GLOSSARY OF CD-ROM TECHNOLOGY

By, Leo F. Pozo*
(Copyright, 1994, 1995, 1996) 





  
About this Glossary

    
See, Author

  
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. 

  
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

  
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. 

  
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.

  
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.

  
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.   

  
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. 

  
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.

  
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

  
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

  
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

  
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

  
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

  
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

  
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. 

  
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. 

  
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.

  
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.

  
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

  
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.

  
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

  
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-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

  
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

  
Author

    
* Leo F. Pozo is a Member of the SIGCAT Board of Directors. For more information
on this copyrighted Glossary or other related published material, please write to:

    
        



         Leo F. Pozo
         2801 Fort Drive
         Alexandria, VA 22303-1324.  
         Telephones:  (W) 703-325-6146, and (H) 703-329-7873. 





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