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Glossary Audio CD: CD format for audio data Autoloader: A robotic arm to automate the duplicating and or printing process. Authoring: The process of designing and creating the content of a DVD. Blue Book: CD Extra standard created by Phillips & Sony 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 error detection and correction in CDs. An average BLER of less than 220 is considered within the specifications. Buffer A small amount of memory that holds momentarily either instructions or other information, and which is directly available to the CPU. Buffers should not be confused with memory cache. Buffering is 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. Buffer Underrun During recording, a CD-Recordable drive requires data to be provided in an uninterrupted stream at the drive's specified recording rate. If the stream is interrupted for any reason, and the available buffer can not supply sufficient data to cover the interruption, the recording stops and a buffer under run -reporting a buffer underrrun, ending the session, and wasting a blank disc. The Packet Writing option helps reduce buffer underruns. CD: Compact Disc CD Duplication: The process of 'burning' files onto a recordable CD. CD-Extra: a multisession CD comprising of audio and data CD+G: Format used for karaoke CDs CD - I: Compact Disc - Interactive. A multimedia/interactive CD format CD-R: Compact Disc Recordable. A CD which data/audio can be written to once CD Replication: The process of pressing data onto a CD from a master disc. CD-ROM: Compact Disc Read-Only Memory. An optical disc used to store computer data. CD-RW: Compact Disc Re-writable. A CD that can be written with data or audio multiple times. CD Writer/Burner: A drive capable of writing and/or re-writing recordable CDs 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, at a rate of 1.3 m/sec--also called 'reference speed, or scan rate.' CLV requires that the disc spin slower as the head moves to the outer edge of the disc; a CD-ROM, for example, spins from 539 RPM at the inner edge, to 210 RPM at the outer edge. DVDs also use CLV, at a reference speed of 4.0 m/sec. Data Rate: In video applications, this is the quantity of data, usually expressed in megabits per second (Mbits/sec), that the hardware needs to receive either to compress or to display a video clip of a specified quality (bits/pixel), at a specified frame rate and resolution. Should not be confused with hardware transfer rates Data Transfer Rate: Generally, this is the reading speed of the drive. The first CD-ROM drives had a transfer rate of 150 KB/sec. Since then, manufacturers kept multiplying that rate, and are now offering even 12X drives--and even higher speed drives are in the news. DVD specified a raw or minimum transfer rate of about 1.2 GB/sec (equivalent to 8X in CD-ROM). DVD-Video specifies a user data transfer rate of 11.08 Mbits/sec, and a constant Mux_rate of 10.08 Mbits/sec. The difference (1 Mbit/sec) is the system overhead, and is composed of PGCI and DSI codes. Double-layer Discs: The technology was developed by 3M, and enabled 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. The specifications for DVD include double-layer discs, and they should become common when appropriate technical aspects are perfected and available in mastering plants Double Density CD: This was the name for 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 (narrower tracks)in the disc. 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, did not attracte the attention that Philips, Sony, Matshushita, Toshiba and the other major players received for their own proposals--which led to the industry's initial DVD Specifications in late 1995. DVD: Digital Versatile Disc DVD Audio: DVD format designed to store audio data Disk-At-Once (DAO): The process whereby a whole CD is written to without turing the laser off, i.e. there is only a single track burned onto the CD. DVD-5: Single sided, single layer DVD with 4.7 GB of storage DVD-9: Single sided, dual layer DVD with 8.5 GB of storage DVD-18: Double sided, dual layer DVD with 17 GB of storage DVD-R: Digital Versatile Disc Recordable. An optical disc capable of having large amounts of data written onto it once. DVD-RAM: Re-writeable DVD disc. DVD-ROM: Digital Versatile Disc Read-Only Memory. Used for storing computer data. DVD-RW: A re-writable DVD disc. DVD Duplication: The process of 'burning' audio or data onto a recordable DVD. DVD Replication: The process of pressing or stamping data onto a DVD from a master disc. DVD Video: DVD format for storing video data. Encoding: The process of compressing audio or video. 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. Firmware: Instructions and data programmed into the circuits responsible for controlling the operation of peripheral devices, such as CD copiers. Format: To prepare storage media, such as CD or DVD discs for writing. Also, in DVD authoring, often used to describe packaging the DVD Volume directories and files from a layout into a single disc image file, ready to burn to a DVD disc. 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. Green Book: CD-I standard Hybrid CD: CD-ROM standard readable by PCs and MACs . 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 (an erroneous byte in about 5,000 CD-ROMs. In DVD, the use of the Reed-Solomon Product Code is supposed to increase that integrity by a factor of 100. 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 has one with 1478 CDs.). Some implement one or more drives, some include CD-Recordable drives, and most recent products come with software that supports major LAN configurations. In some circles, 'optical jukebox' refers to jukeboxes with WORM and Rewritable optical discs. Master: A disc or file containing data or audio ready for duplication. MPEG: Motion Picture Expert Group. MPEG-1 is the video distribution system used on Video CD & CD-I. MPEG-2 and DVD offer better than laser disc picture quality. 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 circulated by the European Computer Manufacturers' Association as Working Paper TC 15 Packet Writing: This is the newest software that allows CD-Recordable drives to encode entire volumes in a more efficient process (such as reducing buffer underruns)--allowing for multisession, efficient buffering, 'drag and drop,' hybrid discs, and other options. Packet writing software also implements UDF, and is available for most platforms. Packs and Packets In multimedia and DVD, where MPEG compression is implemented, the MPEG audio and video code streams are processed as 'packs' that are coded into sectors (one pack per sector). A pack consists of packets, which are individual streams of code 2048 bytes long (for the up to 8 audio channels, video, VBI streams, system and compression bytes Orange Book: A recorable CD standard; CD-R and photo CD. 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. The initial glass disc or master (for reproducing CD-ROMs) usually has a Photoresist recording layer. Red Book: standard for CD-Rs playable in audio CD players 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. The differences in reflectivity between rewritable and mass reproduced and/or one-off discs can be substantial (15-25% compared to 65-70%). In fact, CD-RW media (Orange Book, III) can not be read by CD-ROM players (without additional hardware fixes). In the same vein, DVD players have wavelength problems with CD-R, because CD-R media does not reflect at all the DVD laser beam. The industry is working to overcome this problem of 'invisibility' in second generation and in multifuntion players. The key promise is that they will be 'multiread Regional Coding: Used in DVD players to only allow DVDs encoded for use in one of the six world regions to be played, as set up by the major motion picture companies. Table of Contents (TOC): Information on the starting positions of tracks in the area of the CD before audio or data Tower: Manual CD or DVD duplicator Track-At-Once (TAO): when the CD is written the laser is turned on and off between tracks, leaving a small gap between audio tracks Track: In DVD authoring, typically used to describe a single sequential piece of material, such as a video clip or slide show, in a DVD project that is then connected by navigational links. A track contains a main video stream plus additional streams, including alternate MultiAngle video, audio, and subtitle streams. A track also can act as a menu, with subpicture button highlights. Video CD: CD format designed to hold video data Wavelength: Laser wavelengths (usually in nanometers) define precision; the shorter the wavelength, the more precise the laser. The infrared laser used in CD-ROM has a wavelength or 780 nm. The red lasers in DVD have wavelengths of 635 and 650 nm (double layer disc). White Book: Video CD standard Yellow Book: CD-ROM standard |
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