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8. Optical Storage Media - Copyright Denis Hamelin - Ryerson University

Lesso n #8Op tic al Stor ag e Med ia

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Optic al Sto rag e Med ia

Offers high density storage at low cost.

CD

DVDBD

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Histo ry o f Opt ica l Sto rageMedia

1982: CD (Philips/Sony)

1983: CD-ROM

1986: CD-I (Interactive) carriescompression/decompression algorithms

1988: CD-ROM/XA (Microsoft) optimized formultiple media.

1995: CD-RW (Read/Write).

1997: DVD

2006: Blu-Ray Disk (BD)

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4/238. Optical Storage Media - Copyright Denis Hamelin - Ryerson University

B as ic Tech no logy

In optical storage media, information isrepresented by using the intensity of laser lightreflected during reading.

Laser beam has wave length of 780 nanometersand can be focused to a resolution of 1micrometer.

In a polycarbonate substrate layer, there aredepressions, called pits, corresponding to the datato be encoded. Area between the pits are calledlands .

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B asic CD Tech no logy

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Substrate layer is smooth and coated with a thinreflective layer.

Pits have a depth of 0.12 micrometers from thesubstrate surface.

Laser hitting pits are reflected with weakerintensity.

In contrast to magnetic disks, all data is placed onone track (spiral) for continuous playback.

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Com pact Disc Digi tal A ud io

CD s have a diameter of 12 cm and areplayed at a constant linear velocity.

A CD track has approximately 20000 windings(by comparison, a vinyl LP has approximately850).

The length of a pit is always a multiple of 0.3

micrometer. A change from pit to land and from land to pitrepresents a binary 1. No change means 0.

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A ud io CD Tech no logy

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Eig h t-to-Fo u r teen Mo d u lat ion

Because the laser may not be precise enough todetect land to pits changes, two lands and two pitsmust always follow each other.

To synchronize speed, there can be no more thanten consecutive zeros as channel bits.

So real bits do not always follow the pits and lands.

To do that the 8-to-14 modulation must be applied(from a table).

00000000 becomes 01001000100000

00000001 becomes 10000100000000

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Eig h t-to-Fo u r teen Mo d u lat ion

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DVD Tech no log y

DVD uses 650 nm wavelength laser diode light asopposed to 780 nm for CD. This permits a smaller pitto be etched on the media surface compared to CDs(0.74 m for DVD versus 1.6 m for CD), allowingfor a DVD's increased storage capacity.

Each DVD sector contains 2,418 bytes of data,2,048 bytes of which are user data. There is a small

difference in storage space between + and -(hyphen) formats.

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DVD Cap ac ity

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Dual Layer DVD

Dual-layer recording (sometimes also known asdouble-layer recording) allows DVD-R and DVD+Rdiscs to store significantly more data up to 8.54gigabytes per disc, compared with 4.7 gigabytes forsingle-layer discs. Along with this, DVD-DL's haveslower write speeds as compared to ordinary DVD'sand when played on a DVD player, a slight transitioncan be seen between the layers.

These DVDs are also known as DVD-9, compared tothe single-layer DVD-5.

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Du al-L ayer DVD

A dual-layer disc differs from its usual DVDcounterpart by employing a second physical layerwithin the disc itself. The drive with dual-layercapability accesses the second layer by shining thelaser through the first semitransparent layer.

In some DVD players, the layer change can exhibit anoticeable pause, up to several seconds.

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Du al-L ayer DVD

There are two modes for dual-layer orientation. WithParallel Track Path (PTP), used on DVD-ROM, bothlayers start at the inside and end at the outside withthe lead-out. With Opposite Track Path (OTP), used

on many DVD Video discs, the lower layer starts atthe inside and the upper layer starts at the outsidewhere the other layer ends; they share one lead-inand one lead-out. However, some DVD Video discsalso use a parallel track, such as those authoredepisodically, as in a disc with several separateepisodes of a TV series; where the layer change isin-between titles.

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DVD Video

Most consumer DVD Video discs use either 4:3 oranamorphic 16:9 aspect ratio MPEG-2 video, storedat a resolution of 720/704 480 (NTSC) or720/704 576 (PAL) at 29.97, 25, or 23.976 FPS.

Audio is commonly stored using the Dolby Digital(AC-3) or Digital Theater System (DTS) formats,ranging from 16-bits/48 kHz to 24-bits/96 kHz formatwith monaural to 6.1-channel "Surround Sound"presentation, and/or MPEG-1 Layer 2 and/or LPCMStereophonic.

The DVD format remains the preferred one for therelease of older television programs and films.

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B lu-Ray Disc

BD are used for storing high-definition video,PlayStation 3 video games, and other data, with upto 25 GB per single layered, and 50 GB per duallayered disc. Although these numbers represent the

standard storage for Blu-Ray drives, thespecification is open-ended.

The name Blu-ray Disc derives from the blue-violetlaser used to read the disc. While a standard DVD

uses a 650 nm red laser, Blu-ray uses a shorterwavelength, a 405 nm blue-violet laser, and allowsfor almost ten times more data storage than a DVD.

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B lu-Ray Disc

BD are used for storing high-definition video,PlayStation 3 video games, and other data, with upto 25 GB per single layered, and 50 GB per duallayered disc. Although these numbers represent the

standard storage for Blu-Ray drives, thespecification is open-ended.

The name Blu-ray Disc derives from the blue-violetlaser used to read the disc. While a standard DVD

uses a 650 nm red laser, Blu-ray uses a shorterwavelength, a 405 nm blue-violet laser, and allowsfor almost ten times more data storage than a DVD.

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B lu-Ray Video

For video, all players are required to support MPEG-2 Part 2, H.264/MPEG-4 AVC, and SMPTE VC-1.MPEG-2 is the codec used on regular DVDs, whichallows backwards compatibility. MPEG-4 AVC was

developed by MPEG, Sony, and VCEG. VC-1 is acodec that was mainly developed by Microsoft.

Discs encoded in MPEG-2 video typically limitcontent producers to around two hours of high-

definition content on a single-layer (25 GB) BD-ROM. The more-advanced video codecs (VC-1 andMPEG-4 AVC) typically achieve a video run timetwice that of MPEG-2, with comparable quality.

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En d o f les s o n

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