Chapter 6: Storage

1
Chapter 6 Storage
2
Optical media

• well accepted because
• high storage capacity
• CDROM650MB
• DVD 4.7GB 17GB
• HD-DVD 15GB per side
• Blu-ray (BD) 25GB per side
• random access to data
• life span of more than 30 years (if handled
  properly)
• portable

3
Optical media

• Videodisks developed by Philips has been
  commercially available since 1978.
• Compact disk technology for digital audio (CD-DA)
  came out in early 1980s. The use of optical disks
  for digital data storage came with the
  introduction and improvement of CD-ROM during the
  1980s.

4
Optical disk technology

• Optical storage media use the intensity of
  reflected laser light as an information source.

5
Optical disk technology

• An optical disk consists of 3 layers
• Protective layer (a very thin layer on the label
  side)
• Reflective layer (aluminum coating)
• Substrate layer (transparent)

• In the factory, depressions are cut on the disk
  surface, forming lands and pits (0.12?m
  different in heights).

6
Optical disk technology

• Laser reflected from the lands and pits give
  different readings.
• Do you know
• that data are read from the disk inside-out?
• that the spiral track is about 3.5 miles long?
• that you should never write on the label side?
• that a CD should be cleaned radially?

7
Advantages of optical media

• High density (for a portable device). Distance
  between tracks is 1.6?m (CD), each track is 0.6?m
  wide.
• Long life and low wearing. Laser source in head
  can be positioned at 1 mm from disk surface. Disk
  head does not have to be as close to the surface
  as with magnetic disks. This reduces friction and
  increases life span.

8
Digital optical disks

• Audio CD was developed by Philips and Sony in
  1982.
• Basic technology extended to 650 MB CD-ROM in
  1985.
• At single speed, data rate is 150KBps.
• CD-ROM/XA announced in 1986 to support
  applications of text, images, audio and FSFM
  video.
• Recordable media include CD-R, CD-RW, MO (magneto
  optical), and DVD.
• Latest development HD-DVD, Blu-ray.

10242 bytes
1024 bytes
Full-screen full-motion
9
CD-DA(Compact Disk Digital Audio)

• 1982 by Philips and Sony
• 12cm diameter, 1.2 mm thick optical disk,
  stores/plays in CLV (constant linear velocity).
  Spiral tracks of about 20,000 windings in total.
• CLV The same amount of track length goes through
  the disk head in the same amount of time.
• Data are recorded such that pit-to-land and
  land-to-pit transitions are coding 1s. 0s are
  coded as no transition.
• Redundancy added to break up consecutive 1s and
  0s.

10
CD-DA

• Data rate (single speed) 44.1KHz sampling,
  16-bit quantization, stereo, 172.27 KBps
• Capacity 747MB of audio data, 74 min
  high-quality sound
• Capability of random access to tracks and index
  points.
• 99 tracks per disc

11
8 to 14 modulation (EFM)

• Pits and lands may not follow too closely one
  after another on a CD-DA.
• Rule 1 between any 2 1s, there are at least 2
  0s.

1
1
1
1
0
0
12
8 to 14 modulation (EFM)

• For synchronization, pit or land sequences are
  not allowed to be too long.
• Rule 2 at most 10 0s can follow one after
  another.

1
1
0
0
0
0
0
0
0
0
0
0
0
eleven 0s
13
8 to 14 modulation (EFM)

• Solution Map every 8 bits of user data into a
  14-bit pattern (called channel bits) that
  satisfies the 2 rules.
• Among the 214 patterns, 267 of them are valid.
• Also, between consecutive 14-bit sequences, 3
  merging bits are added to enforce the rules.

14
8 to 14 modulation (Example)
15
Low level data encoding

• Thus, an eight-bit byte of actual data is encoded
  into a total of 17 channel bits (i.e., pits and
  lands).
• For synchronization and error correction, every
  24 bytes of audio data is packaged into a frame
• sync pattern (24 3 bits)
• control byte (17 bits)
• 12 data bytes (12 17 bits)
• 4 error correction bytes (4 17 bits)
• 12 data bytes (12 17 bits)
• 4 error correction bytes (4 17 bits)
• Total 588 channel bits for 192 actual data bits.

numbers in brackets are channel bits
First-level error correction
16
First level error correction

• Recall that each frame contains 24 data bytes and
  8 error correction bytes.
• The first 4 correction bytes cover the frames
  data. The other 4 correction bytes cover data
  over 7 frames.
• When a frame is read, the first 4 correction
  bytes are checked. If not ok, the decoder decodes
  the data bytes after subsequent correction codes
  are read.
• 7 frames 7.7 mm track length. Try cover your CD
  with a small piece of paper and see if it still
  works.

7.7mm
17
Interleaved coding

• An audio CD records samples from an audio wave.
  Successive sample values are closely related.
• A scratch on a CD may wipe out a continuous
  segment of data.
• With interleaving, the samples are dispersed
• 1 2 3 4 5 6 7 6 5 4 3 4 5 4 5 4 5 6 7 8 9 8 7 6
  7
• 1 6 3 4 9 2 7 4 5 8 3 6 5 6 7 4 5 4 7 6 5 4 5 8 7

Audiodata
on a CD
18
Interleaved coding

• Suppose a burst error occurs destroying 4 samples
• 1 2 3 4 5 6 7 6 5 4 3 4 5 4 5 4 5 6 7 8 9 8 7 6
  7
• 1 6 3 4 9 2 7 4 5 8 3 6 5 6 7 4 5 4 7 6 5 4 5 8 7
• Interpolation to restore (approximately) the
  sample values
• 1 2 3 4 5 6 6 6 5 4 3 4 5 4 5 4 5 6 7 8 8 8 7 6 7

19
CD-ROM(Compact Disk Read Only)

• 1985 by Philips and Sony.
• Tracks are divided into audio and data types.
  Disks containing both types are called Mixed Mode
  Disks.
• It operates in 2 modes
• Mode 1 for computer data
• Mode 2 for media data

20
CD-ROM(Compact Disk Read Only)

• Mode 1
• Mode 1 achieves a better (lower) error rate by
  using a second level of error correction.
• Random access to sub-track units called blocks
  (2352 bytes). (For CD-DA, random access is on
  track level only.)
• Each block has the address of minsecblock.
  (There are 75 blocks / second). The address is
  specified in the Header field.

21
CD-ROM

• Mode 1 for computer data. A capacity of 333,000
  blocks to be played in 74 min, i.e., 650MB
  storage with a data rate of 150KBps.
• Note that user data is protected by 4 bytes of
  error-detecting code and 276 bytes of
  error-correcting code. These are called the 2nd
  level of error correction.

Note each 24 of the 2352 bytes are represented
physically on the disc as a frame (i.e., 588
channel bits). Each block is thus represented by
98 frames.
22
CD-ROM

• Mode 2
• Mode 2 holds data of any media.
• Additional error correction not crucial, so not
  used.
• Disk has a capacity of 740MB and a data rate of
  171KBps.

23
CD-ROM

• CD-ROM is a very economical medium for
  publication and distribution.
• Limitations of CD-ROM
• Relatively slow random accesses.
• Optical disk heads are heavier than magnetic
  heads. More inertia takes a longer seek time for
  head movements.
• Due to CLV, a disc has to be accelerated or
  decelerated when the head moves from a track to
  another.
• Continuous media stored sequentially in CD-ROM
  tracks. Although important for multimedia
  applications, simultaneous playback of audio and
  other data is not possible.

24
CD-ROM/XA(Extended Architecture)

• 1989, established by Microsoft, Philips and Sony.
• Goal concurrent output of several media. Within
  1 track, blocks of different media can be stored.
  It allows interleaved storage and retrieval of
  multimedia data.
• A sub-header is added to each block to describe
  the block.
• CD-ROM/XA uses CD-ROM mode 2 to define actual
  blocks. Two forms

25
CD-ROM/XA

• Form 1 provides more error detection/correction
  at the expense of redundancy. 2048 bytes (of
  2352) are for user data.
• Form 2 allows 13 more storage for user data,
  but at the expense of error correction.

26
CD-R(Compact Disk Recordable)

• CD-R allows tracks to be recorded once.
• 4 layers protective, reflective, dye, and
  substrate.

24K
Traditional CD-ROM
CD-R Media
Lacquer
Lacquer
Aluminum
Gold
Dont leave out in sunlight
Dye
Polycarbonate
Polycarbonate
Molded by a stamper
Burned by high power laser beam
27
CD-R

• Land and pit reflections realized by irreversible
  thermal effect (above 250C) on the dye.
• Playable on CD players.

28
CD-R

• Recording sessions
• A CD has 3 areas lead-in, actual data, lead-out.
• Lead-in includes the table of contents
  directory, indices to individual tracks.
• Data area includes all tracks where actual data
  is stored.
• Lead-out marks the end of the data area.

29
CD-R

• Recording sessions
• Multiple sessions of lead-in, data, lead-out can
  be written separately over time.
• During 1 write activity, all data for a session
  are written with their table of contents, after
  which the session can be read by a CDROM drive.

30
CD-MO(Compact Disk Magneto Optical)

• Specification published by Philips and Sony in
  1991.
• Working principle is different from other CD
  technologies (incompatible with other CD
  formats.)
• Based on the polarization of light by magnetic
  field.
• Disk surface is light reflecting magnetic
  substrate.
• During writing, surface is heated to above 150C,
  and a magnetic field polarizes individual
  dipoles.
• During reading, surface is irradiated with a
  laser beam, polarization of laser light changed
  according to the magnetization.

31
CD-RW

• An alloy is used in CD-RW that can take on two
  states
• crystalline reflects light well
• amorphous doesnt reflect light well
• To change the alloy into the crystalline state
  or the amorphous state, two laser beams of
  different power are used
• Write power amorphous state
• Erase power crystalline state
• Read power no state change, used to pick up
  the readings from the disk

32
Sony MiniDisk

• A small MO disk with a data capacity of about 1/5
  of a CD.
• An MD can record about the same length of music
  as a CD since the audio is compressed.
• The compression technique used is called ATRAC
  (Adaptive Transform Acoustic Coding). Typical
  compression ratio is 51.
• Like MP3, ATRAC uses psychoacoustics.

33
Digital Versatile Disk (DVD)

• also called Digital Video Disk.
• capacity 4.7 to 17 billion bytes (25 CDs)
• digital video can be stored and distributed
  cheaper than tape also it allows interactivity
• can be used to store up to 133 minutes (8-9 hrs
  for high capacity DVDs) of studio quality video
  and multi-channel surround-sound audio, or 30
  hours of CD-quality audio

34
DVD

• DVD achieves a greater capacity by
• reducing the minimum pit length from 0.834 micron
  (CD) to 0.4 micron (DVD)
• reducing the inter-track space from 1.6 micron
  (CD) to 0.74 micron (DVD)

Track pitch
35
DVD

• To read the condensed pits, DVD uses a laser of a
  shorter wavelength (635-650 nm for CD it is 780
  nm).
• Reducing the pit size and track distance
  increases the discs capacity to 4.7GB.
• Dual layering. A semi-reflective layer on top of
  a fully reflective layer ? 8.5GB total.
• Double side. Two substrates bonded back-to-back.
  Each side could have one layer or two layers ?
  capacity ranges from 9.4GB to 17GB.

36
DVD
4.7GB
8.5GB
17GB
37
DVD

• Other factors that improve the storage capacity
• 8-16 modulation instead of 8-14 3 merge bits
• slightly larger usable surface area
• more efficient error coding

38
DVD

• Other features
• Error correction is about 10 times better than
  that of CD.
• Some DVDs are recorded using opposite track path
  (i.e., one spiral layer starts from the center,
  followed by another spiral layer that starts from
  the rim towards the center). OTP reduces the seek
  time when the player switch layer during video
  playback.

39
HD-DVD and Blu-ray (BD)

• Next generation optical disks
• Two competing camps
• Both use blue laser (405nm). Shorter wavelength ?
  smaller pits ? more storage density.

40
HD-DVD

• Supported by DVD-forum with more than 230
  members
• Toshiba, Sanyo, NEC, Paramount Pictures,
  Universal Pictures, New Line Cinema and the
  Warner Bros Studios.
• Capacity 15GB (single-sided), 30GB
  (double-sided)
• Disk structure very similar to DVD ? small
  conversion cost from DVD production line to
  HD-DVD line ? cheaper manufacturing cost at the
  moment.

41
BD

• Supported by Blu-ray Disc Association (BDA) with
  about 100 members
• DELL, HP, Hitachi, LG-Electronics, Mitsubishi
  Electric, Panasonic, Pioneer, Philips, Samsung,
  Sharp, Sony, TDK, Thomson, 20th Century Fox, Walt
  Disney, Texas Instruments, Sun Microsystems, the
  game giants Electronic Arts, and Vivendi
  Universal Games.
• Capacity 25GB (single-sided), 50GB
  (double-sided)
• For a higher capacity, BD uses a thin substrate
  layer (0.1mm) ? more expensive to convert exiting
  DVD production line to make BD ? more expensive.
  Also, the thin layer requires a hard coating to
  protect the disc from damages.
• With a higher data density, BD offers a higher
  transfer rate than HD-DVD.