrs.

•   DVD (12cm, DS/DL): 15.90 GB (17 G), over 8 hrs.

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                                                                                                                                                                        Revision no.: PPT/2K403/02




Capacities Of DVD (copied.)                                                                                                                                    Cont. …



• DVD-R (8cm, SS/SL): 1.15 GB (1.23 G)

• DVD-R (8cm, DS/SL): 2.29 GB (2.46 G)

• DVD-R (12cm, SS/SL): 3.68 GB (3.95 G)

• DVD-R (12cm, DS/SL): 7.38 GB (7.9 G)

• DVD-RAM (12cm, SS/SL): 2.40 GB (2.58 G)

• DVD-RAM (12cm, DS/SL): 4.80 GB (5.16 G)



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                                                                                                                                                                         Revision no.: PPT/2K403/02




Notation and units

•   There's confusion of units of measurement in the DVD world.

•   For example, a single-layer DVD holds 4.7 billion bytes (G
    bytes), not 4.7 gigabytes (GB). It only holds 4.38 gigabytes.

•   Likewise, a double-sided, dual-layer DVD holds only 15.90
    gigabytes, which is 17 billion bytes.

•   The problem is that "kilo," "mega," and "giga" generally
    represent multiples of 1000 (10^3, 10^6, and 10^9), but when
    used in the computer world to measure bytes they generally
    represent multiples of 1024 (2^10, 2^20, and 2^30).

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                                                                                                                                                                         Revision no.: PPT/2K403/02




Notation and units (contd.)


•   Most DVD figures are based on multiples of 1000, in spite of

    using notation such as GB and KB/s that traditionally have

    been based on 1024

•   To get an unambiguous notation is to use Kbps for thousands

    of bits/sec, Mbps for millions of bits/sec, KB for 1024 bytes,

    MB for 1,048,576 bytes, and GB for 1,073,741,824 bytes. GB

    means gigabytes (2^30), G means billions of bytes (10^9)

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                                                                                                                                                                         Revision no.: PPT/2K403/02




Exercise

•   Exercise 20.1 Identification Optical Storage Device Parts




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