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Access time The time required by a CD-ROM drive to read the data requested from the CD-ROM disc and send it back to the computer.
ADPCM Adaptive Different Pulse Code Modulation is a method of compressed audio data storage in which it is not the value of the signal which is stored but the difference from the previous sample (or measurement). This means that only 4 bits are needed per sample rather than the normal 16 bits. In the CD-i standard, the levels A, B and C are recognized. B and C are also used in CD-ROM XA. The sample frequencies used to measure the audio signal are 37.8 KHz and 18.9 KHz for B and C respectively. This brings the band width (the maximum frequency to be reproduced) to 17 and 8.5 KHz. For level A, these figures are 44.1 KHz 20 KHz. Using ADPCM, a maximum 16 - fold reduction in storage requirements can achieved (Level C, mono).
AMS Automatic Mastering and Stamper making System.
ATRAC Adaptive Transform Acoustic Coding A method of compression of audio signals as used for Mini Disc.
BER Bit Error Rate: expressed as the number of correctly processed bits before a erroneous bit is detected. For CD-ROM the figure is 10 to the power 12.
BLER Block Error Rate; expressed as the number of blocks with at least I error against the total number of blocks measured.
Block In CD-ROM technology the data is stored on the CD-ROM in blocks, sometimes called sectors or frames, of 2 KBte (2048 Bytes). Apart from the user-data, extra information is added (see: Mode 1/2, Form 1/2).
Byte A symbol or character, consisting of 8 bits.
Caching The mechanism by which a cache is used to store recently reque- sted information. On the next request for the same information, the system retrieves it from fast cache- memory rather than from the slower medium.
CD Bridge disc The CD bridge disc is a special type of CD-ROM XA disc with a CD-i application program. By using the CD Bridge disc concept, the discs can be played on a variety of players such as CD-i, CDROM XA, etc. Examples are Photo CD and Video CD.
CD-i Compact Disc Interactive; a system for presenting information (text, image and video) on a television screen. The standard is defined by Philips and Sony and contained in the Green Book.
CD-ROM Compact Disc Read Only Memory; a storange medium which can only be read, based on audio CD technology. Maximum capacity: for 74 minutes: 681984000 Bytes = 650 MByte for 63 minutes: 580608000 Bytes = 553 MByte where I minute = 60 seconds; I second 75 frames; I frame = 2048 Bytes.
CD-ROM XA XA stands for eXtended Architecture and is a standard for CD-ROM in which a number of options from CD-i have been added. These include audio compression (ADPCM), multi-channel audio (max. 16), file interleaving, user data (2336 Bytes/ sector), image compression capability, etc. A CD-ROM XA disc is a Mode 2 disc, in which the data is located in Form 1 (2048 Bytes/sector) or Form 2 (2336 Bytes/sector) sectors.
DAT Digital Audio Tape, a 4 mm tape format also used for data storage.
Data Capture Method of converting data from non-electronic data carriers (paper, microfiche, artwork, etc.) into a form which allows processing by computer.
Data Compression A technique in which as much superfluous information as possible is removed from the data. Example: a repeating sequence can also be stored as the value and the number of repetitions.
DCC Digital Compact Cassette. The DCC system is an extension of the existing Compact Cassette standard, defining a magnetic tape system that includes recording and playback of digital data.
Directory A file that contains information (name and location) about the files on a disk. Used in almost every storage medium (floppy, hard disk, CD-ROM).
EDC Error Detection Code; a checksum of the previous Bytes in the sector. This enables the, CD-ROM player to conclude immediately that a (read) error has occurred during the reading of the information. With the use of ECC, errors of this kind can be corrected to a certain extent.
Floppy disk Removable magnetic medium in a synthetic jacket. Information can be stored on it using a read/write head. The information is erasable.
FMV Full motion, full screen video.
Form 1 Used in CD-ROM. Division of the Mode 2 sector intoSync (12 Bytes). Header (4 Bytes), Subheader (8 Bytes), User data (2048 Bytes), EDC (4 Bytes), ECC (276 Bytes). This layout is used for normal data files (incl. Photo CD and Electronic Book).
Form 2 Used in CD-ROM. Division of the Mode 2 sector into Sync (12 Bytes). Header (4 Bytes), Subheader (8 Bytes), User data area (2324 Bytes) and 4 Bytes reserved or 4 Bytes for EDC. This layout is used for files where error correction is pointless or impossible due to their real-time character such as compressed audio or moving images.
GB GigaByte, 1024 MB = 1024 x 1024 1024 = 1,073,741,824 Bytes.
GB GigaByte, 1024 MB.
Hard disk The hard disk is a permanent, (fixed) storage medium for computer data based on a rotating disc with a magnetically, sensitive layer. Information can be written on this and read again using a read/write head. The information stored is erasable.
HFS Hierarchical Filing System, used by, Apple. Used for floppy and hard disks and for CD-ROM. Apple also supports the ISO 9660 standard.
Injection Moulding The process in which polycarbonate is sprayed under pres sure against the stamper to produce the CD After moulding, an aluminium layer is added to the surface and then lacquered.
Interactive Media Media in which the user is required/expected to take action to find information or in order to be provided with information.
Interface The point of contact or border surface between two systems. These can be items of equipment (e.g. SCSI interface between computer and CD-ROM player) software modules (user interface).
JPEG A compression algorithm defined by: the joint Photographic Expert Group for continuous tone images (colour pictures Permitting loss of information non-essential for human observation, compression rates 10-30:1 can be achieved. "Loss less" compression cannot go beyond 8: 1.
Karaoke Japanese word for "empty orchestra". A form of entertainment where guests in a Karaoke bar can take the microphone and start singing.
KB KiloByte, 1024 Bytes.
MB MegaByte, 1024 KB.