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Glossary of EMedia Technology
Leo F. Pozo
To move quickly through this glossary, click on the first letter of the entry you are searching for: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, Y. To return to the beginning of this glossary, click on the letter that titles the section you are in.
A
- A-D Conversion
- Analog to digital conversion, also known as modulation,
involves special chips to convert analog signals to digital
strings, or vice-versa. A-D conversion is necessary to send
computer data through telephone lines, to produce digital audio,
to have computerized telecommunications, to display data on
analog displays, and so on.
See, Modem
- A-Time
- Absolute Time is used to access sectors of data from the CD-
ROM, identifying or addressing them from the beginning of the
disc, using the drive's internal clock (min:sec:sector). It
allows access of random amounts of data, such as video and audio
segments, especially if the disc will include more than 98
individual audio segments. In Mixed-Mode discs, since only 98
tracks of CD-DA are allowed, track access is not workable. A-
Time access involves mapping the audio portions in the CD-ROM
(start and stop of each) using time addresses (Min-Sec-Sector),
mapped relative to the beginning of the disc. This requires
special care in determining the 'offset'--the amount of time used
by all the components of Track 1 (pregap, post gap, application,
etc.). Track relative time, on the other hand, involves mapping
the times relative to the beginning of its track--which is a much
easier option, and widely used in Mixed-Mode discs.
See, Track Access
- Access Time
- Amount of time it takes a CD-ROM drive to find and display
the requested information. Although specified widely, access
times must be used with care because there is no measuring
standard. It is generally regarded to include radial positioning
time (the head moves to the appropriate track), plus settling
time (stops vibration), plus latency (wait for beginning of block
with the wanted data)--all which take much more time than the
final read and display step. The faster hard disk drives claim
access speeds of 12 milliseconds or even lower, while the faster
CD-ROM drives claim access speeds about 150 milliseconds.
- Adapter Cards
- In computers, adapter cards (a.k.a. controller cards,
expansion cards, interface cards, etc.) are small panels
installed or plugged into slots of the main data bus, or bus
extensions such as Local Bus. They are also necessary for
networking computers. The cards 'adapt' the flow of data and
instructions between the CPU and the device (peripheral), thus
enhancing the computer's capabilities (memory expansion, fax-
modem, advanced graphics, sound, I/O expansion, processor
upgrades, etc.).
- ADPCM
- Adaptive Differential Pulse Code Modulation is an audio
encoding procedure (often referred to as compression algorithm)
that takes about half the space of standard PCM, and involves
different sampling rates and bits per sample, algorithms and
chips to produce up to 20 hours of Level C, monaural audio in one
CD. 'Differential' (often called 'Delta') refers to the way the
algorithms determine and record only the differences between one
signal and the next, using 4-bit numbers--thus reducing the total
length of code. It is implemented with interleaving in CD-I and
CD-ROM-XA applications.
See, Modulation
- Analog Signal
- A continuous signal that reflects the variation in the
phenomenon being measured or represented, such as voice,
temperature, pressure, intensity of light, electrical flows, etc.
To be used in computers, analog signals, such as those in
communications, must first be modulated into digital code.
See, Modem
- Application
- In computer circles, it is a complete package of software and
data designed to work in a particular computing platform. Main
applications today involve wordprocessor, spreadsheet, database,
desktop publishing (DTP), reference works, games, graphics,
multimedia products, etc.
- Artwork
- See, Packaging
- ASCII
- The American Standard Code for Interchange of Information,
better known as the ASCII ('askey') character set, is the binary,
7-bit, 128-character set implemented as the standard in
communications, and in mini and microcomputers. Because data is
transferred as bytes, ASCII codes are added an eight bit
(generally a 1-bit) to make up the standard eight-bit byte. This
eighth bit is generally used as a parity bit.
See, EBCDIC
- ASPI
- Advanced SCSI Programming Interface is, essentially, a driver
that helps the operating system deal with SCSI devices, such as
CD-Recordable drives, by configuring it appropriately (dealing
with the bus, ports, DMA channels, interrupts, other SCSI
devices, etc.). ASPI is loaded by the CONFIG.SYS, and there are
versions for various bus architectures.
- Audio
- Until recently, audio signals have always been recorded and
played back as analog signals. In computer circles, audio refers
to files of digital (binary) codes that are produced by
converting analog signals to digital audio. The quality of
digital audio depends on the sampling rate and the sample size.
See, CD-Digital Audio
- Audio Standard
- See, CD-Digital Audio
Red Book
Standards
- Average Access Time
- Average time, in milliseconds, it takes for a CD-ROM drive to
complete a request to read task--the word to note here is
'average.' Some manufacturers specify their 1/3 stroke access
time, and others specify random access time (also referred to as
random seek time), or a combination of them--reason why using
access times for comparisons should not be considered reliable
and sufficient.
B
- Bandwidth
- Originally a range of frequencies, in current computer
circles it describes the capacity or amount of traffic (data,
voice, video, etc) per unit of time. Mbits/second prevails in
computer communications, while MBytes/second are used in most
other computer applications. Some of the new microcomputer buses
and local buses have bandwidths of up to 132 MBytes/sec. The
first CD-ROM drives had a transfer rate of 150 Kbytes/second.
See, SCSI
Transfer Rate
- Binary code
- Computers are based on binary code; binary digits (bits), 0s
and 1s that form bytes and files. Information is stored in binary
files, in specific formats. Optical devices, such as CD-ROM,
involve physical 'pits' and 'lands' on the coded track of the
disc. But, in the end, they are decoded into 1s and 0s of files
that can be used by the computer.
- Birefringence
- In CDs and other optical discs, it means double refractive
ability. It is caused mainly by improper cooling of the
substrate during the injection-molding process. In optical
applications, however, birefringence is obviously unwanted, since
it interferes with the read function. Users, however, can not
determine that it is birefringence that is causing read errors or
poor performance of their CD-ROM applications--it is detected by
special equipment and tests.
- Bit
- A compressed form of 'binary digit.' Therefore, a bit can be
a 1 or a 0. A standard byte has eight bits (256 possibilities).
Bits are used mostly when dealing with bandwidth rates
(bits/sec), graphics resolutions, and related topics. Bytes are
used when talking about data and files in general.
See, Byte
- BLER
- Block Error Rates indicate the number of blocks that contain
erroneous bytes (error bursts) during a read from the CD-ROM.
BLERs also serve to gage effectiveness of mastering, replication,
and CD-R encoding processes. Analysis of BLERs require
understanding the basic Reed-Solomon error correction code, and
the Cross-Interleaved Reed Solomon Code (CIRC)--which are basic
for the first two layers of error detection and correction in
CDs. An average BLER of less than 220 is considered within the
specifications.
See, SIGCAT
- Block
- Unlike the blocks used in regular magnetic storage devices,
in ISO 9660 optical discs, logical blocks are subdivisions of the
sectors in the track. But, in most applications, the logical
block is considered to be the same size as the user data area of
the sector. This option has led to the common notion that, in
CD-ROM, blocks and sectors are the same thing--which is obviously
not true for all cases.
See, Frame
Sector Structure
- Block structure
- See, Sector Structure
- Blue Book
- This draft of the technical specifications of a High Density
CD (HDCD), proposed by the Optical Disc Corporation (ODC), was
submitted to the International Electrotechnical Commission (IEC)
for adoption as a standard. It mentions the use of a new higher
definition red laser to achieve a capacity of up to 3.3 gigabytes
of user data in a CD. It apparently also claims that, using MPEG
compression and a transfer rate of 3.3 Mbits/sec, the HDCD will
be able to store a 135-minute full-length movie in one HDCD.
See, DVD
- Blue Laser
- The development of a blue-light emitting diode (based on
gallium nitride), in l993, in Japan, has opened the way for the
production of a blue laser--which would essentially make possible
the production of multi-Gigabyte optical discs. Some analysts
observe that the technology is being tested in industrial and
research applications, and expect that it will be implemented in
the high stakes optical disc arena--by about 1998.
- Boolean Search
- One of the various logical constructs (Boolean Operator,
Logic, Modifier, etc.) named after George Boole (1815-65), a
British mathematician who developed a system of algebraic logic
that has been applied beneficially in various areas, including
computer logic circuits and software applications. Most text
search and retrieve software use the Boolean operators And, Or,
Not, ButNot, etc. Boolean logic for database or numerical fields
includes operators such as 'Less than,' 'More than,' 'Equal or
More than,' 'Equal or Less than,' and so forth. With the advent
of powerful processors and affordable memory, there is interest
in other logical systems that produce faster text searches, some
quite sophisticated indeed, especially in large and very large
textbases. Boolean searching, however, remains predominant.
- Bootable CD
- Some operating systems recognize and can use an ISO file
structure, and therefore the CD can be configured with a boot
record descriptor and operating system files (boot file), so the
PC can boot from it--as some CDTV systems do. But, the Microsoft
CD-ROM Extensions do not recognize the boot record descriptor in
the CD, so MS-DOS PCs can not boot from it. As an alternative,
in 1995, IBM and Phoenix Technologies announced an open Bootable
CD-ROM format specification that would allow placing bootable
images of floppies or hard disks on the CD-ROM, and a bootable
CD-ROM BIOS in the system. To boot-up, the CD-ROM BIOS allows
the system to read the preconfigured 'boot image' and proceed
with the rest of the configuration. It was expected that
applications with special configurations, games, multimedia
applications and others will use the 'bootable CD' option, but
there is no clear evidence of that yet.
- Buffer
- A usually small amount memory, directly available to the CPU,
which holds momentarily either instructions or other information
for it--not to be confused with memory cache. Buffers are used
to overcome factors that affect direct access of instructions or
data to the CPU; such as speed differences, interface delays,
and other variations between a device and the CPU.
- Bundling
- The practice of selling hardware or software, with additional
items that, supposedly, do not add to the total price.
Initially, minor software products were bundled with PCs and some
peripherals. Recently, DOS, Windows, Modems, speaker sets, and
especially CD-ROMs and Multimedia applications of various types
are bundled with hardware and major software packages. This
practice, however, has helped the growth of CD-ROM.
- Bus
- In computers, a bus is the main or continuous channel of
electrical connection between the CPU, the system memory (RAM),
and the peripheral devices.
See, ISA Bus
EISA Bus
MCA Bus
PCI Local Bus
PCMCIA
HPSB
- Byte
- Bytes are strings of bits, operated upon as a unit. Until
recently, PCs were designed to use 8-bit bytes. The 128
characters of the ASCII character set are represented by 8-bit
bytes, (seven plus a parity bit--thus only 128 characters). Bytes
are also basic for the Hex and Octal notation used in computer
programming. PCs measure file lengths and storage in bytes.
Current PCs are implementing 32-bit buses, with 16 and 32-bit
processors (which means they can handle data and instructions in
strings of those lengths). For encoding CD-ROM discs, the
magnetic 8-bit byte is modulated to the 14-bit optical byte.
See, Bit
EFM
C
- Caddy
- A 'caddy' is a special plastic case that holds and protects
the CD during operation--especially when the drive is mounted on
its side. Caddies are not used for shipping. For WORM and
Erasable media, they are called cartridges--probably because they
do not allow extraction of the disc itself.
See, Jewel Case
- Capacity
- In general, the term capacity refers to the capacity of a CD,
in megabytes of user data. Currently, there are CD-ROM media
that can hold 63 or 74 minutes of data (74 min. is the maximum
designed capacity). Before, because of equipment and other
considerations, CD-Audio and CD-ROM did not use the outer area of
the disc, and 60 to 63-minute discs were the rule. Today, because
current equipment can encode and drives can read the outer area
of the disc, 74-minute discs are common. The capacity of the
disc, in bytes, is the number of user bytes per block, times 75
blocks per second, times the total time recorded in the disc.
Furthermore, the total, in Megabytes, will depend on the
definition of Megabyte. Using 2(exp 20), or 1,048,576, we will
arrive to the figure of 527 MBytes for a 60 minute CD-ROM.
Obviously, this figure will be much higher for a 74-minute CD-
ROM. Moreover, with multimedia CD-ROMs, all figures of capacity
have to take into consideration the different amounts of user
data in the blocks used for audio, video, and text. It is
therefore possible to produce a 74-minute disc, Mode 2 (video,
2336 user bytes per sector), with about 778 million bytes, or
about 741 Megabytes of user data in it--and still remain within
the ISO 9660 specifications. Users must be aware, therefore, of
all these variables when dealing with disc capacities.
See, Sector Structure
Raw Capacity
- CAV/CLV
- See, Constant Angular Velocity...
- CCITT
- The International Consultative Committee for Telegraphy and
Telephony, established by the United Nations within the
International Telecommunications Union (ITU), is based in Europe,
and recommends worldwide telegraph and telephone (including fax)
transmission standards.
- CD
- The Compact Disc was developed by Philips and Sony, and was
first implemented commercially for storing digital audio data
(CD-Digital Audio). The physical specifications for the 12cm
disc, since known as CD, were issued in the now famous Red Book.
The CD is made up of a polycarbonate substrate, a thin reflective
metallic layer (the mirror-like is aluminum), and a lacquer
coating. The encoded data track is a spiral track of about 2.2
microns wide, with the pits making a central band 0.6 microns
wide. The encoded track is made up of sectors (sometimes
erroneously named blocks). Essentially, any other size of
optical disc is not a CD.
See, Red Book
Sector Structure
- CD-Audio
- See, CD-Digital Audio
- CD-Bridge Disc
- A Bridge disc is defined as a CD-ROM XA disc that includes
Mode 2 user data that can be played with a CD-I player.
Additional codes in the CD-ROM XA tracks allow the output to be
shown on a TV screen (CD-I players), and on a computer monitor
(with CD-ROM XA players). The specifications for the CD-Bridge
disc are known as the White Book.
See, CD-I Ready
Standards
White Book
- CD-Digital Audio
- Philips and Sony developed the necessary technology for
storing digital audio signals on a Compact Disc and, in 1982,
introduced the CD-Digital Audio. This new product was based on
the now famous Red Book (1981)--which specified the physical
structures for the track and sectors in the disc. CD-Digital
Audio was implemented to hold about 60 minutes of audio data, in
up to 99 tracks (songs) at a sampling rate of 44.1 KHz and a
sample size of 16 bits, to produce high quality stereo
sound--thus revolutionizing sound quality reproduction. The
success of CD-Digital Audio has been key for the growth and
success of CD-ROM and other CD implementations.
See, Standards
- CD-I
- Compact Disc-Interactive was developed by Philips and Sony,
who issued the specifications in 1986, in what is known as the
Green Book. CD-I employs the CD, with a sector structure similar
to CD-ROM-XA, and addresses issues of synchronization to
implement interleaved data, compressed audio, still frames and
full-motion video files, complying with the ISO 9660. CD-I was
advertised as the upcoming interactive multimedia platform, but
current CD-I products aim mainly towards business and education
multimedia interactive applications. A mayor drawback was that
CD-I uses proprietary hardware, operating system (OS9), and data
compression solutions--including MPEG-1. The keyboard-less CD-I
drives range from the basic player to the professional set, and
can display to NTSC and PAL monitors. CD-I players can play CD-
Audio and Bridge discs (Kodak Photo CDs, and Video CD) compliant
with the White Book. PCs, with a special add-on board, can read
CD-I discs.
See, Green Book
Standards
- CD-I Ready
- A CD-I Ready disc is defined as a CD-Audio disc that includes
a CD-I application, and can be played with a modified CD-I
player. It involves extending the pre-gap space of CD-Audio, and
including in it data that only the CD-I player can recognize and
use. This additional functionality allows CD-I to present
additional information about its contents.
See, CD-Bridge Disc
Standards
- CD-Recordable
- CD-Recordable technology allows production of CD-ROMs on the
desktop ('one-offs'). It requires a CD-R recorder, appropriate
software, a PC, and appropriate media. The reduction of prices
for this hardware and software, and their ease of use, have
helped the growth of CD-ROM production in-house. CD-Recordable
involves a special CD, the 'one-off' blank, very different from
the mass-reproduced or 'hot-pressed' CDs. It is sold pregrooved,
in 63 or 74 minute capacities, and it involves a layered
structure--with a sensitive chemical recording layer, almost
always with a gold reflective layer, and ready for a CD-
Recordable drive. Once recorded, the CD-Recordable discs (one-
offs) perform in the same way as the mass-reproduced CDs.
See, One-off Discs
- CD-RDx
- The CD-ROM Read-Only Data Exchange Standard, developed by the
CIA, Intelligence Community Staff, aimed to achieve "...system
and software interoperability for CD-ROMs," which was further
explained as the "...ability to publish a single integrated
collection of data and indexes on a CD-ROM disc and make it
accessible on any ISO 9660-compatible computer system." A final
draft circulated in early l993.
- CD-ROM
- The Compact Disc-Read Only Memory is the standard 12cm CD
formatted according to the ISO 9660. Although the physical
characteristics and track structure of a CD-ROM are the same as
that of CD-Audio, a CD-ROM is used to store computer data (text,
graphics). It also involves additional error detection and
correction--as specified in the Yellow Book. The logical volume
and file structure of CD-ROM, specified in the ISO 9660 allows it
to be used in the computer arena. Therefore, a CD with computer
data that is not structured according to the ISO 9660 is not a
standard CD-ROM.
See, ISO 9660
Standards
- CD-ROM Drives
- The growth of the industry is reflected in the types of CD-
ROM drives offered today. The original drives had a transfer
rate of 150 KBytes/second, but recent drives offer double,
quadruple and even higher transfer rates--and are known as 2X,
6X, and so on. Some early CD-ROM drives could not handle audio
tracks; current drives can handle audio tracks and, for
multimedia, have connections for the sound card. Some recent
drives are also XA-ready, and/or Photo-CD ready, with or without
multiple session capability. The choices available demands users
to consider carefully their true needs.
- CD-ROM Extensions
- The MS-DOS operating system (just as other operating systems)
was developed before optical technology became available for the
PC platform. Therefore, Microsoft had to add appropriate
capabilities to MS-DOS, so that the PC could acknowledge an ISO-
compliant CD-ROM as another storage device. The program,
MSCDEX.EXE, is known as CD-ROM Extensions, and is loaded by the
Autoexec.Bat. Apple has Apple Extensions for its Hierarchical
File System, and Commodore has CDFS extensions for CDTV.
See,
MSCDEX.EXE
- CD-ROM Tower
- This is a configuration of CD-ROM drives in one box, known as
a tower. CD-ROM towers are usually implemented in networks,
usually with an appropriate CD-ROM server. They work well in
busy multiuser environments because all the drives in the tower
are accessible at all times, while jukeboxes access only one disc
(or a few discs) at a time. Recently, some manufacturers have
introduced tower models with CD-Recordable units, and LAN-ready
configurations.
- CD-ROM XA
- CD-ROM Extended Architecture, developed by Sony, Philips and
Microsoft, involves extensions to the Yellow Book, and defines
two new types of sector (CD-ROM Mode 2 sectors are 'extended'
into CD-ROM XA Form 1 and Form 2 sectors). The new CD-ROM XA
sectors are used for data, graphics, video, and compressed audio,
in an interleaved scheme (CD-I structure)--making it possible to
read and display jointly text, graphics and audio files of
various sample sizes, up to 20 hours of 4-bit monaural sound.
Kodak's Photo CD for example, uses XA tracks, and it can
therefore be read by an XA drive.
See, Multi-session
- CD-Singles
- Since 1991, the 8cm music 'CD-singles' were popular in Japan.
Formatted under ISO 9660, the 8cm disc can hold up to 200 KB of
data and be played by the Sony Data Discman. Some CD-ROM-XA
applications have been ported to 8cm discs. This 8cmm disc
should not be confused with the Sony 8cm MiniDisc, which is an M-
O rewritable disc (Orange Book).
- CDTV
- Commodore Dynamic Total Vision, released in 1991, involved
CD-ROM for multimedia applications for Commodore PCs that
displayed to a TV monitor. Its particular file system (CDFS) is
set to use the ISO 9660 (Interchange Level 2) file format. But,
CDTV discs that implement Interchange Level 2 (allowing smaller
logical blocks, different filename lengths and character set
conventions) are incompatible with the IBM-compatible platform.
CDTV also is capable of booting from the CD. For various
reasons, CDTV weakened as Commodore lost market share in the US--
though they seem to be holding on in some foreign markets.
- CD-V
- Compact Disc-Video is an implementation of the CD to store
full motion video (analog, about 5-6 minutes) and CD-Audio tracks
(about 20 minutes). CD-V requires a special CD-V drive, and is
used mostly in the commercial video production arena. Because
digital video is implemented in various platforms, there are
video discs in 20cm (8in) and 30cm (12in) formats as well--but
these are not CDs. CD-V should not be confused with the upcoming
Digital Video Disc, nor with Video CD introduced by Panasonic.
See, DVD
Video CD
- CD-WO
- Compact Disc-Write Once is rather recent, but is often
confused with the older WORM (Write Once Read Many) technology.
More appropriately, CD-WO is defined by the Orange Book, Part 2
(1990). It involves the 12cm CD, with a recordable layer that can
be written to, but not erased and rewritten. Therefore, once the
tracks have been encoded, a Table of Contents is created and
placed in the appropriate place (the track's Lead-in). CD-ROM
players use that TOC to read the contents. A CD-WO Hybrid disc
involves an area where Read-Only files can be placed, and the
rest of the disc is the W-O area, which can be written to in one
or more sessions (each session creates its own Table of
Contents). Multi-session discs need multi-session capable
drives, such as the Kodak Photo CD drive and the newer
multi-session ready drives. The older WORM technology remained
mostly proprietary and uses optical media of various sizes.
See, W-O Technology
- Channel Bits
- The optical bytes, after the eight-to-fourteen modulation,
are recorded in channel bits--which produce the pits and lands on
the data track. In another context, channel bits refer to the
bits that make up each of the 98 Control Bytes included in each
sector. Those channel bits are named P, Q, R, S, T, U, V, and W,
and each of them represents a subcode channel, and include
important information for timing, types of information, tracking,
etc.
- CIRC
- Cross-Interleaved Reed-Solomon Code is used in compact discs
for the first two levels of error detection and correction. CIRC
in CD-Audio provides an integrity of one erroneous byte in a
gigabyte (two CDs). The additional and more sophisticated third
level 'layered' error detection and correction in CD-ROM claims
an integrity of one byte in 2,000 CD-ROMs.
See, Integrity
- Cladding
- Special material used to line or cover an optical fiber, to
reflect and confine the light waves to the core.
- CMP
- A joint Committee on Multimedia Technology formed by the
Interactive Multimedia Association (IMA) and the Society of
Motion Picture and Television Engineers (SMPTE) to deal with
issues about multimedia, produce technical papers, propose
standards and distribution guidelines, and promote product
interchange and interoperability in the multimedia industry.
- COLD Technology
- COLD is the industry term for Computer Output to Laser Disk.
The term COLD reflects the fact that optical disks (or laser
disks) were the archival media utilized in the early systems.
Current optical technology, however, offers CD-ROM-based archival
subsystems, RAID subsystems, various optical disc jukeboxes or
autochanger systems, and others--with an assortment of software
for their use. Most people are familiar with COM (Computer
Output to Microfiche), which is being replaced by COLD
technology. But, in the near future of the imaging industry,
COLD may be replaced by COAR (Computer Output Archival and
Retrieval) which is more representative of the current archival
and search and retrieve technologies--which will add more value
and broad accessibility to applications based on computer output.
- Compression
- The large file size of audio, graphics and video files for
CD-ROM applications forced development of hardware and software
compression-decompression procedures. While most compression
solutions are designed with specific types of files in mind
(text, audio, video, graphics, etc.), recent compression
solutions are quite sophisticated, and some even aim to compress
the entire contents of a CD-ROM before mastering and, decompress
when accessed--'on-the-fly'. The compression-decompression
markets will certainly remain active for the foreseeable future.
- Connectors
- These are the physical cables, receptacles and plugs used to
connect devices in and to a computer. Although they are
designed for specific types of connection (serial, parallel,
SCSI-1, SCSI-2, SCSI-SCA, etc.), most CD-ROM and other optical
devices use different connectors and cables--depending on the
manufacturer, operating system, and even model.
- Constant Angular Velocity (CAV) and Constant
Linear Velocity (CLV)
- Magnetic and optical storage drives can rotate with constant
angular velocity (CAV), or constant linear velocity (CLV). CAV,
used by magnetic drives (and record players), is measured in RPM,
and means that the read head sweeps the same angle, for the same
amount of time, at all radii. CLV, used in CD-ROM, allows the
head to read the same length of track at all times and radii (1.3
meters/sec), which requires that the disc spin slower as the head
moves to the outer edge of the disc. A CD-ROM spins from 539 RPM
at the inner edge, to 210 RPM at the outer edge.
- Control Bytes
- The CD-ROM physical block structure specifies a data user
area of 2048 bytes and other sets of bytes, to make a full
sector--including the 98 control bytes. These control bytes,
with sub-channels at the bit level, are specified in the Red
Book. They are key for much of the functionality of CD
implementations.
See, Sector Structure
- Convergence
- A term in the industry that tries to explain the pressures on
optical technology, mainly CD-ROM development, to bridge the gap
between computer users and television viewers. The aim is,
ostensibly, to produce multimedia applications that would serve
and satisfy the needs of both groups, with one hardware device.
To some, the term even includes conjunction with the Internet and
other network services.
- Conversion
- Generally used to mean conversion of computer files from one
system to another, or from one format to another (DOS to Mac,
EBCDIC to ASCII, PCX to TIFF, and so on). In some cases,
conversion is used to mean putting the information on another
media--as in digitizing information that is on paper, in
microfiche, video, etc. Conversion is usually a key and expensive
part of the data preparation process. In fact, the growth of the
conversion industry is a reliable reflection of the growth of the
CD-ROM, optical imaging, and multimedia industries.
See, Data Preparation
- CPU
- The Central Processing Unit, or processor chip, is the
'brains' of the computer. For floating point computations, the
CPU employs the co-processor chip--if there is one present on the
motherboard. Current CPUs generally include a co-processor chip.
Database, spreadsheet, CAD-CAM and other vector graphics
applications, and most software decompression algorithms benefit
from the use of a co-processor. That is why some multimedia
applications work smoother with a fast CPU and a co-processor.
The MPC Level 2 requirements, however, include only a 486SX chip
(no co-processor), 4MBytes of RAM, and a 2X drive as a minimum--
which is not adequate for most current multimedia releases.
- CRC
- Cyclic Redundancy Check is a method for detecting errors in
data transfers. A special polynomial algorithm produces and uses
a coefficient and a remainder (usually 16 or 32 bits long) to
check if the transmission proceeded without problems. CRC values
change even if only one bit in the file changed--which makes CRC
extremely reliable for checking integrity of files transmitted
between computers.
- CRT
- Originally, somewhat appropriately, computer monitor screens
were dubbed CRTs, because the Cathode Ray Tube was its biggest
component. Current CRTs offer ever-increasing resolutions and
sophistication. Flat display technology, however, does not
employ the CRT and is becoming a competitor because it is no
longer used only in portable or notebook computers.
D
- Daisy Chain
- Peripheral devices connected serially are said to be 'daisy
chained,'--as in SCSI configurations. While a SCSI card uses
only one slot in the bus, all the devices in the daisy chain are
available, because each has a specific address, and the devices
in the chain respond only to the instructions addressed to them.
- DAT
- Digital Audio Tape, generally high-quality 4mm magnetic tape
in a cassette, with capacities up to over 1 Gigabyte, that has
been used in the computer arena mainly as an archival and back-up
medium. For CD-ROM, it is used as a transfer medium.
See, Transfer Media
- Data
- Plural of datum, in the sciences, refers to sets of figures,
measurements, expressions, etc. that, when expressed in a defined
framework, acquire meaning that makes then information. For
example, 45, 35, 75, are essentially meaningless figures (data);
but, when expressed in terms of degrees Fahrenheit, they mean
specific levels of temperature (information). In computer
terminology, however, data generally is used to mean files with
user information.
- Data Area
- This is the space in the track, specified by the ISO 9660
specifically for the sectors with user data. It is recorded
after the System Area, and is followed by the Lead out.
- Data Discman
- A Sony portable drive that plays Sony's 8cm discs, media
that was used initially for audio 'CD-singles.' Since l990, the
Data Discman plays CDs formatted according to the ISO 9660--which
can hold up to 200 Kb of information. More recent
implementations include compressed audio--using the CD-ROM-XA
format. For some reason, the DataDiscman has not become popular
in the US.
See, CD Singles
- Database
- In traditional computing, databases are structured
collections of fielded data sets that can be updated,
manipulated, indexed and used as sources of appropriate
information. With the advent of large collections of text,
graphics, and other types of information incorporated in single
applications, the concepts of database, media and information are
expanding.
- Data Preparation
- This is usually the most time-consuming and also the most
expensive part of the application production process. Since,
with rare exceptions, all the necessary data is usually in a mix
of media, file formats, databases and others, it takes a lot of
preparation and work to get them in the shape and formats
appropriate for use in the CD-ROM application. Therefore, data
preparation must be a carefully planned step in the process.
See, Conversion
- Data Transfer Rate
- This is, essentially, the reading speed of the original CD-
ROM drives (150 kb/sec). Since the computer can handle data at
higher speeds, manufacturers are now offering 2X, 4X, 6X and even
higher speed drives. Some trade magazines are already previewing
12X drives.
See, CD-ROM Drives
- DBMS
- A Database Management System generally involves policies
about the coordination of data entry, database operations,
output, access, and information security in an organization.
Systems vary in size and sophistication, and there are many
appropriate software DBMS front-ends in all platforms, and more
and more DBMS include CD-ROM as their archival medium.
- DCT
- Discrete Cosine Transform is a mathematical algorithm used in
compression/decompression programs, especially for color graphics
and motion video--such as in JPEG and MPEG. MPEG-1 uses DCT for
intraframe compression. MPEG's high rates of compression,
however, are due mainly to its interframe compression.
- Demodulation
- In data communications, transmission through telephone lines
involves modulation at one end, and demodulation at the other
end. For this purpose, computers use the modem.
See, Modem
- Digital
- Generally contrasted to analog, digital refers to the use of
digits (0-9), in specific code schemes. The binary coding scheme
uses 1s and 0s, and is the basis for digital computers. Although
analog computers were developed, binary processors rule
technology--from cheap consumer items to Cray supercomputers.
- Digital Audio
- The Red Book specifies the quality of digital audio to be
encoded in a CD-Digital Audio product, although that quality is
also used in other platforms. The sound is sampled at 44.1KHz,
and quantized at 16 bits/sample for high quality stereo sound
(65,536 values). Sound of different quality, even if it is
placed in a CD, is not Red Book Digital Audio.
See, CD-Digital Audio
- Digital Video Disc
- See, DVD
- Digitization
- Digitization generally refers to the process of translating
or converting data and information (in paper, analog sound
tracks, graphics, etc..) into binary coded files for use in
computers. Text can be keystroked or OCR'd, graphics are
scanned, video is digitized, sound is sampled and quantized, and
so on. Digitization is the heart of the new conversion industry.
See, Conversion
- DiscMan
- See, Data DiscMan
- Disc Read Head
- Storage drives (magnetic and optical) have a head or heads
that float over the recorded area to read and write. Obviously,
CD-ROM drives have only a read head, which involves a
low-intensity red laser diode (a.k.a. infrared laser diode),
lenses that focus the laser on the track, and others that
redirect the reflections to one of the photodiodes for
appropriate decoding. Some Write-Once and Rewritable optical
drives involve two heads (to write and read), while other drives,
including CD-Recordable, use only one head to do both--using a
high-intensity blue argon laser for the write function. For mass
replication of CD-Audio and CD-ROM discs, the glass master is
produced by encoders that have special recording heads.
- Disc Write Head
- See, Disc Read Head
- Disk Sector
- In magnetic disks, formatting, provides a geography of the
platters; which are divided into concentric circles, and these
circles are further subdivided into sectors. Although sectors
vary in size depending on their position in the disk, they have a
specific capacity in bytes. This sectored framework is found in
constant angular velocity (CAV) drives, and is compatible with
the FAT used in PCs. When discussing optical discs (with c),
'sector' is used to refer to discrete amounts of data with a
specific layout or structure along the track.
See, Sector Structure
- DMA
- Direct Memory Access takes place when an input/output device
(hardware), or an application (software), issues calls or writes
directly to system memory--while the CPU, essentially, lets that
happen. MS-DOS implements a table of DMA channels for that
purpose.
- DOS
- Disk Operating Systems pertain to microcomputers. In fact,
early microcomputers operated with one of various operating
systems. When IBM chose the operating system developed by
Microsoft, which could handle hard and floppy disks, it was
called Microsoft Disk Operating System. Since then, all
operating systems for microcomputers, especially IBM-compatibles,
are called DOS (MS-DOS, IBM-DOS, Dr. DOS, 4-DOS, etc.).
- Double-layer CD
- Recently, it refers to the technology developed by 3M, which
allows production of a CD with two recordable layers on the same
side. To read it, the single head shifts the laser's focal
length appropriately. Double-layer CDs will become common, since
the industry agreed to make it part of the specifications for the
DVD format.
- Double Spin
- See, Transfer Rate
- Double Density CD
- This name has been applied to the CD format proposed by
Nimbus Technology and Engineering (1994). It claims to encode
more than two hours of a CD, by increasing the number of tracks
per inch. Double density, and more, was also demonstrated by
Optical Disc Corporation (ODC), which proposed its own High
Density CD specifications in late 1993. These efforts, however,
have not attracted the attention that Philips, Sony, Matshushita
and the other established players received for their
specifications that led to the industry's Digital Video Disc.
See, DVD
- DRAW
- Direct Read After Write was an expression originally used to
differentiate W-O and Rewritable from CD-ROM technology. DRAW
implied that W-O and Rewritable disks could be accessed or read
immediately after being written to, while CD-ROM could
not--because, by design, it had to be mass replicated first.
- Driver
- In computers, driver refers to a device driver, which is
software that, under CPU control, implements device I/O functions
or other functionality (video, sharing, graphics, printer, mouse,
etc.).
- DSP
- Digital Signal Processors are specialized processor chips
used for diverse functions, especially in modems, sound boards
and serial ports.
- DVI
- Digital Video Interactive, developed by Intel and IBM, is
conceptually similar to CD-I. DV-I, however, emphasizes a
compression scheme that employs proprietary chip sets (for
compression and decompression of audio and video) that require
add-on boards. These DV-I boards display VHS quality full-motion
video. But, the surge of applications implementing the MPEG
standard has affected the growth of DVI. It is, however, still
used in public information, education and training.
- DVD
- Digital Video Disc is an upcoming product. Nimbus and Optical
Disc Corporations (ODC) already showed their capabilities to
master double density, and Philips quad-density CDs. The emphasis
turned, however, on the Digital Video Disc. One camp, headed by
Sony and Phillips, first promoted the MultiMedia CD, and then the
High Density CD (HDCD,1994). The other camp, headed by Toshiba
and Times-Warner, promoted the SuperDensity CD (SDCD) and
changing the name, proposed the DVD (Jan95). The HDCD
specifications included single and dual-layered, single and dual-
sided CDs--with corresponding capacities from 1.3 to 7.4 GB, and
playing times from 47 to 270 minutes. The early DVD
specifications included single and double-sided CDs, with
capacities of 5 to 10 GB, and playing times from 135 to 270
minutes. It was understood that MPEG-1 was included.
To keep within the traditions of the industry, these two
camps, after the compulsory maneuvering, were helped in their
decision to compromise on a single set of specifications for DVD.
The announcement of the compromise specifications (Sep95)
mentioned a double-layer single-sided CD with a capacity of
4.7GB, the use of EFM+ signal modulation, and another version of
the Reed-Solomon error detection and correction schemes.
Most analysts thought the announcement satisfied the video
industry's need for a disk with sufficient playing time for a
full-length movie, compatible with MPEG-2, and backward
compatible. There is, however, ample flexibility in the
specifications for single-layer, and double-sided double-layer
CDs, of varied capacities. Applications in DVD format are
expected by mid-1996.
E
- EBCDIC
- Extended Binary Coded Decimal Interchange Code, is an 8-bit,
no parity, 256 character code (in several variations), used
mainly in IBM mainframes and related platforms. Unlike the
'extended' ASCII character sets, EBCDIC variants are not
standard. Conversion between EBCDIC and ASCII platforms is
therefore not an automatic process.
See, ASCII
- EFM
- Eight to Fourteen Modulation is used during encoding, because
the 8-bit 'magnetic' byte has to be modulated to a 14-bit
'optical' byte. Technically, this modulation is necessary to
allow encoding of two consecutive 1s--which would be impossible
with the scheme of pits and lands using 8-bit bytes (1s and 0s).
In fact, the changes in reflectivity (as the laser light moves
along the sequence of pits and lands) are coded as 1 channel
bits. Two consecutive 1s are therefore not possible. Moreover,
the 'lands' in between the 1s are represented by 0 channel bits,
and the number of 0s represent the run-length. The bits in an
optical byte are known as 'channel bits' to avoid confusion, and
because they are transferred to the controller board through a
specific channel. Furthermore, the fourteen-bit optical byte is
provided three additional channel bits, known as merging bits--to
eliminate transition conflicts between consecutive optical bytes.
During the read process, the interface card demodulates the 14-
bit optical code to the 8-bit code used by the computer--and all
channel bit-level modulation and processing remain transparent to
the user.
- EISA Bus
- The Extended ISA Bus, was introduced by PC manufacturers as
their alternative to the IBM MCA bus. It is also a 32-bit bus,
supports high speed data transfers, allows post-installation
configuration of adapter cards, and can access higher amounts of
system RAM. Unlike the ISA bus, the EISA bus does not support 8-
bit adapter cards. PCI buses with Pentium CPUs seem to have hurt
EISA standings.
- Electroforming
- In jewelry, it is used to lay fine gold or silver surfaces on
complicated pieces, or on extremely fine shapes and surface
configurations, because the electromagnetic field sets the fine
metallic particles in place. In the CD industry, where the pits
in the glass master are measured in tenths of microns,
electroforming is used to 'form' the initial metallic (nickel)
mold that is used to produce the stampers for the injection
molding machines.
See, Glass Master
Mastering
- Encoding
- In the computer arena, programmers and users see and work
with higher level languages, but the processors deal with machine
languages and binary code. To use optical technology, it was
necessary to develop an encoding scheme that would produce the 8-
bit computer bytes, while using the pits and lands produced by
the laser on the disc surface. The resulting optical encoding
scheme, uses a 14-bit byte modulated from the 8-bit byte--in
which the 1s represent the transitions between lands and pits,
and the 0s represent the run-lengths. The mastering machines do
the encoding, and the controller card of the drive does all the
decoding.
- Encoding Technologies
- See, Optical Recording Technologies
- EPROM
- Erasable Programmable Read Only Memory chips are being used
increasingly more. Until recently, all important hardware
configuration, BIOS, and other defined information was stored in
ROM chips--to prevent accidental erasures or modifications. But,
with EPROMs, knowledgeable users can reprogram ('burn') the code
in those chips as deemed necessary. EPROMs are also used to
provide firmware for higher end hardware configurations.
- Erasable
- In optical technology, erasable generally referred to optical
drives that allow the user to write and erase at will--just as
with magnetic hard drives. Currently, however, the preferred
term is rewritable, as in magneto-optical rewritable technology.
See, M-O Technology
- Error Detection Codes (EDCs) and Error
Correction Codes (ECCs)
- For data integrity, CD-Audio includes two levels of CIRC
error detection and correction, as specified in the Red Book.
Because computer data requires higher that audio levels of
integrity, the Yellow Book specified a third level of such codes
in each CD-ROM sector (4 bytes EDC and 276 bytes ECC). This
third level involves a layered error detection and correction
scheme, and is sometimes referred to as the Block Error
Correction codes.
See, Integrity
CIRC
Sector Structure
- Error Rate
- See, BLER
- Exabyte
- Originally a brand name, it is used commonly to refer to the
high quality, 8mm wide, magnetic tape (designed for video), in
special cassettes, of capacities up to over 2 GBytes, currently
used in the computer arena mainly as an archival medium, and in
tape libraries--also manufactured by Exabyte. In CD-ROM, 8mm
Exabyte tapes are used as a transfer medium.
See, Transfer Media
- Expansion Bus
- Because of the growth in computer devices, some users fill
all available slots in the main bus. Expansion buses, some of
them proprietary, as in the early 'luggables,' allow users to
connect other controller cards and devices to the main bus.
F
- Fielded database
- Some years ago, this phrase would have been considered
redundant, since databases were composed of data in fields. But,
since the advent of large collections of text, and since the noun
textbase did not catch on, 'fielded databases' and 'fulltext
databases' are widely used. Fielded databases are, essentially,
those that do things with data in fields--the way dBase and
others do.
See, Full-text Database
- Floptical Disk
- The name implies the physical nature of a floppy disc and
optical technology, but the floptical disk is a magnetic disk. It
uses optical technology only to align the head along the tracks,
which are at a much higher density than regular floppy disks.
That density accounts for its capacity--about 20 MBytes. But,
floptical disks did not fare as first expected.
- Foreign File Access
- The Apple operating system provides Foreign File Access to
allow reading of CD-Audio and CD-ROM (ISO 9660 and HSF) discs.
In a quite different option, ISO 9660 discs can be read by Apple
computers that have the Apple Extensions for ISO 9660--which,
essentially, make the CD-ROM look like an HFS-formatted disc.
See, MSCDEX.EXE
- Format
- In the computer arena, there are physical and logical formats
for storage devices. Magnetic storage devices implement a
physical structure (MFM, RLE, IDE, SCSI, etc.). A high level
formatting program establishes its physical layout, and a low
level format assigns logical identities and file allocation
tables to all its partitions. CD-ROM discs use the physical
format defined by the Red Book (which defines the size, tracking,
sector contents, etc.). The standard logical format is defined
by the ISO 9660, the volume and file structure that was the key
for the growth of CD-ROM.
See, ISO 9660
- Frame
- Commonly, frames imply the basic elements of display.
Television, we say, displays 30 frames per second. In CD-ROM,
however, a frame is not related to display. During mastering,
the CD-ROM sector is subdivided into 98 frames, and the bytes in
those frames are modulated from 8 to 14 bit structures. In fact,
those new optical bytes are provided with three merging bits, to
eliminate conflicts between bytes. The chain of bits thus
produced are used by the encoder, to 'burn' the pits and leave
the lands on the recording layer of the glass master.
Nevertheless, all these things are done by the mastering
equipment, and are transparent to the user.
- Frankfurt Group
- A group of the industry's top firms met in Frankfurt, in
1991, and proposed an ISO 9660-compatible standard for multi-
session recording--which was not part of the ISO 9660. They also
supported the Rock Ridge Proposal, which deals with
multi-platform volumes. The Frankfurt Group's proposal,
published by ECMA as Working Paper TC 15, deals with logical
specifications for the Orange Book, Part II (W-O). It
establishes two types of file structures: Type 1 is compatible
with other ISO 9660 discs, and can be read by a standard drive.
Type 2 allows 'incremental multi-session recording' in a CD-WO
volume. Hybrid Discs include both types of file systems, but
standard drives could only read the Type 1 area--but, more
importantly, the Type 2 areas would allow recording applications
that can be used by different operating systems or platforms.
Approval was expected in late 1995, and new operating systems
were expected to support the resulting standard.
See, Multi-session
- Full-text Database
- Essentially, this is a large collection of textual
information or documents--ready to be managed by a full-text
retrieval software package. Therefore, a large collection of
text files alone does not a full-text database make. If however,
they are configured and indexed for software that can perform
searches across all of them, and perform output functions, then
and only then you have a full-text database.
G
- Glass Master
- This product of the mastering process involves a large glass
disc, duly prepared and coated with a recording layer--usually
Photoresist. After recording, the glass master goes through a
special chemical process (akin to development), and is then
metallized. The metallized glass master, also referred to as the
'positive,' is submitted to electroforming, to produce the
metallic (usually nickel) master--which is necessary for
producing the stampers for the injection molding machines.
See, Mastering
- Green Book
- Published by Philips and Sony in l986, the Green Book uses
the ISO 9660 to establish the block structure for CD-I,
addressing problems of synchronization and use of file
compression for multimedia applications (CD-Audio, other audio,
data, graphics and video). Although it looks like a CD-ROM XA
sector, a CD-I sector uses the area (8 bytes) left unused in the
Yellow Book CD-ROM sector structure in a different way.
See,
CD-I
- GUI
- Graphical User Interfaces are becoming predominant. Computer
operating systems are designed to work, out of the box,
implementing the command line (prompt), in the basic text mode
screen (80x25 for PCs and 80x24 for Unix terminals, etc.). But,
the growth and popularity of graphical applications led to the
implementation of graphical user interfaces. GUIs work in
graphics mode; that is, they display everything on the screen as
a graphic and, instead of the command line, they implement menus
and other graphic objects that are operated with special
keystrokes or a pointer device--the ubiquitous mouse. Microsoft
Windows is the predominant graphical user interface in the
IBM-compatible platform, and others predominate in the OS/2,
UNIX, and other operating systems.
H
- Hard Drives
- Originally known as Winchester drives, these magnetic storage
devices have one or more non-removable solid platters--as opposed
to the floppy-disk drives. Hard drives come in various types,
different capacities and configurations--and are connected to the
bus through a controller or interface card. There are removable
hard drives, which allow removal of the component that contains
the platters--a workable option for users with security concerns.
See, Format
- HDTV
- High Definition Television has been in use in Japan and
Europe for some time. The US has been trying to convince all
(especially the Japanese) to use the HDTV specifications
developed by the US industry, thereby delaying implementation of
HDTV in the US. Expectations were that the US may yet win the
specifications contest.
- Header
- In computer circles, headers meant a set number of bytes at
the 'head' of the file--with information about the file,
especially necessary when dealing with large numbers of files in
tapes. In current PC usage, the term refers more often to
headers of graphics files. A TIFF file, for example, can have
extensive functionality because the TIFF header has broad
features and flexibility. Graphics headers, however, can become
problematic, because specifications about headers are rather
liberal and too many developers include in the headers additional
information useful to their applications. But, those efforts
often cause problems when other applications try to use those
files.
- High Density CD Formats
- See, DVD
Double Density CD
- High Sierra Format
- The development of the High Sierra Format is part of the
industry's interesting history. After the publication of the
Yellow Book, facing the growth of CD-ROM applications in
proprietary formats, representatives of the major firms in the
industry met at the Del Webb's High Sierra Hotel and Casino, in
Lake Tahoe, Nevada, to agree on basic specifications for a common
logical format and file structure for CD-ROM. Soonafter, they
published the "Working Paper for Information Processing: Volume
and File Structure for CD-ROM Information Exchange (1986)," since
known as the High Sierra Format (HSF). Their unprecedented
effort proved to be key for the effective role of standards in
the CD-ROM industry. And, to their credit, the ISO 9660 is
essentially their Working Paper with some pertinent modifications
and extensions. Today, only organizations that do not distribute
their CD-ROM application beyond their organization are still
producing HSF discs.
See, ISO 9660
- Hit
- In search and retrieve applications, hits refer to the
matches or instances found by the software. Most applications
remind the user to combine search parameters appropriately to
generate efficient (narrowed down) searches and produce the most
relevant results or matches.
- Hollywood Digital Video Advisory
Group
- A committee of representatives of the entertainment industry
(Columbia, Disney, MCA/Universal, MGM, Paramount, Viacom, Warner
Bros., et al.) that met in l994, and proposed their guidelines
for a desired DVD product. Those guidelines were important for
the compromises towards the final DVD specifications.
See, DVD
- HPSB
- The High Performance Serial Bus, developed by the IEEE,
specifies a no-loop bus that can connect up to 63 devices on a
single bus. The base transfer rate is 100Mbits/sec, and highest
expected transfer rate is 400Mbits/sec--to accommodate future
devices and PCMCIA features. HPSB, as an interface between
devices, does not specify its own packet protocol; it will use
other protocols. ANSI is apparently adapting SCSI-3
specifications (command, transfer and control schemes) for its
own specifications for use with the HPSB.
See, Bus
SCSI
- Hub
- This is the central hole of the optical disc. The spindle of
the drive clamps the disc by this hub, which should fit rather
precisely to provide reliable centering and eliminate flutter.
- Hypercard
- Interface card and software for Macintosh computers, to use
and produce multimedia applications. The software development
tool in the recent version 2.3 includes text-to-speech (with
Plain-talk software) and other up-to-date capabilities. Since
Hypercard was bundled with the Macintosh, its users have been
spared the problems of compatibility and upgradability of the
multimedia kits and peripherals in the IBM-compatible world.
- HyTime
- Hypermedia/Time-based Structured Language is an international
standard (ISO/IEC 10744:1992) for an SGML-based set of semantic
extensions to SGML. They help structure or represent hypertext
and multimedia elements in SGML documents--recent proposed
extensions involve maps, music scores and others. Promoters of
HyTime aim to add multimedia functionality to SGML-based
documents, in system-independent applications.
I
- IDE Interface
- The Intelligent Device Electronics interface supports ISA,
EISA or MCA buses, and is much smaller than the original disk
controller cards. IDE hard drives include most of the circuitry
that previously resided in the interface card. The growth of
multimedia helped the growth of sound cards and of IDE controller
cards that support CD-ROM drives.
- Image
- After the application works as desired, in the PC, the data,
retrieval software, indexes, interface, and other files are
placed in the desired order--aiming for their most efficient
location in the eventual CD-ROM. Usually, the application is
tested at this stage. And, then, this collection of files, in
appropriate block sizes, along with descriptors, etc., is written
as a large file, to a transfer medium to be sent for
premastering. That collection is therefore known as the 'CD-ROM
image' or just 'image.' More precisely, an 'ISO image,' refers
to the contents of a disc that will be premastered to an ISO 9660
volume structure.
See, Premastering
- Imaging
- This relatively new term refers to the use of computers to
work with graphics, as well as conversion of documents to
computer usable graphics formats (generally TIFF or PCX format).
The imaging hardware and software industries have been high
growth industries these past years. In fact, the multimedia,
archiving, online document management, and other arenas are
certainly poised to keep it that way.
- Implementation Levels
- The ISO 9660 specifies three Interchange Levels--which deal
with file naming and their use by different operating systems.
But, since some operating systems can not implement the
interchange levels effectively, the ISO 9660 defines two levels
of implementation. Implementation Level 1 allows producers to
limit their implementation of the features of the chosen
interchange level. Level 2 specifies that all the features of
the ISO 9660 interchange levels must be supported. In the IBM-
compatible world, for example, because MSCDEX.EXE supports only
Implementation Level 1, some features specified in the
interchange levels are generally not used, and others are used
with some limitations (path lengths, characters to be used in
filenames, number of directory levels, and others).
See, Interchange Levels
- Indeo Video
- This codec, introduced by Intel, supports high quality video
(320x240) that is used in multimedia applications, and allows
software-only playback with PCs with 486 or Pentium CPUs. It is
also supported by Microsoft's Video for Windows and Apple's Quick
Time--which also has a Windows version. Intel's Indeo supported
vector quantization technology, but the recently introduced
version 3.2, Indeo VI (video interactive), is said to support a
new hybrid wavelet-based technology. As with previous versions,
developers can use Indeo VI royalty-free.
See, QuickTime
- Indexing
- In CD-ROM, indexing involves assigning searchable
'addresses' within a track--which can be up to 99. But, in data
management, indexing involves creating sets or tables of pointers
to the records or information in the database. With the new
processors, complex indexing is used for search and retrieve
functions in large and sophisticated databases or large
collections of text. Nevertheless, indexes or the 'indexing
overhead' for large full-text databases can take up considerable
space in the CD.
See, Full-text Database
- Injection Molding
- This is a common industrial process to produce plastic
products of all shapes. The CD-Digital Audio mastering and
replication plants are costly and highly clean environments,
because of the precision required to produce acceptable CDs. The
injection molding machines fitted with appropriate stampers,
stamp or press the molten polycarbonate. Thus, the replicate
(also known as substrate) is allowed to cool before it is moved
for metallizing and given a coat of protective lacquer. Most
injection molding machines produce about 5 replicates per minute;
some of the newer machines run at near double that rate.
- Integrity
- Integrity is another conceptualization of reliability. It is
often expressed as a number of erroneous bytes (characters) read
per number of bytes read--after error detection and correction.
The Yellow Book specifies a much more effective scheme than that
in the Red Book. In fact, the industry's figures for CD-ROM
integrity are 1 in 10 exp(13)--or about one erroneous byte in ten
trillion! Assuming that two CD-ROMs involve about a gigabyte, we
should expect an erroneous byte in about 5,000 CD-ROMs!
See,
CIRC
Error Detection...
- Interchange Levels
- The ISO 9660 defines three downward compatible levels of
interchange--which define the length of filenames, and the ways
they can be recorded in a CD-ROM. Level 1, which is more
restrictive but compatible with MS-DOS, is obviously the most
commonly implemented. The expectation is that the increasing
demand for multi-platform applications will push the
implementation of levels 2 and maybe even level 3 features.
See, Implementation Levels
- Interface
- In computers, a user interface is that software component
that the user sees, interacts with, and employs to control and
navigate the application. In more sophisticated database
environments, common interfaces refer to software programs that
enable users and operators in different computer environments,
when appropriately connected, operate a specific program on a
main computer or network.
- Interleaving
- In terms of CD-ROM encoding, where the track is a single
spiral line, it means the appropriate interposition of portions
of files, of different data types (text, video, audio, graphics,
etc.), so that the application can use it for the most
coordinated display or output (making it seem as displaying
varied data types at the same time). The process is performed at
the sector or logical block level (if the sector has been broken
down to that level). Although the ISO 9660 provides
specifications for interleaving, it seems that only CD-ROM-XA
applications have implemented them with success.
- ISA Bus
- The Industry Standard Architecture bus, introduced by IBM in
the early l980s, is a motherboard with a 16-bit data bus that was
freely copied for the manufacturing of IBM-compatible PCs.
Although never approved by a standards-setting organization, the
ISA bus was common to most 286, 386, and 486 Pcs. Its
limitations became clear in face of the new faster CPUs (486,
Pentium, etc.) that can operate on 32-bit data slices or chunks,
and can address larger amounts of RAM. Today, only low-end PCs
are sold with ISA bus motherboards.
- ISO
- The International Standards Organization, composed of scores
of international specialized committees, with main Secretariats
worldwide, is the accepted source of standards for electronic and
computerized data communications and information processing
within the Open Systems Interconnection (OSI) framework.
- ISO 9660
- Issued by the International Standards Organization, its
formal title is ISO 9660: Information Processing--Volume and File
Structure of CD-ROM for Information Exchange (1988). This multi-
platform logical structure has been the key standard for the
growth and worldwide acceptance of CD-ROM as a publishing and
information distribution media and, since then, as the basic
format structure for other implementations of CD-ROM in the
computer arena.
See, Standards
J
- Jewel Case
- This is the plastic shipping and storage case for CDs.
Although the original practical design of the jewel case received
no compliments, it is still used throughout the industry. There
is, however, a veritable growth industry in light CD-ROM mailers,
storage packets, and colorful mailers--especially for promotional
mailings.
- JPEG
- A versatile and commonly used color graphics compression
specification adopted by the Joint Photographic Experts Group.
Hardware and software JPEG implementations allow setting the
desired compression, from 24-bit lossless (usually 2:1) to
smaller bit size lossy compression rates (up to 60:1 in some
cases). This allows users to insure retention of detail and
precision of the original. For everyday graphics work,
recommended JPEG compression ratios range between 25 and 35:1.
- Jukebox
- CD-ROM jukeboxes allow users to access collections of
CD-ROMs. There are various types of CD-ROM jukeboxes, with
different capacities (Pioneer has one with 500 CDs, and Disc
apparently has one with 1478 CDs.). Some implement more than one
drive, and other recent versions claim to support major LAN
configurations. Some jukeboxes can be configured with multiple
drives and even CD-R 'writers.' Some use 'optical jukebox' to
refer to jukeboxes with WORM and Rewritable discs.
See, CD-ROM Tower
K
- Kbps
- Kilobits per second (1000 bits/sec) is a measure used mainly
in computer communications, for transmission rates and hardware
bandwidths.
- Kilobyte
- In computer usage, this basic number means 1024 bytes, which
is 2 to the tenth power. It is used to account storage capacity,
file lengths, and other byte-related amounts. Currently, larger
multiples are already in everyday use, such as Megabyte, Gigabyte
and so on.
- Kodak Photo CD
- This product, was introduced by Kodak and Philips, in l992.
The Photo CD is a hybrid disc that uses the CD-ROM XA Form 1
sector structure to store up to 100 35mm photographs in one disc,
in one or more sessions. The photographs are scanned into digital
files (18 MBytes--compressed to about 4.5 MBytes, each), in five
different resolutions. The Kodak Photo CD player displays on a
TV monitor, but a multi-session CD-ROM XA drive, with appropriate
software, can display on a PC monitor. When issued as a Bridge
Disc, it can be played by Photo CD and CD-I drives connected to a
TV set. Older CD-ROM XA players need an appropriate interface
(or a software patch) to display multi-session contents.
See, Multi-session
L
- Label
- CD-ROM, and other optical discs, are usually labelled on the
'back' side. Earlier, the label was generally screen-printed at
the replication plant, in up to three colors, as part of the
basic price. Today other printing options are also used,
including some for the desktop as well as do-it-yourself kits
designed for CD-Recordable one-offs. While labels have specific
information about the product, they should also include the
industry's 'DISC' logo that identifies the disc as an CD-Audio,
CD-ROM, CD-I, etc.
- LAN
- Local Area Network (LAN) and Wide Area Network (WAN)
technologies have incorporated optical devices into most of their
architectures. Some sophisticated servers now enable multi-user
access to CD-ROM drives and CD-R recorders throughout the
network.
- Lands
- During recording of a glass master disc, a high power
concentrated blue argon laser beam burns pits on the specially
prepared recording surface. The 'lands' are the clear spaces
between those pits. During reading, since the lands and pits
reflect the read laser light differently, the transitions between
them are detected and decoded to produce the 1s, and the lands
provide the 0s, in run lengths.
- Laser
- Light Amplification by Stimulated Emission of Radiation was
demonstrated about half a century ago, with an original ruby
laser. Today, lasers abound to suit diverse technologies and
applications. Some magazines have reported tests of blue lasers
of higher precision, which will make possible higher density
optical discs.
See, Blue Laser
- LaserCard
- A small card that has a special backing (includes a
recordable layer), and can be recorded and read by special drives
(optical card readers). The Drexler process employs ablative
write-once technology, and can store about 3MB of data.
- LaserVision
- Introduced in l978, the LaserVision disc was one of the
original implementations of optical technology. It was used to
record video (analog), and became prominent in the interactive
video training and educational market. With the popularization of
PCs, LaserVision was used in the eighties in applications that
combined PC software and interactive video.
- Lead In--Lead Out
- These are lengths of track before the beginning and after the
end of the coding. In single session applications, they serve as
'markers;' the lead-in includes the Table of Contents, and the
lead-out can include code to stop the player--since there is no
more application code in the track. CD-Audio tracks (songs)
implement lead in and lead out to help song selection. In
mixed-mode applications, each track with different type of data
(text, video, audio) is required to include pre-gap and post-gap
spaces.
- Logical Structure
- In the computer industry, operating systems are designed to
use a particular logical structure for data storage. For CD-ROM,
however, the ISO 9660 specified the standard volume and file
format to serve various computer platforms or operating systems.
With appropriate modifications, this standard is making it
possible for CD-ROM to involve text, graphics, audio and video
for various types of CD-ROM implementations.
See, ISO 9660
Standards
- Lossy/Lossless Compression
- Certain compression algorithms can produce outstanding
compression ratios, but often at the cost of imperfect
decompression; that is, the decompressed data is not identical to
what it was before compression. Imperfect decompression (even if
only a few bits per millions of bits) is called lossy--because of
the loss of bits affects data integrity. Lossless compression,
on the other hand, employs algorithms that do not lose data in
decompression, and although they may not produce great
compression ratios, they provide integrity or reliability. When
working with graphics and sound, some lossy compression is
considered adequate, especially when storage space is a serious
consideration.
See, Compression
M
- Mass storage
- This is a relative concept. When PCs were introduced, 10 MB
hard drives were considered adequate mass-storage devices--with
little argument. For current PCs, magnetic disks of one gigabyte
or two, CD-ROMs and optical discs are common mass storage
options. Indeed, the pressure for larger storage devices will
continue. It is likely, however, that mass storage in the future
will involve chips, or cards, rather than magnetic or optical
discs.
- Mastering
- Mastering involves producing a glass master disc that is
necessary for the mass reproduction process. Mastering takes
place in a 'clean' environment, where the encoders use a high
power blue argon laser beam to 'burn' pits on a large glass disc
coated with a sensitive recording layer (usually photoresist).
Once treated or 'developed' (chemically), the glass disc is
referred to as the master or positive. Using electroforming
technology, this glass master serves for the production of a
metallic master (usually nickel), generally known as the
'father.' (It is also called a stamper, if it is used for
reproduction of small runs.) For large mass reproduction jobs,
the 'father' is used to produce intermediate 'mother' molds which
are used to produced the necessary metal stampers ('sons' or
production stampers) that are used in the injection molding
machines. Mastering and reproduction are usually done at the
same plant.
See, Injection Molding
- Matches
- See, Hit
- MCA Bus
- Micro-Channel Architecture Bus, introduced by IBM in 1987, is
a 32-bit bus that can allow access to over 64 MBytes of system
RAM. The versatile MCA bus, also allows post-installation
configuration of adapter cards using a software program. At the
outset, because very few CD-ROM manufacturers supported fully the
MCA bus, users faced higher prices for CD-ROM drives with
controller cards for the MCA bus. For various reasons, the PC
industry has not followed IBM in the use of micro-channel
technology.
- MD (Mini-disc)
- See, Data DiscMan
- Media
- In the computer arena, media usually refers to storage media-
-which are varied and changing (glass or metal discs with
magnetic coating, plastic discs with magnetic coating, CD-
Recordable discs, paper cards with magnetic coating, etc.). In
CD-ROM circles, media most often refers to archival and transfer
media. Thus, at first, CD-ROM images were placed on magnetic 9-
track 1/2 inch tapes for transfer to mastering plants. Then, 4
and 8mm Exabyte tape cartridges became widely used. Recently, CD-
Recordable discs (one-offs) are becoming the preferred
transfer media. All these transfer media are accepted by most
mastering and replication plants.
See, Image
- Megabyte
- A Megabyte (MB) is 1024 KBytes, or 1,048,576 bytes.
- Metallic coating
- After injection-molding and cooling, each disc undergoes
metallizing--a process that gives the CD a metallic coat and its
typical shiny surface. This coating reflects the laser light
during the read process. For mass reproduced CDs, this coating is
generally aluminum, but CD-Recordable, Write-Once and Rewritable
discs use a gold-based coating for the same purposes.
- MIDI
- Musical Instrument Digital Interface, provides a coding
format for reproduction of sound in MIDI instruments. MIDI
interface cards allow computers and other equipment use the MIDI
coding. Most sound cards support the MIDI format. Because it
does not involve sounds, but instructions and codes about the
properties of the sound, the MIDI format is platform independent,
and computer users can manipulate MIDI files to great advantage.
Plenty of MIDI files are available in public bulletin boards and
other sources.
- Micron
- One millionth of a meter, a thousand of a millimeter. The
CD-ROM track is generally 2.2 microns wide, and the pits are
about 0.6 microns wide.
- Microsecond
- One millionth of a second.
- Mini-CD
- See, Data Discman
- Mini-Disc
- An erasable optical disc, usually 8cm in diameter.
- Mixed-Mode Disc
- Mixed-mode refers to a CD-ROM that includes CD-Digital Audio
sound. Generally, the application (programs, data, indexes,
etc.) are in Track 1, which is Mode 1. Audio begins in Track 2,
and can be up to 98 CD-DA tracks. For Mixed-Mode discs, most CD-
ROM players are equipped with CD-DA audio output plugs (except
some earlier models). Similarly, the earlier CD-DA players did
not have the feature that would ignore the data track of Mixed-
Mode discs, which resulted in harsh sounds when that first track
with data was 'played.'
- M-O Technology
- Magneto-optical technology is the most used recording
technology in the Rewritable (a.k.a. Erasable) line of optical
products. The substrate is covered with a complex stack of thin
films or layers--one of them the recording layer (of iron, cobalt
and terbium), in which the pits are recorded. Two such discs are
glued together to make the 5.25in, double-sided M-O
disc--although double-sided 8cm (3.5in) discs are used in some
devices. M-O discs can be rewritten millions of times, because
the technology employs a magnetic field to realign (polarize) the
molecular structure of the pit to its original unwritten state.
This process exploits the Curie and Kerr effects, and does not
move or effect physical changes in the coding layer, and
therefore accounts for the functionality of the rewritable disc.
The major drawback some see in M-O is that the process takes
multiple passes to seek the area, erase, write, and verify--
which, according to detractors, make it a slow performer. Under
the rather recent Orange Book, Part 1 (M-O), magneto-optical
technology is employed on the 12cm CD, formatted following the
ISO 9660 specifications. Unlike the M-O discs with proprietary
formats in various sizes, the standard CD-MO product has given
rise to new types of drives. The multi-function drives, for
example, are able to read and write the CD-MO ('Rewritable CD')
and read a standard ISO 9660 CD-ROM as well. There is expectancy
for the growth of the CD-MO technology in the PC platform.
See, Encoding Technologies
- Mode 1
- Under the ISO 9660, a CD-ROM sector can be Mode 1 or Mode 2.
Mode 1 allocates 2048 bytes for user data, plus a third layer of
error detection and error correction codes. This is the Mode that
provides the highest integrity for computer data.
See, Sector Structure
Integrity
- Mode 2
- Under the ISO 9660, a Mode 2 CD-ROM sector allocates 2336
bytes for user data, and the additional codes for only the first
two levels of error detection and error correction. It is
therefore generally used for segments of music or graphics, and
in CD-ROM-XA and CD-I implementations.
See, Sector Structure
Integrity
- Modem
- A computer peripheral device that employs a digital to analog
converter (DAC) to MOdulate and DEModulate the data stream from
binary to analog and viceversa. Therefore, modems allow
transmission of computer data through telephone lines.
See,
A-D Conversion
- Modulation
- Modulation is generally used to refer to analog to digital
conversion. There are however, various other modulation schemes.
For example, CD Audio players use a digital to Analog converter
to produce the stereo analog music signals. To produce the
appropriate mix of sounds in the signal, the system uses Pulse
Code Modulation (PCM)--although Adaptive Digital Pulse Code
Modulation (ADPCM), and others, have been implemented in other
audio applications.
See, ADPCM
EFM
PCM
- MPEG
- A CODEC adopted by ISO's Motion Pictures Expert Group for
compression and playback of full-motion video and audio streams--
often referred to as 'MPEG video.' MPEG-1 is now an open
standard (ISO/IEC 11172, 1991)--which establishes the structure
for a standard MPEG file, and specifies a transfer rate of
1.5Mb/sec, with a resolution of 352x240 at 30 fps. MPEG-2
accepts transfer rates up to 15MB/sec, with a high resolution of
720x480 at 30 fps, and it also requires a 2MB buffer. Although
MPEG makes heavy demands on the CPU, most of the demands of
multimedia in CD-ROM today are met by various MPEG add-on boards.
Incidentally, CD-I uses MPEG-1, and Video CD was promoted as the
first MPEG-1 optical disc for multiple platforms.
For the PC multimedia platform, the API for program
interface with MPEG decoders, however, is not standard. The more
used is the OM1 API developed by MCI, adopted by Microsoft, and
by many others as well.
MPEG add-on boards use special chip sets (such as those from
C-Cube Microsystems) for compression and decompression--but there
are various software-only MPEG decoding programs. High-end
hardware solutions claim compression ratios up to 50 to 1--which
is about what is needed to display at 30 fps. But, since MPEG is
lossy, such high rates often signify lower quality playback at 30
fps. At the decoder level, there are three main types of
solutions for the PC platform: overlay, combination boards, and
software-only. Most of them (except the software-only) claim to
provide 30 fps with a Pentium PC.
MPEG-2 (ISO 13818-1, l994) offers higher quality and speeds
than MPEG-1. In certain circles, it is promoted as a step to a
software MPEG solution, because future PCs are expected to have
CPUs capable of processing the coded stream from 500kb/sec to
about 2.0 MB/sec. There are many MPEG-2 hardware solutions (add-
on boards), but the 'software MPEG' products are also making
their mark. British OmniMedia's Software MPEG, for example,
offers a rate of 20 frames/sec with a Pentium 75 PC.
Industry observers comment on the wide use of MPEG-1 outside
of the US, especially in Asia, while the US side, in their view,
seems to be waiting for MPEG-2. In the meantime, many lowcost
proprietary solutions have entered the marketplace. The Open
MPEG Council, a recently formed industry group, hopes to
standardize MPEG in all sectors of the multimedia industry so
that all MPEG-based products will work without problems in the
DOS-Windows platform first, and in other platforms later.
- MSCDEX.EXE
- Known as the Microsoft CD-ROM Extensions, the MSCDEX.EXE
program became necessary when CD-ROM drives were introduced to
the PC platform--and to stop the growth of proprietary extensions
and CD-ROM file managers. With the appropriate CD-ROM device
driver loaded, MSCDEX.EXE enables the PC to configure the drive
(by giving it a drive lettername), and to access the contents of
ISO 9660 CD-ROMs. Other platforms have equivalents to MSCDEX.
The Apple/Mac platform, although it can use HFS and Apple CD-ROM
extensions, it can also use its Foreign File Access to deal with
ISO 9660 CD-ROMs. MSCDEX.EXE is included in MS-DOS and Windows.
See, CD-ROM Extensions
- Multimedia
- This is the new, exciting, and growing arena of applications
that use CD-ROM. Multimedia applications include text, sound,
and motion video in what are mostly new categories of
informational, educational, and entertainment products--and which
have also helped define the new arena of 'infotainment.'
Multimedia uses CD-ROM as its main file storage device. But,
since video files can be very large, multimedia has led to the
growth of specialized software, efficient hardware, and
compression solutions. Some aspects of multimedia are subject to
specifications issued by the Multimedia PC Marketing Council,
currently listed in the MPC Level 2 System Requirements.
Multimedia implementations in CD-I, however, use DYUV for
graphics, MPEG for video, and ADPCM for audio--and display in a
rather low resolution (340x240). IBM also proposed
specifications for multimedia, known as Ultimedia, but they have
not taken hold. In the Mac arena, users have been less hampered
by hardware problems because the Mac comes configured to deal
with CD-ROM and multimedia demands--and some Mac users think
Hypercard is also a satisfactory multimedia authoring tool.
See, Hypercard
- Multi-session
- In optical technology, this refers to a disc that has been
encoded in more than one session. Therefore, the disc has more
than one 'volume'--reason why it is also known as multi-volume.
During recording, the volumes are provided their own Lead-In and
Lead-Out areas. The multi-session disc, however, has a overall
Table of Contents (TOC) that is written at 'closing'--after the
last session is recorded. In some implementations, individual
volumes (sessions) write their tables of contents in their Lead-
in area, and other implementations update the overall TOC. A
multisession drive has to be able to read the contents of all the
volumes in the disc (regular drives can only read the first TOC).
Kodak Photo CD, and CD-ROM-XA and CD-I implement multi-session
features, but only some recent XA drives are truly multi-session
capable. Multi-session specifications were proposed by the
Frankfurt Group, and were initially circulated by the European
Computer Manufacturers' Association as Working Paper TC 15.
See, Frankfurt Group
N
- Non-ISO 9660 CDs
- This category includes CD-ROM products in other proprietary
formats, and as test products for other platforms. There are,
for example, CDs formatted as Apple HFS products. Since mastering
and replication can be done for any format, and new CD-Recordable
hardware is proliferating, non-ISO applications can be produced
in all computer platforms--with the appropriate formatting
software.
- NTSC
- The National Television Standards Committee supports the NTSC
signal and display technology used in the TV industries of North
America, Japan, and a few other countries. It specifies 525
lines/screen, and 29-30 frames/sec.
See, PAL
HDTV
O
- OCR
- In computing circles, Optical Character Recognition involves
scanning hardware and software to produce computer usable text
files from printed pages--as opposed to producing a graphic image
of the page. Essentially, the OCR software recognizes the dot
patterns and produces characters. OCR technology has improved
remarkably, and with more powerful CPUs, it will increase its
reliability and other factors. For documents with complex
layout, uncommon or unclear fonts, and in old or dark color
paper, keystroking is often the best option.
- One-off Discs
- See, CD-Recordable
- Operating Systems
- Generally, an operating system refers to the set of internal
(kernel) and external commands and subroutines that allow the
computer to manage its components. Most operating systems
require (cards or software) interfaces to deal with peripheral
devices (MS-DOS, Mac, OS/2, Unix, etc). CD-ROM drives, and most
other optical devices, are usually packaged with an appropriate
interface card and connecting cable. SCSI CD-ROM drives either
come ready to connect to a 'standard' SCSI-2 card, or come with a
SCSI card of their own--for the appropriate operating system.
Therefore, the same drive can be used in various platforms.
- Optical Byte
- See, EFM
- Optical discs
- Technically, optical discs are those that are 'written'
(encoded) and read using a laser optical device. Some of them
are mastered and mass-reproduced (such as CD-Audio and CD-ROM),
and others are produced individually, by an optical drive
connected to the computer (Write-Once, Rewritable, and
CD-Recordable). The optical industry is clearly divided; with
the mastered and mass-reproduced 12cm CD-ROM implementations in
one camp, and all the other discs in the 'optical' camp. CD-
Audio, obviously, is an industry of its own.
- Optical Recording Technologies
- Although often referred to as encoding, optical recording
technologies are varied and quite sophisticated--the main ones
are summarized below.
For CD-Audio and CD-ROM, which are mass-replicated products,
a glass disk, coated with photoresist, undergoes recording,
development, and a special process to produce the metallized
glass master--which is then used to produce the stampers for the
reproduction equipment. On the desktop, W-O and Rewritable
drives record the optical discs in real time, one at a time. CD-
Recordable drives encode either in Track-at-Once (TAO), or Disc-
at-Once (DAO) mode in the same CD-Recordable media. All those
discs (media) are produced with a recording layer prepared for
the specific recording technology to be applied.
W-O uses Ablative, Phase Transition, Bubble Formation, Alloy
Formation, and Texture Change recording technologies. Ablative
technology, which is the most common, uses a recording layer with
tellurium alloy (low melting point) that allows formation of
holes when the high power laser beam is applied--thus forming
holes or 'pits.' In similar fashion, the other technologies
produce some sort of 'pit' by a phase, color, or texture change.
Rewritable uses Magneto-Optical (M-O), Dye Polymer, and Phase
Change recording technologies. M-O is the most common, and it
uses a magnetic film (of rare earths) for the recording layer, an
appropriate magnetic field, and a high power laser beam to record
or 'rewrite'--applying the Curie and Kerr principles about
changes in structure when heat is applied, and the realignment of
particles (polarization) when a magnetic field is present. Dye
polymer and phase change also use special recording films or
layers, on which the write laser produces the pits. The pits in
these technologies are, however, erasable--they can be reverted
to their original state--therefore the disc can be rewritten.
Some important vendors are adopting phase change technology
(which can erase and write in one pass), and are making it a
serious competitor of M-O technology.
All these recording technologies produce pits that reflect
light with less intensity than the lands about them. The changes
in reflectivity, as the laser passes over them, are detected and
decoded to reproduce the original data.
- Optical Technology
- Technically, optical technology refers to all processes that
involve light, lenses and other devices dealing with transmission
of light (cameras, the eye, microscopes, etc.). In computing
circles, however, optical technology refers to that used in CD-
ROM, Write-Once and Erasable drives. All these devices use high
power lasers to encode the data on the disc, and low power lasers
and photodiodes to read the codes. The 'heads' employed to
'write' and 'read' the code involve sets of precise lenses and
servo-mechanisms that guide the laser beam as well as focus it
with great precision. Obviously, any type of coding that can be
converted to digital code can be transferred to an optical disc.
CD-Audio and CD-ROM are mass reproduced optical products, while
Write-Once, Erasable and CD-Recordable discs are produced
individually. Current optical devices need only appropriate
interface cards to work with computers.
- Orange Book
- The Recordable Compact Disc Standard was published by
Philips, in l990, reportedly in a binder with Orange Covers. The
Orange Book defines two new 12cm CD products: the Magneto-Optical
and the Write-Once.
Part 1, Magneto-Optical (CD-MO), defines tracks that can be
erased and rewritten--reason why this format is more
appropriately known as Rewritable. M-O drives implement magneto-
optical recording technology, on 12cm CDs that are rated to allow
millions of rewrites. These drives are however slower than other
optical drives, because they use two heads--one to erase and the
other to write, in a double-pass process. Some CD-MO products
include a small premastered Read-Only area that usually contains
system and other information--but which can also be read by a
regular CD-ROM drive. The remainder space is the Recordable User
Area, and the user can reuse this area at will. Despite the
original optimism for rewritable M-O drives, they are still not
yet priced low enough to compete with magnetic drives.
Part 2, Write-Once (CD-WO), defines tracks that can be
written to, but not erased and rewritten--in the tradition of
WORM (write-once read-many) discs. A Write-Once drive records
appropriate 12cm CDs--which involve special recording layers,
pregrooved tracks and, generally, a gold reflective layer. The
initial tracks include a Program Calibration Area, are followed
by a Lead-In area (where the Table of Contents will be written),
and by the Program Area--for the user data. The recording
session is finished with the Lead Out. A CD-WO 'Hybrid' disc
involves an area where Read-Only files can be placed, and the
rest of the disc is the W-O area. CD-WO drives remain relatively
high priced, and although the media has reduced in price, CD-WO
is still used mainly in enterprise archival and imaging.
See,
Standards
- OS-9
- This is an operating system, implemented in microcomputers
specifically for CD-I.
- Overhead
- Full-text search and retrieve applications that involve large
collections of text rely mainly on indexing to produce speedy
results. Some database applications with superior functionality
rely heavily on indexing. Indexes, however, can be very large,
averaging between 30 and 50 percent of the textbase, and in some
cases much more. Those indexes are often thought of as overhead,
and provisions must be made for it in the arithmetic of disc
capacity and design.
P
- Packaging
- Once the CD-ROM is produced, it has to be prepared for
distribution. Generally, besides the labelling of the CD-ROM
itself, most replication plants offer printing services for jewel
case inserts, manuals, and other information to fit in or
accompany the jewel case. Once all the items are ready and
assembled as desired, they are either shrinkwrapped or stuffed
into appropriate envelopes or mailers. Some replication plants
even offer mailing services. Obviously, the artwork for the disc
label and insert, the masters for printing, mailing lists, and
all other necessary items must be provided in advance, in the
format specified by the plant. Promoters and sellers try to make
sure authors recognize the role of packaging for the success of
the product, and they have been proved right too often to ignore
their recommendations.
See, Label
- PAL
- Phase Alternation Line, a television standard, is used by
European, Asian and some Latin American Countries. It specifies
768 pixels/line, 576 lines/screen and 25 frames/sec.
See, NTSC
- PCI Local Bus
- The Peripheral Communications Interconnect Local Bus,
introduced by Intel and associated manufacturers (1993), is a
sophisticated local bus--considered superior to the VESA local
bus. It is a 32-bit bus, with a maximum transfer rate of 132
MBytes/sec., that can handle up to ten devices (three of which
can be add-on boards). It is currently used mainly by the
Pentium based PC platform, and it is expected that PCI Local Bus
interfaces for optical devices will be part of the design in
future versions.
- PCM
- Pulse Code Modulation is implemented to structure the analog
signal that is produced by the digital-analog converter of the
CD-Audio player. PCM, therefore, makes it possible to hear the
various instruments, their different ranges and depth of sound,
etc., and is considered the better scheme. It was the basis for
ADPCM, which was implemented in CD-ROM-XA and CDI.
See, ADPCM
- PCMCIA
- The Personal Computer Memory Card International Association
addressed the need for small and portable devices for the growing
portable, notebook and other hand-held computer production lines.
The PCMCIA developed a new interface (with connectors in three
sizes), which essentially senses the device connected, identifies
it, and makes it available to the user. Since the devices
implement PCMCIA electronics, they can be attached to or removed
from the bus at any time.
- Phase-Change Technology
- This rewritable technology employs a recording layer (one of
the special films on the substrate) that shifts phase, from
amorphous to crystalline, when the 'write' laser beam is used.
To erase, a laser beam of higher power heats up the area and,
essentially, melts it--which then cools to the amorphous state
and is therefore ready to be written again. Since phase-change
made possible 'single pass' erasing and rewriting, vendors claim
that their phase-change drives provide faster operation than M-O
drives, and that its slight advantage in storage capacity will
play a bigger role when discs of over one Gigabyte become common.
Some industry magazines claim that it has already reached about
30 percent of the rewritable market, challenging the popular M-O
drives. In 1995, Panasonic introduced a Phase-Change
multifunction drive, at a very competitive price, reflecting the
trends in the Rewritable industry.
- Photo-CD
- See, Kodak Photo-CD
- Physical Format
- Media-specific structure that dictates how the data is laid
out in the disc, data modes, error detection and correction,
physical sector addressing, and other characteristics necessary
to manage the type of data intended for the media.
The volume and file structure for the contents are dealt with by
a logical format.
See, Logical Structure
Red Book
- Pits
- During optical encoding, bursts of a high power (usually a
blue argon) laser beam 'burn' microscopic 'pits' on the recording
layer. The untouched spaces between such pits are called
'lands.' During the read process, the laser light focuses on the
spinning track, and since the pits reflect light less intensely,
the read head detects the changes in reflectivity, and those
changes are processed to produce a binary data stream.
- Pixel
- A Picture Element, used mainly in graphics and video circles,
is the smallest unit of display that can be given color and
intensity values or codes.
- Pre-gap/Post-gap
- These are empty lengths of track (two seconds, or equivalent,
of nothing but 0s), which are placed before and after the data
track.
- Premastering
- Too often, this term is used quite broadly. Data
preparation, indexing, testing (also called simulation), and
creating the 'image' are done before premastering. Premastering
involves taking the 'image' of the application and producing the
premastered file--one large ISO 9660 volume file (a chain of CD-
ROM sectors, with sector addresses, header, synchronization,
error correction and detection, mode, and other required bytes).
The premastered file is further processed for the production of
the glass master. The hardware and software used for premastering
are usually known as 'ISO formatters,' and they vary in
capabilities and features. When using a CD-Recordable drive
premastering takes place as the program records the 'one-
off.'
See, Image
Mastering
- Pressed Discs
- Some circles in the industry use these terms to distinguish
the mass reproduced discs from the rewritable, write-once, and
CD-Recordable discs that are produced one by one, on the desktop.
- Program Area
- This term, introduced in CD-Audio production, refers to the
area of the disc where the user files are stored. The program
area is between the Lead-in and the Lead-out. The user data,
indexes, and other files that go in the program area are placed
in the most appropriate order--to reduce seek and access times.
- Protective Coating
- Optical discs are given a clear plastic or lacquer coat that
protects the metallic layer. Even with this coating, small
scratches, pressure, dirt and other markings can make the disc
unreadable. The coating also prevents air from reaching and
oxidizing the metallized layer--which would render the disc
unreadable.
Q
- QuickTime
- Initially an Apple only product, now found in Windows and
being ported to other platforms, QuickTime is a multifeatured
program that plays sounds, animation, and video files in a time-
based programmed mode--although the display is only about one-
third of the screen (.MOV files). QuickTime movie authoring
involves file compression and on-the-fly decompression. While it
supports Intel's Indeo decompression, the adoption of MPEG
compression/decompression should make it more popular. Some
multimedia products bundle QuickTime, and is found in many
bulletin boards and the Internet.
R
- RAID
- Redundant Array of Inexpensive Disks is a large storage
scheme used increasingly more in large imaging systems, and
industrial multimedia developing systems. The newer RAID systems
offer high reliability and claim (fiber channel) transfer rates
near 100 MBytes per second, and expect to transfer above that
figure soon. RAID's versatility, software and hardware dependent,
includes levels of security, recovery after network or drive
failure, 'hot swapping,' compression and other sophisticated
options.
- RAM
- Random Access Memory, also known as 'system memory,' is that
amount of physical memory that is addressable by and directly
accessible to the CPU--chips on the motherboard, or on an add-on
board on the bus.
- Raw Capacity
- Optical discs include substantial overhead in the encoding,
to work effectively, and to provide the integrity required for
computer data. For any CD-ROM, in percentages, the overhead
includes: the bytes used by the required eight-to-fourteen
modulation (34%), the merging bits (17%), the error detection and
correction codes (11%), and synchronization and subcodes (5%).
This leaves about 33% net space for user data. Efforts to
improve the capacity of optical products are also focusing on
these overhead areas.
- Read Error Rate
- See, BLER
Integrity
- Reed-Solomon Codes
- These are error detection and error correction codes, based
on mathematical algorithms and binary structural logic. The Red
Book implemented the basic two levels of error detection and
correction using Cross Interleaved Reed Solomon Codes (CIRC).
The Yellow Book specified a third level of 'layered' error
detection and error correction codes, to attain the level of
integrity that computer data require. Another scheme of Reed-
Solomon error detection and correction will be used in DVD.
See, Error Detection...
Integrity
- Recording Layer
- This is the sensitive layer, deposited over the substrate,
which reacts in a specific way when a high power laser beam is
focused on it. Each recording technology uses an appropriate
recording layer--which can be Photoresist, a special dye, special
alloy, or a sandwich of sensitive films. For mass-reproduced
CDs, the initial glass disc that is encoded (master) usually has
a Photoresist recording layer.
- Red Book
- Philips and Sony, developers of the CD technology, and of
the 12cm CD, published their specifications for CD-Audio in l980-
-reportedly in a binder with red covers. The Red Book addressed
the physical specifications for the CD; the tracks, the sector
and block layout, coding and sampling of digital audio files, and
other specifications. The Red Book was key for the high quality
sound of CD-Audio, which became a standard and a major world
industry of its own. The International Electrotechnical
Commission published the Red Book as their Doc IEC 908.
See,
Standards
- Reflectivity
- A measurable property of a surface. In optical technology,
baseline reflectivity refers to the reflectivity of the 'lands'--
the clear spaces between the pits in the data track. The pits
have lower than baseline reflectivity. In optical discs, the
changes in reflectivity are detected and decoded, and then
converted to magnetic coding.
- Replication
- In optical technology, replication refers to mass
replication, as in CD-Audio and CD-ROM. Mass replication made
CD-Audio a competitive product. In fact, since the same CD-Audio
mass replication plants produce CD-ROMs, they made possible low
CD-ROM production costs--which were certainly crucial during the
first years of the CD-ROM industry.
- Rewritable Optical Discs
- Rewritable optical technology aims to produce drives that
will replace magnetic storage devices in computers. Vendors
claim that their rewritable optical disks can be erased and
rewritten over a million times. There are three main types of
recording technologies for rewritable optical discs.
Magneto-Optical (M-O) technology is predominant. Phase Change
technology follows far behind, but its adoption by new
manufacturers keeps it in contention. The third is Dye Polymer
technology, adopted by some manufacturers. Until recently,
rewritable discs were mainly 3.5 and 5.25 inches in diameter,
double sided, and of various capacities and proprietary formats.
Currently, the Orange Book 12cm (4.72in) CD-MO appears to be
growing. Recently, Panasonic released a new Phase-Change Drive
that is supposed to read all rewritable (M-O, Phase-change, and
Dye Polymer) discs, PhaseWriter Dual drives claim to read CD-
Audio, CD-ROM and Rewritable discs, and Pinnacle Micro's Apex
Rewritable 4.6 GB drive claims to read CD-ROMs at 16X speed, etc.
See, Encoding Technologies
- RIFF
- Resource Interchange File Format is used to store multimedia
files, because it also allows their use in various platforms.
See, Multimedia
- Rockridge Group
- This is an industry group that developed extensions to the
ISO 9660 to produce ISO-compliant applications that could be
played by multiple operating systems, emphasizing Unix-based or
POSIX-compliant systems. Some saw the need for those extensions,
especially since implementation of ISO 9660 interchange levels
was more problematic than first perceived. The proposed
extensions, System Use Shared Protocol (SUSP), and the Rockridge
Interchange Protocol (RRIP), allow for support of multi-platform
formats, tables of contents with deeper levels of hierarchy, and
the use of filenames larger than those allowed by MS-DOS.
Essentially, those extensions make the ISO-compliant contents of
the disc appear like a Unix File System to Unix machines
configured to support Rockridge Extensions. Incidentally, in a
different approach, there are applications for the Unix platform
that include translation tables to show the contents of the CD-
ROM with Unix-like file and directory names--but that is not what
the Rockridge Group proposal specifies. It was expected that the
Rock Ridge specifications be approved by the end of 1995.
See, Interchange Levels
- ROM
- Read Only Memory. The term originally applied to read-only
memory chips used in computers. With the growth of optical
storage, the term read-only memory now applies to compact disc
products (CD-ROM, CD-I, CD-ROM XA, CD-Recordable, etc.) WORM,
now referred to as Write-Once, after the contents have been
recorded, is also read-only.
See, RAM
- Rotation
- See, Constant Angular Velocity (CAV)...
- Run-Length
- In CD-ROM, run-length specifies the number of contiguous 0s
in the optical byte--between the 1s. This usage is related but
not the same as run-length encoding (RLE), which is a compression
algorithm used widely to compress graphics files.
S
- Sampling
- Sampling is part of analog to digital conversion.
Essentially, the analog signal is sampled at an specific rate and
quantized--which means a numerical value is matched to each
sample, and that value is converted to binary code. Although the
frequency of sampling is important for continuity, the size of
the sample (in bits) is important for depth of quality. CD-Audio
involves sampling rate of 44.1 KHz, and sample size of 16 bits.
- Scanning
- Scanning involves hardware and software. Essentially,
scanners apply a light (laser, and recently LED) to the source
page, so that a set of sensors (charge-coupled devices) can
detect the presence of black areas (or colors) and produce codes
for each pixel, and those codes are processed into raster scan
files. High end scanners, using appropriate chips and hardware,
produce high resolution graphic files. Desktop scanners
popularized the 300 bpi resolution, while fax specifications use
170 bpi resolution. With appropriate software, some scanners can
produce scan files in vector graphics formats. Most scanners,
with appropriate software, can also scan documents for optical
character recognition (OCR). The same principles guide the
specialized scanners such as the hand-held scanners, bar code
readers, slide and microfiche scanners, card scanners, pattern
recognition scanners, and others.
See, OCR
- SCSI
- The Small Computer System Interface was introduced as the
'intelligent interface for intelligent devices.' A SCSI card can
operate in 8 and 16-bit buses, and serve up to seven (or even
more) devices connected in a 'daisy chain'. The interface issues
commands to the chain, where each device recognizes the commands
addressed to it. SCSI hard disks store data in sequential
blocks, and transfer (in parallel) at rates between 3.3 and up to
40 MBytes/sec (the newer implementations offer faster rates).
Nevertheless, despite its many flavors, the fact that SCSI is an
ANSI standard has made for solid commitments to it among some
manufacturers. Currently, SCSI-2 (Fast, Wide, Fast and Wide) are
in use. Ultra SCSI can support up to 15 devices, and is backward
compatible. The SCSI-3 specification, not yet published, is said
to involve asynchronous (serial) mode implementations for fiber
channels, HPSB and other new bus designs in the market.
- Search and Retrieve
- Software operating on large amounts of data (full-text,
databases, spreadsheets, multi-media, etc.) provide search and
retrieve functions to help find the appropriate information
efficiently. Most CD-ROM full-text applications use the now
popular Boolean search and retrieve.
See, Boolean Search
- Sector
- Unlike the sectors and blocks used in regular magnetic
storage devices, the sectors in CD-ROM are prescribed by the
Yellow Book, in the physical format of the data track. The
logical sector, on the other hand, is defined by the ISO 9660,
and is the smallest addressable unit. In technical circles the
difference between physical and logical sectors is clear. But,
in general parlance it is not so clear because, under the ISO
9660, the physical sector (data user area of 2048 bytes) can be
subdivided into Logical Blocks of 512, 1024 or 2048 bytes. And,
since MSCDEX supports only logical blocks of 2048 bytes, each
Mode 1 sector's user data area is one logical block. This usage
has caused many to consider physical and logical blocks as one
and the same.
- Sector Structure
- The sector structures shown here refer to the logical
structures derived from the Yellow Book--the user data areas are
not subdivided into logical blocks. Therefore, the first two
levels of Red Book ED/EC (784 bytes), and the 98 closing control
bytes, are outside the box. In general, it is the size of the
user data area (2048 or more bytes) that is used for the
computations of transfer rates (75 blocks/sec) and the capacities
of the various CD products.
Red Book Specifications (Philips and Sony, 1981)
CD-Audio Sector = 2352 bytes.*
_________________________________________________
| User Data |
| 2352 Bytes |
|_________________________________________________|
Yellow Book Specifications (Philips and Sony, 1983)
CD-ROM, Mode 1 Sector = 2352 bytes.*
_________________________________________________
| Sync Header User Data EDC Blank ECC |
| 12 4 2048 4 8 276 |
|_________________________________________________|
CD-ROM, Mode 2 Sector = 2352 bytes.*
_________________________________________________
| Sync Header User Data |
| 12 4 2336 |
|_________________________________________________|
CD-ROM XA (Extended Architecture).
(All tracks are CD-ROM, Mode 2)
CD-ROM XA Sector, Form 1 = 2352 bytes.*
_________________________________________________
| Sync Header Sub-Header User Data EDC ECC |
| 12 4 8 2048 4 276 |
|_________________________________________________|
CD-ROM XA Sector, Form 2 = 2352 bytes.*
_________________________________________________
| Sync Header Sub-Header User Data EDC |
| 12 4 8 2324 4 |
|_________________________________________________|
Green Book Specifications (Philips and Sony, l986)
(All tracks are CD-ROM, Mode 2)**
CD-I Sector, Form 1 = 2352 bytes.*
_________________________________________________
| Sync Header Sub-Header User Data EDC ECC |
| 12 4 8 2048 4 276 |
|_________________________________________________|
CD-I Sector, Form 2 = 2352 bytes.*
_________________________________________________
| Sync Header Sub-Header User Data EDC |
| 12 4 8 2324 4 |
|_________________________________________________|
Notes.
---------
* There follow the Red Book 1st and 2nd layer EDCs and
ECCs, plus 98 Control Bytes.
** As can be seen CD-ROM XA and CD-I sectors employ the
same structure. Moreover, CD-ROM XA and CD-I tracks are CD-
ROM Mode 2 tracks, where 3rd level EDCs and ECCs are added
only as needed, for interleaved Form 1 tracks that contain
data.
- Servo Mechanisms
- These precise electro-mechanical devices with sophisticated
components are employed for precise shifting of the read (and
write) heads to specific tracks on the disc, to detect variations
in the tracking of the pits and correcting any off-centering, to
position the heads to the appropriate focal length for the laser
as the disc rotates, and so on. The sophistication and precision
of these devices can be appreciated better when one realizes that
the tracks are 1.6 microns wide and that, in the older 1X drives,
the laser is 'reading' pits and lands at a rate of about 75
blocks (150 KB) per second!
- SIGCAT
- The Special Interest Group for CD-ROM Applications and
Technology, based in Reston, VA, is now a non-profit Foundation
dedicated to the promotion of CD-ROM technology in government and
industry. SIGCAT is open to all; it has gained broad government
and corporate support (government policies and CD-ROM
implementation, hardware, software and application developers and
vendors), and has a subscription list of over 9000. DISCourse,
its newsletter, is mailed to all paid subscribed members. The
BLER (Bimonthly Listing of Events and Resources) is mailed to all
who sign up for it. SIGCAT has a Training Center that offers a
varied program of courses and workshops, and its CIRC (CD-ROM
Information Resources Center) serves vendors, software developers
and mostly government users. The yearly SIGCAT National Conference
is becoming a major event in the CD-ROM arena.
- Simulation
- Developers 'simulate' the application, when it is considered
finished, but still in the computer. It involves testing the
software, interface and data, as if it were in the CD-ROM. There
are simulation software packages that can measure retrieval
speeds, output features, screen building, and other features. If
some features are found lacking, they can be improved and
retested until they are satisfactory. Simulations are cost-
effective, because they are performed before the expensive
mastering and replication.
In some CD-Recordable drives, Simulation is a feature that
transfers the data but does not encode the disc--thus simulating
the process. It shows that all is fine, or that the recording is
creating errors or underruns--and saves ruining a clean disc.
- SMPTE
- This is a timing code implemented by the Society of Motion
Picture and Television Engineers. It employs hours, minutes,
seconds, and frames to address the individual frames in a
videotape--a framework not too dissimilar from that of CD-ROM.
To use (NTSC) television signals, which flows at a rate of about
30 frames per second, appropriate SMPTE timing marks must be
included for their use in CD applications.
- Stamper
- A metallic mold (usually nickel) produced by electroforming,
during the mastering process. For small runs, the 'father' (the
first electroformed master) is used in the injection-molding
machine. For large runs, the 'father' is used to produce
intermediate molds and the final stampers that are placed in the
injection-molding machines.
See, Glass Master
Injection Molding
Mastering
- Standards
- Industry standards or specifications for CD-ROM and other CD-
based implementations have common genesis and a historical
relationship, which is summarily displayed by the chart below.
------------------------
---|CD-AUDIO (Red Book,1981)|--------------
| ------------------------ |
Mixed-Mode | |
| -------------------------- |
| |CD-ROM (Yellow Book,1983)*| |
| -------------------------- CD-I
| | | Ready
Mode 1 -------Mode 2 |
| | | |
------------ | -------------------- |
ISO 9660* Non-ISO | | CD-ROM XA | |
| -------------------- |
| | |-- Form 1* |
Bridge Disc** | |-- Form 2 |
(White Book,1993) | |
| | |
----------------------- |
| CD-I (Green Book,1986)|------
-----------------------
|-- Form 1*
|-- Form 2
-----------------------------------
| Orange Book (l990) |
| -Part 1, Magneto-Optical (CD-MO) |
| -Part 2, Write-Once (CD-WO) |
-----------------------------------
* Implements Third Layer of Error Detection and
Error Correction codes.
** Kodak Photo-CD and Video-CD are Bridge Discs.
- Stopwords
- In search and retrieve applications, stopwords are those
words that the application designer wants the search and retrieve
software to ignore altogether. A generic stopword list includes
about 100 common articles, adverbs, adjectives and other
modifiers that are of no use in the logic of a full-text search.
Also, eliminating these common words reduces clutter in the index
tables--which also helps the search process.
- Subcodes
- See, Control Bytes
Channel Bits
- Substrate
- This is the core of the CD. It starts as molten, clear
polycarbonate, for the injection molding machines. After pressing
and cooling, the core disc or substrate is metallized, given a
lacquer protective coating, and labelled. CD-Recordable media
has the same substrate, but different recording layers on it. In
W-O and Rewritable media, the substrate is often glass.
See,
Injection Molding
- Synchronization
- The Synch bytes help the synchronization of the read head
onto the coding in a block (to engage it to begin reading at the
right place). There are 12 synch bytes in a CD-ROM block.
See, Sector Structure
T
- TAR
- Tape Archival and Retrieval format, used extensively during
the reign of the mainframes, served to place files on tapes that
could be retrieved by computers with a different operating
system. Some government information, for example, was sold to
the public in TAR format.
- Termination Resistors
- These small plastic contraptions are placed at both ends of
the chains of devices in a SCSI configuration. Their role is,
essentially, to signal that there are no other devices beyond
that point, and prevent excess signal noise on the SCSI bus.
- TOC
- Table of Contents generally implies a list of the files and
addresses of a CD-ROM application. In current multi-session
applications, each session involves its own table of contents--
and the application scans the disc and begins to read the last
table of contents first. In magnetic drives, since file sizes
can change and be broken into parts, the FAT (file allocation
table) is the system's TOC, because it is an updatable table of
file locations (addresses and distribution) for the entire drive
(logical partition).
- Track
- Optical technology uses Constant Linear Velocity rotation,
which involves a spiral track of coding that begins near the
center of the disc. This track has a pitch of about 1.6 microns
and, in a 63-minute disc, it is about 3 miles long. At another
level, in mixed-mode or multimedia applications, we say that data
types are in 'separate' tracks--but they are in the same physical
track, using appropriate interleaving.
- Track Access
- The common method to access 'songs' by track number in CD-
Digital Audio. Under the Red Book, a disc can have 99 tracks,
and under the Yellow Book, it can have up to 98 tracks of CD-DA
tracks (the first track must be Mode 1 data track). Therefore,
mixed mode discs implement other access methods.
See, A-Time
- Transfer Media
- Initially, mastering plants accepted the image of CD-Audio or
CD-ROM applications in a few specific magnetic transfer media: 9-
track, 1/2in. tapes were the most popular. In time, large
capacity 8mm. Exabyte tapes, 4mm Digital Audio Tapes, and similar
media became acceptable transfer media. Currently, mastering
plants also accept CD-Recordable 'one-offs'.
- Transfer Rate
- The first CD-ROM drives were designed to read 75 blocks of
data per second, which means that 150 KBytes of user data per
second are transferred to the computer's CPU. This basic
transfer rate is now thought of as 1X, because new drives claim
to transfer at multiples of that rate--i.e. 2X, 6X, etc. In
fact, although the current requirement by MPC Level 2 is a
double-spin drive (2X), some multimedia applications recommend
quad-speed (4X) drives. Current literature already mentions 12X
drives.
U
- UDF
- The Universal Disc Format was promoted by the Optical Storage
Technology Association (OSTA), as a single file system for
interchange of information in the computer arena. It was
announced that OSTA will also develop a UDF-based file format for
CD-ROM, write-once and rewritable applications. It is expected
that this universal file format will help eliminate the broad
incompatibility among write-once and rewritable applications, and
with the CD-ROM arena.
- UNIX
- This relatively old and powerful operating system, matured
and spawned various versions in mostly academic, industry, and
government research institutions. Recently, because of the
Internet, the power available on desktop hardware, the growth of
worldwide computer communications, and the efforts to standardize
its code, UNIX is becoming another option on the PC platform.
- User Data
- In CDs, the sectors include an specific space allocated for
data used by the application (user).
See, Sector Structure
V
- VESA
- The industry group, Video Electronic Standards Association,
joined to produce what they termed a non-proprietary response to
IBM's Microchannel architecture. They did so by producing the
VESA Local Bus architecture--known as the VL Bus. It is a 32-bit
bus, with a maximum bandwidth of 132 MBytes per second. It was
designed to aid high speed video devices. The VL Bus Interface
(additional circuitry and chips) extends the CPU bus, and thus
can interact directly with the CPU and memory. However, In the
486 platform, this 32-bit interface was usually limited to only
three VL Bus peripherals--and only two of them could be add-on
boards. The power in the Pentium architecture, and the PCI bus,
have reduced the need for the VESA LB.
- Video CD
- The Video CD specifications ('White Book') were proposed by
JVC and Philips (Aug93), and supported by other major players in
the industry; but it has not been implemented as broadly as first
expected. The CD is used to store 72-74 minutes of full motion
video and digital audio, using an MPEG-1 decompression board, in
a CD-ROM XA 'bridge disc.' (It was, essentially, derived from the
'Karaoke video' concept.) Because CD-I players can play Video CD
discs, it was considered another version of CD-I. Recently,
Panasonic introduced a Video CD player (in various models), and
also announced its promotion of Video CD titles for diverse
markets. Similarly, Philips teamed up with IBM, Apple, Austin and
others, to promote its line of Video CD players and Video CD
titles.
See, Standards
- VL Bus
- See VESA
- Volume
- A volume is defined as a complete CD-ROM. Often, 'ISO
volume' refers to a CD-ROM produced according to the ISO 9660. If
the data, or large files, need to use more than one disc, then
the entire product is known as a Volume Set. We must point out,
however, that under the ISO 9660, Volume Sets can not be produced
under Implementation Level 1. Moreover, multi-volume disc sets
are not supported by MSCDEX.
See, ISO 9660
Implementation Levels
- Volume Descriptor
- The Primary Volume Descriptor is an area of 2 Kbytes, at the
beginning of the track, that includes data and identifiers about
the volume, the publisher, data origination, copyright, dates,
etc.
W
- W-O Technology
- Write-Once Technology, started with WORM (Write Once, Read
Many) computer applications--which involved generally proprietary
formats and hardware options. Philips developed the
specifications for the implementation of Write-Once technology in
the 12cm CD, in the Orange Book, Part 2. Essentially a W-O
drive, with appropriate software, 'writes' the code onto the W-O
disc, in one or more sessions, until the disc is filled. From
then on, the disc is read-only--reason for the 'write-once' name.
Currently, Ablative, Phase Transition, Bubble Formation, Alloy
Formation, and Texture Change technologies are used for recording
W-O discs--ablative technology being the most used. All these
technologies involve a specially designed recording layer, which
undergoes a specific physical change at the spot where the high
power laser beam is focused--forming a 'pit'. As with all
optical technologies, those pits cause changes in reflectivity,
and those changes are decoded to produce the 1s and 0s of the
code stream. Orange Book, W-O applications (12cm CDs), are found
in enterprise document archival, audit trails, scientific record
archival, imaging and imaging archival, and others. Currently,
the growth of multifunction drives (M-O and CD-ROM), and of CD-
Recordable, seems to have slowed the growth of W-O, but it is
still too early to discount Orange Book, W-O technology.
- White Book
- The White Book, produced by JVC and Phillips (l993), used the
sector structure of CD-ROM-XA to produce a Video-CD ("bridge
disc,' or a hybrid CD) that could be played in CD-ROM-XA drives,
and CD-I players as well. Video-CD (which was derived from the
Karaoke CD concept) uses full-motion MPEG. Another implementation
of the White Book is the Kodak Photo-CD.
See, Video CD
Kodak Photo-CD
- WORM
- Stands for Write Once, Read Many, the usage for optical
technology that was applied since the late 70s, in media of
various sizes (5.25in, 12in, and even 14in). Most WORM media was
double-sided, with capacities from 140MBytes to over 3 GB per
side, depending on formats and encoding. The growth of WORM
technology was hampered by the various proprietary hardware and
software solutions, as well as by their price. Nevertheless it
became predominant in archival (imaging) applications, especially
for large enterprises and government agencies. Recently, Orange
Book, Write-Once applications (12cm CD) seem to be slowly
replacing applications in the WORM arena--which was expected.
See, W-O Technology
Y
- Yellow Book
- Published by Philips and Sony, in l983, in a binder with
yellow covers, the 'Yellow Book' used the Red Book as its basis
to detail the physical specifications for the sectors in a
CD-ROM--designed for computer data. The Yellow Book specified
two types of sector layout (Mode 1 and Mode 2), additional
'layered' error detection and correction to insure higher
integrity of the contents, and much more. CD-ROM-XA is defined
in supplements to the Yellow Book. In 1989, the Yellow Book was
issued by the ISO as ISO/IEC 10149, Data Interchange on Read-Only
120mm Optical Discs (CD-ROM).
See, High Sierra Format
ISO 9660
Standards
Leo F. Pozo is a member of the SIGCAT board of directors. He can be reached at leopozo@cpcug.org.
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