Lesson #8 Optical Storage Media

Optical Storage Media Offers high density storage at low cost. CD DVD BD

History of Optical Storage Media 1982: CD (Philips/Sony) 1983: CD-ROM 1986: CD-I (Interactive) – carries compression/decompression algorithms 1988: CD-ROM/XA (Microsoft) – optimized for multiple media. 1995: CD-RW (Read/Write). 1997: DVD 2006: Blu-Ray Disk (BD)

Basic Technology In optical storage media, information is represented by using the intensity of laser light reflected during reading. Laser beam has wave length of 780 nanometers and can be focused to a resolution of 1 micrometer. In a polycarbonate substrate layer, there are depressions, called pits, corresponding to the data to be encoded. Area between the pits are called lands.

Basic CD Technology

Basic CD Technology Substrate layer is smooth and coated with a thin reflective layer. Pits have a depth of 0.12 micrometers from the substrate surface. Laser hitting pits are reflected with weaker intensity. In contrast to magnetic disks, all data is placed on one track (spiral) for continuous playback.

Basic CD Technology

Compact Disc Digital Audio CD s have a diameter of 12 cm and are played at a constant linear velocity. A CD track has approximately 20000 windings (by comparison, a vinyl LP has approximately 850). The length of a pit is always a multiple of 0.3 micrometer. A change from pit to land and from land to pit represents a binary “1”. No change means “0”.

Audio CD Technology

Audio CD Technology

Audio CD Technology

Eight-to-Fourteen Modulation Because the laser may not be precise enough to detect land to pits changes, two lands and two pits must always follow each other. To synchronize speed, there can be no more than ten 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

Eight-to-Fourteen Modulation

DVD Technology DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing for 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.

DVD Capacity

Dual Layer DVD Dual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.54 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. Along with this, DVD-DL's have slower write speeds as compared to ordinary DVD's and when played on a DVD player, a slight transition can be seen between the layers. These DVDs are also known as DVD-9, compared to the single-layer DVD-5.

Dual-Layer DVD A dual-layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds.

Dual-Layer DVD There are two modes for dual-layer orientation. With Parallel Track Path (PTP), used on DVD-ROM, both layers start at the inside and end at the outside with the lead-out. With Opposite Track Path (OTP), used on many DVD Video discs, the lower layer starts at the inside and the upper layer starts at the outside where the other layer ends; they share one lead-in and one lead-out. However, some DVD Video discs also use a parallel track, such as those authored episodically, as in a disc with several separate episodes of a TV series; where the layer change is in-between titles.

DVD Video Most consumer DVD Video discs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720/704×480 (NTSC) or 720/704×576 (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 format with monaural to 6.1-channel "Surround Sound" presentation, and/or MPEG-1 Layer 2 and/or LPCM Stereophonic. The DVD format remains the preferred one for the release of older television programs and films.

Blu-Ray Disc BD are used for storing high-definition video, PlayStation 3 video games, and other data, with up to 25 GB per single layered, and 50 GB per dual layered disc. Although these numbers represent the standard storage for Blu-Ray drives, the specification is open-ended. The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nm red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost ten times more data storage than a DVD.

Blu-Ray Disc BD are used for storing high-definition video, PlayStation 3 video games, and other data, with up to 25 GB per single layered, and 50 GB per dual layered disc. Although these numbers represent the standard storage for Blu-Ray drives, the specification is open-ended. The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nm red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost ten times more data storage than a DVD.

Blu-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, which allows backwards compatibility. MPEG-4 AVC was developed by MPEG, Sony, and VCEG. VC-1 is a codec that was mainly developed by Microsoft. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high- definition content on a single-layer (25 GB) BD- ROM. The more-advanced video codecs (VC-1 and MPEG-4 AVC) typically achieve a video run time twice that of MPEG-2, with comparable quality.

End of lesson