DVD Demystified

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Glossary
also used in Canada, Japan, and other parts of the world. NTSC is facetiously
referred to as meaning never the same color because of the system’s
difficulty in maintaining color consistency.
NTSC-4.43 A variation of NTSC in which a 525/59.94 signal is encoded
using the PAL subcarrier frequency and chroma modulation. Also
called 60-Hz PAL.
numerical aperture (NA) A unitless measure of the capability of a
lens to gather and focus light. NA � n sin 1, where 1 is the angle of the
light as it narrows to the focal point. A numerical aperture of 1 implies
no change in parallel light beams. The higher the number, the greater
the focusing power and the smaller the spot.
OEM Original equipment manufacturer. A computer maker.
operating system The primary software in a computer, containing general
instructions for managing applications, communications,
input/output, memory, and other low-level tasks. DOS, Windows, Mac
OS, and Unix are examples of operating systems.
opposite path See OTP.
Orange Book The document begun in 1990 that specifies the format of
recordable CD. Its three parts define magneto-optical erasable (MO)
and write-once (WO) discs, dye-sublimation write-once (CD-R) discs,
and phase-change rewritable (CD-RW) discs. Orange Book also added
multisession capabilities to the CD-ROM XA format.
OS Operating system.
OSTA Optical Storage Technology Association. Refer to Appendix C,
“References and Information Sources.”
OTP Opposite track path. A variation of DVD dual-layer disc layout
where readout begins at the center of the disc on the first layer, travels
to the outer edge of the disc, then switches to the second layer, and
travels back toward the center. Designed for long, continuous-play programs.
Also called RSDL. Contrast this with PTP.
out of band In a place not normally accessible.
overscan The area at the edges of a television tube that is covered to
hide possible video distortion. Overscan typically covers about four or
five percent of the picture.
pack A group of MPEG packets in a DVD-Video program stream. Each
DVD sector (2,048 bytes) contains one pack.
packet A low-level unit of DVD-Video (MPEG) data storage containing
contiguous bytes of data belonging to a single elementary stream such
as video, audio, control, and so forth. Packets are grouped into packs.
packetized elementary stream (PES) The low-level stream of MPEG
packets containing an elementary stream, such as audio or video.