A Buyer's Guide to Understanding and Evaluating Optical Storage - Glossary of Terms


Ablative WORM

An optical disk storage technology that uses a laser to alter optical media when writing data. To write, the laser focuses on the disk's metal recording layer with enough heat to create a hole, or pit, in the recording surface.

Access time

The time it takes to access a data track and begin transferring data. In an optical jukebox, it's the time it takes to locate a specific disk, insert it in an optical drive, and begin transferring data to the host system. If the disk is already in the drive, then access time is determined by seek time. Otherwise, it's determined by disk swap time, spin-up time, and seek time.


An electro-mechanical device that moves an object, such as the robotic arm that moves an optical disk within a jukebox, or the device that controls the read/write head on a disk drive.


American National Standards Institute. A standards-setting, independent organization that develops and publishes manufacturing and design standards for the United States.

Archival Management

A storage management solution for cataloging files and moving them to long-term storage, where they can be stored and accessed inexpensively.


A copy of reference data or document images that are stored on optical disks, floppies, tape, paper or microfiche. Typically refers to long-term storage of data for later possible access.


A single-drive, tape-based backup device that houses a number of tape cartridges. An autoloader is designed to support routine, automatic backup procedures, using a mechanical arm to sequentially load a new tape for daily backup.


1. A duplicate copy of a program, disk, or data files. 2. A procedure for duplicating key data files, often automatically, and storing them in a safe place for the purpose of file recovery.

Backward compatibility

A design standard that assures that new software, hardware, devices and media will be compatible with earlier versions. In terms of optical storage, backward compatibility means that existing optical disks will be readable on older optical drives. If backward compatibility is not addressed, archived disks may not be readable on future generations of drives.

Block error rate

The average number of errors that occur (or can occur) while writing or transmitting a block of data.


Temporary storage space within a computer's or device's memory. Most word processors, for example, use a buffer to temporarily store edits as they are being made to a document. When the document is saved, the file is updated and the buffer is cleared.


Compact Disk-Recordable. An optical disk recording format that allows data to be written to optical disks. The disks can be recorded just once, but played virtually without limit.


Compact Disk-Read Only Memory. An optical disk recording format using disks that carry pre-recorded data, music or software. Data cannot be added to or deleted from a CD-ROM.


Compact Disk-Rewritable. An optical disk recording format that allows disks to be recorded and re-recorded, much like floppy disks or audio tapes. The disks can be rewritten up to 10,000 times and played virtually without limit.


Typically a desktop computer hooked up to a network, and designed to work with a more powerful server that runs applications and stores data.


An environment that allows interactions between "clients" (typically desktop computers) and "servers" (computers that store data and run software programs). In client/server environments, data may be stored on a remote server rather than a computer's hard disk; applications may be stored on a server and delivered to individual desktop computers as needed. The server acts as a gateway to the network, running administrative software controls and providing access to the network and its resources.

Computer Output to Laser Disk (COLD)

An optical storage technology for transferring computer-based information to an optical disk for near-online storage. Typically used as an alternative to paper or microfiche-based storage of computer-generated reports.

Constant Angular Velocity (CAV)

The technique whereby data recorded with a variable linear density can be read on a disk with a constant velocity. Despite the varying density of data on the disk, the disk's rotational speed remains constant during reads.

Constant Linear Velocity (CLV)

A storage technique that adjusts the speed of a spinning disk so that the large outer tracks (which normally spin faster) are slowed down during writes, and can thus hold more data than the smaller inner tracks. Typically used in CD-ROM, CLV results in a constant data delivery rate.

Continuous Composite WORM (CCW)

An optical disk storage technology that uses magneto-optical (MO) media to support both rewritable and write-once operations in a single drive. CCW is governed by industry standards that specify multi-layer data protection measures, including procedures for overwrite protection and blank-checking.


Digital Audio Tape. A storage technology that uses 4 mm tape to record data. DAT is similar to an audio tape, but instead of recording data linearly along the length of the tape, data is recorded at an angle. This recording format, called DDS, is the industry standard for all DAT devices.

Data compression

An automatic utility that reduces the size of a data file by removing redundant bits of information. An algorithm built into the hardware, firmware or software handles compression and decompression.

Data migration

See Hierarchical Storage Management (HSM).

Data transfer

The movement of data from one point to another within a computer system, for example, from an optical disk to a computer's hard disk.

Data warehouse

A large centralized database designed to hold and manage a company's information over a long period of time. Data warehouses are often used to mine key data records to detect trends, spot new market opportunities, and monitor business results.


Digital Data Storage. A recording format used by all major DAT drive and media manufacturers, and the only recognized industry standard for DAT systems. A number frequently follows the DDS designation to indicate the generation of the standard: for example, DDS-3 represents a third-generation product.

Disk swap

The act of swapping one optical disk for another. To complete a swap, a jukebox autochanger mechanism must remove a disk from the drive, put it away, retrieve a new disk, and insert it in the drive. The drive then spins-up the new disk and the operation is complete.

Distributed network

A network that divides data processing, storage, and other functions into separate units rather than having them all handled by a single computer.


Digital Linear Tape. A data storage technology that uses half-inch magnetic tape cartridges and longitudinal recording methods to store data.

Document Image Management

A storage management solution for converting paper documents, photos and receipts into an electronic format that can be accessed from a computer.


A software component or set of file commands that allow an application to communicate with another application, driver or hardware device. A driver is what allows a computer to communicate with a disk drive, tape drive or printer, for example.


Digital Video Disk, a disk that closely resembles a standard CD in size, color and physical format, but holds about seven times as much data. A typical CD holds about 650 MB of data, whereas today's DVD-ROM disks hold 4.7 GB, with a target capacity of about 17 GB in the future. A two-hour feature-length movie can fit on a DVD, making it an attractive medium for the entertainment industry as well as PC makers.


DVD-Rewritable. A future technology that will support both playback and recording on DVD. The first capacity point is expected to be 3 GB per disk surface.


DVD-Rewritable. A future technology that will support both playback and recording on DVD.


DVD-Read Only. A DVD format that allows playback but not recording on DVD.

ECC (error correction code)

An embedded code that allows detection of a mismatch between transmitted and received data in a communications system, or between stored and retrieved data in a storage system. The ECC can correct errors, but within limits.


European Computer Manufacturers Association, an international organization founded in 1961 and dedicated to the standardization of information and communication systems.

Effective access time

The actual time it takes to access data. In an optical jukebox, it involves variables such as disk swap time, disk spin-up time, seek time, and transfer rates of the host computer and software application.


A security method in which electronic data is scrambled and decoded using a software or hardware algorithm.

Enterprise network

A system of network connections that links all of a company's LANs, allowing enterprises to communicate across many geographic locations and sites.

Error detection

A software or firmware algorithm that looks for inconsistencies or errors in a data file as it is being stored. More advanced levels of error detection will not only detect problems, but also correct errors or inconsistencies automatically.

Error rate

The ratio of data that is incorrectly recorded or read relative to the entire amount of data written or read. (Note: Error rate is most commonly associated with reading.)

Extended storage

Storage that is added to a computer or system after the purchase, rather than shipped with the system.

File recovery

The process of using backup files to replace lost files after a power failure, facility damage, virus infection, system crash or human error.

Form factor

The physical size of a device or mechanism that is installed in a PC, workstation, jukebox or other system. For example, a 3.5-inch floppy drive has a 3.5-inch form factor. The dominant optical format is 5.25-inch form factor.


The preparation of storage media for recording. Usually involves the complete erasure of existing files, checking for bad sectors, and rewriting the file directory.

Gigabyte (GB)

A unit of measurement for high-capacity data storage. One gigabyte equals approximately one billion bytes, or 1000 megabytes, of information.

Hard disk

A magnetic storage device, usually the primary storage device, for a PC, workstation or server.

Helical Scan Recording (HSR)

Used widely in VHS formats for video recording, the HSR tape recording method writes at an angle across the width of a tape, allowing higher storage densities on half-inch tape.

Hierarchical File System (HFS)

The file management system in which directories have sub-directories and sub-sub-directories. In MS Windows and Macintosh operating systems, the directories and sub-directories are represented as folders nested within other folders.

Hierarchical Storage Management (HSM)

Also known as data storage migration. HSM is a storage management solution where files are moved to the appropriate storage device based on a set of user-defined parameters, including how often the files are used. For example, if a file is not used within a certain period of time, it may be migrated from expensive primary storage to lower cost extended storage, thus reducing storage costs with only minimal impact on accessibility.

Hot swap

The ability to remove and replace a component or device — such as a disk drive, fan or power supply — without turning off the host computer or storage system. Hot swappable components can be replaced "on the fly" with little or no downtime.


International Electronics Commission, founded in 1906 to promote international standards in electrical and electronic engineering.

Industry standards

Rules or guidelines, established by independent consortia, to control the development and manufacture of products and devices in the electronics industry. Industry standards for audio CDs, for example, are what assure consumers that any audio CD will work in any CD player.

Integrated Document Management (IDM)

Combines COLD, data management, workflow and jukebox management into a single integrated application, allowing data users to control a vast amount of information from a single user interface.


The ability to use one brand or type of storage media in a variety of drives. For example, manufacturers of audio tapes and tape players support industry standards for interchangeability, so any tape will work in any player.


International Organization for Standardization, a worldwide organization that develops, publishes and promotes international industrial and technical standards. The term ISO is not an acronym, but a derivative of the Greek word isos, which means "equal."


A standalone cabinet that holds multiple optical disk drives and cartridges for high-speed, high-capacity storage. It includes a robotic arm to pick an optical cartridge from its storage slot, move it to one of several drives, then return it to the slot when it is no longer needed. Sometimes called an optical disk library.

Kilobyte (KB)

Approximately one thousand (actually 1,024) bytes.


Local Area Network. A communications network used to connect computers and other electronic devices within a confined geographical area. For example, a LAN can connect users within a single site, allowing them to share data, exchange e-mail, and share peripherals.


Light Intensity Modulation Direct Overdrive. An optical recording technology that allows write procedures to be accomplished in one pass of the optical read/write head over the media. LIMDOW accelerates optical performance, but requires somewhat complex and expensive optical media, and involves a more complicated write procedure that leaves less margin for error compared with other optical technologies.

Live trial software

Fully functioning evaluation software that can be installed and used prior to purchase.


A removable chamber that holds multiple optical disk cartridges or magnetic tapes, often used for high-volume automated backup.

Magneto-Optical (MO)

An optical disk storage technology that uses a magnet and laser to alter the magnetic flux directions on a disk's recording surface, much like the operation of a magnetic hard disk. The laser heats a small point just above the disks' recording surface. Above a certain temperature, the disk's recording surface can be altered with a magnet, causing a change in reflectivity that is detected during reads. MO is the dominant technology for rewritable optical disks, and meets ANSI, ISO and ECMA industry standards for interchangeable optical disk cartridges.

Mean swaps between failure (MSBF)

A measure of reliability specific to optical jukeboxes, usually determined in benchmark testing. MSBF refers to the average number of disk "swaps" a jukebox and its internal mechanisms can be expected to deliver before maintenance is required.

Mean time between failure (MTBF)

A measure of reliability for electronic equipment, usually determined in benchmark testing. The higher the MTBF, the more reliable the equipment.

Mean time to repair (MTTR)

A measure of the complexity of design in electronic equipment. Highly modular designs — i.e., those that use interchangeable, hot-swappable components — typically have a low MTTR since failed components can be replaced with functioning components.


A physical storage medium. Includes optical disks, CDs, magnetic tapes, hard disks, and other technologies used to store computer-based information.

Megabyte (MB)

A unit of measurement for data storage. One megabyte equals approximately one million bytes of information.

Megabytes per hour/second

Units of measure that describe the speed at which data is transferred from one device to another, for example, from an optical disk to a computer's hard disk. Often abbreviated to MB/h and MB/s.

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Francis Bacon