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Technology Definitions
This field records the name of a file stored in the root directory, which describes the contents of the disc. Maximum: 8+3 d-characters, use optional.
Advanced Intelligent Tape (AIT) was designed to provide a combination of data integrity, speed and high capacity. Made of strong, thin, media it incorporates a unique Memory-In-Cassette (MIC) feature.
Records the name of a particular application needed to access the data on the disc, if any. Maximum 128 a-characters allowed, use optional.
This field stores the name of a file (which may be recorded in any directory) containing bibliographic information such as an ISBN number. Maximum: 8+3 d-characters, use optional.
To record information onto a writable optical medium such as a CD-R, CD-RW or DVD+RW.
Authors can protect their work with a copyright notice stored in a file, which must be placed in the root directory. The name of this file may be recorded in the Copyright File Name Volume Descriptor. Maximum: 8+3 d-characters, use optional.
A recordable CD technology for data and music storage using a low-cost disc that can be written only once. This technology uses an organic dye, so is not considered ideal for long term data storage. To record a 650MB disc takes from 5 to 74 minutes depending on the speed of the drive. CDR drives and media can also support UDF and don't have to record in track at once or disc at one modes.
A compact disc format used to hold text, graphics and hi-fi stereo sound. The audio CD player cannot play CD-ROMs, but CD-ROM players can play audio discs.
A rewritable CD technology. CD-RW drives can also be used to write CD-R discs, and they can read CD-ROMs. A CD-RW disc can be rewritten over a thousand times and read on MultiRead CD-ROM drives or CD-RW compatible Audio CD players. CD-RWs support UDF (Universal Disc Format), which means they are designed for read-write interoperability between all the major operating systems as well as compatibility between rewritable and write-once media. Today, both high-speed and current speed CD-RW are available.
Records the name of author of the content of the disc. Maximum 128 a-characters allowed, use optional.
There is a Volume Descriptor field for each of four dates (Creation, Modification, Expiration, Effective), in the format: year, month, day; hour, minute, second. All these fields are optional.
A method of writing CDs in which one or more tracks are written in a single operation, and the disc is closed, without ever turning off the writing laser. Contrast with Track-at-Once. Not all CDrecorders support Disc-at-Once.
A single large file which is an exact representation of the whole set of data and programs as it will appear on a CD, in terms of both content and logical format. This may be an ISO 9660 image (adhering strictly to the ISO 9660 standard), or some proprietary format.
Digital Linear Tape dates back to the mid-1980s and is based on standard half-inch magnetic tape. Effectively, DLT is an adaptation of the old reel-to-reel magnetic recording method where the tape cartridge performs as one reel and the tape drive as the other. DLT drives use half-inch wide metal particle tape onto which data is recorded in a serpentine pattern on parallel tracks grouped into pairs. Each data track goes the entire length of the tape. When data is recorded, the first set of tracks is recorded on the whole length of the tape. When the end of the tape is reached, the heads are repositioned to record a new set of tracks, and the tape is again recorded on its whole length, this time in the opposite direction. The process continues, back and forth, until the tape is full. Current drives record either 128 or 208 tracks. The higher density is achieved by angling the data pattern on adjacent tracks using a technique called Symmetric Phase Recording (SPR). SPR's herringbone pattern eliminates the need for guard bands, thereby allowing greater track density.
Launched in mid-2000, this audio-only storage format similar to CD-Audio, however offers 16, 20 and 24-bit samples at a variety of sampling rates from 44.1 to 192KHz, compared to 16 bits and 44.1KHz for CDs. DVD-Audio discs can also contain music videos, graphics and other information.
Introduced in 1996, the optical discs share the same overall dimensions of a CD, but have significantly higher capacities - holding from 4 to 28 times as much data.
An international association of hardware and media manufacturers, software firms and other users of Digital Versatile Discs, created for the purpose of exchanging and disseminating ideas and information about the DVD Format. The DVD Forum is working to promote the broad acceptance of DVD-RAM as a rewritable standard for DVD in IT industries and DVD+RW in the entertainment and consumer electronics industries. DVD Forum support is not necessary to win in the marketplace.
DVD Multi is a logo program that promotes compatibility with DVD-RAM and DVD-RW. It is not a drive, but defines a testing methodology which, when passed, ensures the drive product can in fact read RAM and -RW. It puts the emphasis for compatibility on the reader, not the writer. The read-write specification was introduced in June by the DVD Forum in response to compatibility issues with DVD-RAM. It will be able to read discs written in DVD-ROM, DVD-Video, DVD-Audio, DVD-RW and DVD-R formats. It will be able to write discs in DVD-RAM, DVD-RW and DVD-R formats. So far, no optical drive manufacturer has announced plans to support the specification.
Popular format for high quality MPEG2 video and digital surround sound. Enables multilanguage, multisubtitling and other advanced user features.
The authoring use drive (635nm laser) was introduced in 1998 by Pioneer, and the general use format (650nm laser) was authorized by DVD Forum in 2000. DVD-R offers a write-once, read-many storage format akin to CD-R and is used to master DVD-Video and DVD-ROM discs.
A rewritable DVD disc endorsed by Panasonic, Hitachi and Toshiba. It is a cartridge-based, and more recently, bare disc technology for data recording and playback. DVD-RAM bare discs are fragile and do not guarantee data integrity. The first DVD-RAM drives were introduced in spring 1998 and had a capacity of 2.6GB (single sided) or 5.2GB (double sided). DVD-RAM Version 2 discs with 4.7GB arrived in late 1999, and double-sided 9.4GB discs in 2000. DVD-RAM drives typically read DVD-Video, DVD-ROM and CD media. The current installed base of DVD-ROM drives and DVD-Video players cannot read DVD-RAM media.
First introduced in 1997, this read-only DVD disc is used for storing data and interactive sequences as well as audio and video. DVD-ROMs run in DVD-ROM or DVD-RAM drives, not DVD-Video players connected to TVs and home theatres. However, most DVD-ROM drives will play DVD-Video movies.
A rewritable DVD format, introduced by Pioneer, that is similar to DVD+RW, but its capability to work as a random access device is not as good as +RW. It has a read-write capacity of 4.7 GB.
Developed in cooperation by Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha, it is the only rewritable format that provides full, non-cartridge, compatibility with existing DVD-Video players and DVD-ROM drives for both real-time video recording and random data recording across PC and entertainment applications.
The standard logical format for CD-ROM originally proposed by the High Sierra Group, on which the ISO 9660 standard is based; essentially identical to ISO 9660. The original High Sierra format is no longer used.
The most common international standard for the logical format for files and directories on a CD-ROM. Some other common logical formats such as Joliet and Rock Ridge are extensions of ISO 9660.
Methods of recording and naming files on disc under the ISO 9660 standard. There are three nested, downward-compatible Levels.
In Level 1 (the lowest common denominator, developed with DOS file naming limitations in mind):
- Each file must be written on disc as a single, continuous stream of bytes -- files may not be fragmented or interleaved.
- A filename may not contain more than eight d-characters.
- A Filename Extension may not contain more than three d-characters.
- A directory name may not contain more than eight d-characters.
In Level 2, again, each file must be written on disc as a single, continuous stream of bytes, but there are no restrictions on filenames.
In Level 3 there are no restrictions at all. This allows for writing files in multiple extents, so it is used for packet writing.
Joliet is an extension of the ISO 9660 standard, developed by Microsoft to allow CDs to be recorded using long filenames, and using the Unicode international character set. Joliet allows you to use filenames up to 64 characters in length, including spaces.
The term used for a mechanical library device for storing multiple pieces of media for mass near-line storage, as the name suggests, it is similar to a music jukebox to play records/CD’s.
An area at the beginning of each session on a recordable compact disc, which is left blank for the session's Table of Contents. The lead-in is written when a session is closed, and takes up 4500 sectors on disc (1 minute, or roughly 9 megabytes). The lead-in also contains next writeable address on the disc, so that future sessions can be added (unless the disc is closed).
An area at the end of a session, which indicates that the end of the data has been reached. The first lead-out on a disc is 6750 sectors (1.5 minutes, about 13 megabytes) long; any subsequent lead-outs are 2250 sectors (.5 minute, about 4 megabytes).
Light Intensity Modulated Direct OverWrite technology uses a different write technology, which was intended to improve on the performance levels of earlier MO devices.
LIMDOW disks and drives work on the same basic principle as a standard MO drive: the write surface is heated up and takes on a magnetic force applied from outside. But instead of using a magnetic head in the drive to make the changes, the magnets are built into the disk itself.
The LIMDOW disk has two magnetic layers just behind the reflective writing surface. This write surface is even more clever than MO as it can take magnetism from one of those magnetic layers when it has been heated up to one temperature; but if it has been heated up further, it will take its polarity from the other magnetic layer. To write the data onto the disk, the MO drive's laser pulses between two powers.
At high power, the surface heats up more and takes its magnetic "charge" from the North Pole magnetic layer. At the lower power, it heats up less and takes its magnetic charge from the South Pole layer. Thus, with LIMDOW the MO write process is a single-stage.
Linear Tape Open (LTO) is, as the name implies, an attempt to develop an open standard for linear tape storage as an alternative to the proprietary Quantum DLT format. Proposed and developed initially by a consortium of Hewlett-Packard, IBM and Seagate, LTO technology combines the advantages of linear multi-channel, bi-directional formats with enhancements in servo technology, data compression, track layout and error correction code to maximise capacity, performance and reliability.
There are two formats based on the LTO technology:
- The Accelis format is designed for applications that require exceptionally fast access times, such as on-line data inquiry and retrieval. Tape devices based on the Accelis format are expected to provide access times under 7 seconds, capacities of up to 400GB compressed (80MBps to 160MBps native)
- Ultrium is a single-reel format targeted at users requiring ultra-high capacity backup, restore and archive capabilities. The Ultrium format enables manufactures to develop products with up to to 200GB of compressed capacity and deliver transfer rates from 20-40MB per second compressed (10 to 20MB per second). Ultrium products deliver cartridges of varying capacities from 20GB compressed (10 native) to 200GB compressed (100GB native). Ultimately, compressed capacities are expected to rise to 1.6TB (800GB native) on a single cartridge and transfer rates to between 160-320MBps compressed (80MBps to 160MBps native).
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As implied by the name, this technology uses a hybrid of magnetic and optical technologies, employing a laser to read data on the disk, while additionally needing magnetic field to write data. An MO disk drive is so designed that an inserted disk will be exposed to a magnet on the label side and to the light (laser beam) on the opposite side. The disks, which come in 3.5in and 5.25in formats, have a special alloy layer that has the property of reflecting laser light at slightly different angles depending on which way it's magnetised, and data can be stored on it as north and south magnetic spots, just like on a hard disk.
While a hard disk can be magnetised at any temperature, the magnetic coating used on MO media is designed to be extremely stable at room temperature, making the data unchangeable unless the disc is heated to above a temperature level called the Curie point, usually around 200 degrees centigrade. Instead of heating the whole disc, MO drives use a laser to target and heat specific regions of magnetic particles. This accurate technique enables MO media to pack in a lot more information than other magnetic devices. Once heated the magnetic particles can easily have their direction changed by a magnetic field generated by the read/write head.
Information is read using a less powerful laser, making use of the Kerr Effect, where the polarity of the reflected light is altered depending on the orientation of the magnetic particles. Where the laser/magnetic head hasn't touched the disk, the spot represents a "0", and the spots where the disk has been heated up and magnetically written will be seen as data "1s".
MO disks can offer very high capacity and fairly cheap media as well as top archival properties, often being rated with an average life of 30 years - far longer than any magnetic media.
Optical File System, a FileSytem format used by QStar Technologies supporting Optical technology in all available sector sizes. The major standard form factors of Optical are supported, including 12” WORM, 5 1&Mac218;” rewritable and WORM.
To write on the fly means to write directly from source data to CD data without first writing a disc image.
Optical Super Density (OSD) technology's design goals were to develop a high capacity (40GB or more) removable MO drive which retained the ruggedness and reliability offered by today's ISO-standard MO solutions, achieve data transfer rates competitive with hard disk and tape products (30 MBps) and provided the user a significantly lower cost per megabyte than other optical and tape products.
This association is composed of major optical drive manufacturers. Its purpose is to endorse standards and promote the use of optical media.
An optical storage technology in which the disk drive writes data with a laser that changes dots on the disk between amorphous and crystalline states. An optical head reads data by detecting the difference in reflected light from amorphous and crystalline dots. When full a phase-change disk can be erased (or "reformatted") using a medium-intensity pulse to restore the original crystalline structure. CD-RW, DVD-RAM and some earlier optical drives use phase-change technology.
Identifies the publisher of the disc. Maximum 128 a-characters allowed, use is optional.
An extension of the ISO 9660 file system designed to support UNIX file system information (such as longer filenames and deeper directory structures).
Small Computer System Interface (pronounced "scuzzy"). An interface, which allows up to seven peripheral devices to be linked to a single controller, or fifteen on a Wide controller. SCSI comes in three main standards:
- • Single Ended (S/E) - usually restricted to 3 metres total bus length
- • Low Voltage Differential (LVD) - up to 12 metres total bus length
- • High Voltage Differential (HVD) - up to 25 metres total bus length
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Different device bus types should not be connected on the same bus (devices must all be S/E, LVD, or HVD and not a combination). Most libraries only support the narrow seven devices SCSI.
Standard Data Format, a FileSytem format used by QStar Technologies that supports DVD-RAM, Optical with sector sizes of 512, 1024, 2048 and 4096, as well as DLT, LTO and AIT tape technology. It has support for file spanning and has a self-describing filesystem on the media, allowing fast disaster recovery.
As defined in the Orange Book, a recorded segment of a compact disc, which may contain one or more tracks of any type (data or audio). In data recording, there is usually only one track per session. In audio recording, all audio tracks are contained in a single session. A lead-in and lead-out are recorded for every session on a disc.
Session-at-Once is a subset of Disc-at-Once, used for CD Extra. In Session-at-Once recording, a first session containing multiple audio tracks is recorded in a single pass, then the laser is turned off, but the disc is not closed. Then a second (data) session is written and closed.
The operating system under which the application will run. This Volume Descriptor may contain a maximum of 32 a-characters, and its use is optional.
For a whole disc or any session within a disc, shows the number of tracks, their starting locations, and the total length of the data area. The TOC does NOT show the length of each track, only.
A method of writing data to disc. Each time a track (data or audio) is completed, the recording laser is stopped, even if another track will be written immediately afterwards. Link and run blocks are written when the laser is turned on and off.
Universal Disc Format. A file system endorsed by OSTA (the Optical Storage Technology Association) for use with packet writing and other recordable optical disc technologies, such as DVD.
Ultra Density Optical (UDO) utilizes blue-violet laser and phase change media recording technology from DVD consumer products. First generation UDO products are expected to be 30GB capacity and are scheduled to ship in 3rd quarter 2003. Future generations will increase capacity to 60GB and 120GB and will provide full backward read compatibility. Both WORM and rewritable media will be available and the cartridge will be physically identical to 5.25" MO to maintain library compatibility. |
For an ISO 9660 disc, the Volume Descriptors are a set of optional information fields recorded at the beginning of the data area on the disc. They were originally designed for the needs of CD-ROM publishers. The full set of Volume Descriptors is as follows:
This is the disc name, which is displayed by your operating system when the disc is mounted. It may contain a maximum of 32 a-characters, and its use is recommended.
If the CD you are preparing is part of a set of discs, every disc in the set may have an identical Volume Set Name, recorded in this field. The Volume Set Name may contain a maximum of 32 d-characters, and its use is optional.
Write Once Read Many, data can only be written to blocks once on the media, but cannot then be altered at a block level. The data is then available to be read as often as is required.
A feature used by most Optical manufacturers, this allows data to be verified after a write at a block level, if the data does not verify, it is re-written. For optical drives that do not support this feature, QStar Technologies apply this at a software driver level to ensure data integrity. Most hardware manufacturers that support this feature allow it to be disabled, however, this is not recommended, as although it may improve performance, it may compromise data integrity.
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