A Guide to PC Hardware Maintenance and Repair

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Chapter 16 Multimedia Computerized Home
Entertainment
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Objectives

• To see how optical drives store and retrieve data
• To learn about a couple of new file systems used
  by optical media
• To look at various types of optical disks
• To see what make a sound card do what it does

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The Components of Multimedia

• An optical drive
• The CD Family
• The DVD Family
• Sound cards and Speakers

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The Introduction of the CD

• First developed as an audio device
• Introduced to computers to store large amounts of
  data
• Driven primarily by the gaming market

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Understanding CD Speed Ratings

• The first computer CD released by Philips was
  capable of 150Kb/s throughput
• When Sony developed a drive capable of 300Kb/s
  they advertised it as the 2x CD-ROM
• The naming pattern stuck

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How the CD Works (some terms)

• Pits
• Lands
• Optical Stylus
• Photoelectric Cell (PEC)
• Servo
• Digital Analog Converter (DAC)

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Pits and Lands

• Data is encoded onto the surface of a
  conventional CD by etching holes into the surface
  of an aluminum layer
• The holes are called pits all unmarked aluminum
  is land
• Pits are laid out in tracks, just like on a hard
  disk

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The Optical Stylus

• Named after the old playback needle on a
  turntable of yesteryear. (Dad? Whats a
  turntable?)
• Shines a 780 nanometer infrared laser, split into
  three beams, onto surface of CD
• Land reflects laser back pits dont

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Photoelectric Cell

• As the laser beam crosses the pits and lands the
  lands, intersected by pits results in a reflected
  beam of pulsating light
• The photoelectric cell converts the light to
  electrical energy
• The pulses of energy are the encoded data

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The Servo Motor

• To read the data accurately, the stylus must stay
  on the track
• On either side of each track is a 1.6 nanometer
  strip of land
• The center beam of the stylus is supposed reflect
  a pulsating beam. The two on the outside are not
• If either outside beam pulsates, the servo motor
  repositions the stylus back on track

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The DAC

• The pulsating electrical current passes onto the
  DAC where it is converted into an analog data
  stream
• The analog signal is then transmitted to the
  device requesting the data

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Optical File Formats

• Compact Disk Digital Audio (CDDA)
• Used by the recording industry to record music
  CDs
• Used in mixed format CDs that hold both music and
  digital data
• Compact Disk File System
• Used for storing digital data

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CDDA

• An analog signal is fed into a device that takes
  digital samples and converts the sample into a
  16-bit stream of data (chop)
• The industry standard for sample rate is 44,100
• 147 chops are stored in a 2,353-bit sector
• Data throughput for an audio CD is 176,400 Kb/s

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CDFS

• Audio files dont care if a bit or two is lost in
  conversion, but data files do
• 352 bits of the CDDA sector are set aside for
• 48 bits for Error Detection Code
• 302 bits as Synchronization bits
• This leaves a 2,000 bit sector for data

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CD Data Access Methods

• CLV
• CAV
• Hybrid

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CLV

• Constant Linear Velocity
• Since there are more sectors in the outside
  tracks than on the inside, data transfer rates
  increase as the stylus moves to the center of the
  disk
• CLV adjusted motor speed to change the rotational
  speed of the disk as the stylus moves towards
  center

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CAV

• Constant Angular Velocity
• Rotational speed of the disk remains constant
• The drive electronics adjust to the higher data
  throughput as the stylus moves to center
• CAV drives advertise speeds like 24/48x

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Hybrid drives

• Employ CAV for the out 1/3 of the disk
• Employ CLV for the inner 2/3 of the disk

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CD Loading Mechanisms

• Tray
• Inexpensive, but prone to breaking
• Caddy
• Expensive, but protects the disk better
• Slot
• Cheap and easy to use, but can play havoc on the
  CD

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The Descendants of CD

• CDR
• CD-RW
• DVD
• Various Recordable DVD formats

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CDR

• CD Recordable
• Uses pthalocyanine dye instead of aluminum for a
  substrate
• Two-power laser
• High-power beam burns pits into dye during record
  process
• Low-power beam is used for playback

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CD-RW

• CD Rewriteable
• Recording surface is an allow of silver,
  antimony, tellurium and indium
• Are you SURE you want to be throwing these into
  the city dump???
• At medium heat, the alloy melts, at high heat it
  crystallizes
• Three-power laser
• Low power for playback, high power to record and
  medium power to erase

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Digital Video Disk (DVD)

• Twice as many tracks and twice as many sectors
  per track as a CD
• Up to two recording layers can be placed on
  either side of DVD
• Double-sided DVDs separate recording layers with
  a microscopically thin layer of gold

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Sound Cards

• Convert analog sound to digital signals and vice
  versa
• A chip called an Analog/Digital Converter (ADC)
  converts sound waves to digital format
• A typical DAC coverts digital audio to analog
• Sound cards generally have 2 to 4 1/8 audio
  jacks and a 15-pin MIDI connector

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The Electronics of the Sound Card

• An old sound card had enough chips to supply six
  guys watching the Super Bowl
• Inexpensive sound cards of today have a single
  Digital Signal Processor (DSP) that performs all
  the functions
• Better sound cards employ additional processors
  to add surround sound and digital effects

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The Old Days of Sound Cards

• Early sound cards depended on IRQ5 and I/O
  address 0220h to function
• As newer sound cards emerged they took other
  resources, but kept IRQ5 and 0220h for Legacy
  compatibility

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Sound Cards and DMA

• Sound cards are one of the devices that require a
  DMA channel
• If a sound card is installed before or after a
  parallel port is configured to use ACP (see the
  chapter on printers), it may not work, even
  though all else looks good