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actuator: A mechanical assembly that positions the read/write head assembly over the appropriate tracks.

AIN: advanced intelligent network; a service-independent telecommunications network in which the intelligence is moved from the switch and hosted in computer nodes distributed throughout the network.

AIT: advanced intelligent tape; a helical scan technology developed by Sony for tape backup/archive of networks and servers, specifically addressing midrange to high-end backup requirements.

array: an arrangement of two or more disk drives: may be in RAID or daisy-chain fashion.

ATM: asynchronous transfer mode; a network architecture that divides messages into fixed-size units (cells) and establishes a switched connection between the originating and receiving stations; enables transmission of various types of data (video, audio, etc.) over the same line without one data type dominating the transmission.

backbone: the underlying network communication conduit or line by which all main servers and devices are connected; backbone devices are typically servers, routers, hubs, and bridges; client computers are not connected directly to the backbone.

bandwidth: the amount of data that can be transmitted via a given communications channel (e.g., between a hard drive and the host PC) in a given unit of time.

block: a portion of a volume usually 512 bytes in size; often referred to as a "logical block."

burst mode: a temporary, high-speed data transfer mode that can transfer data at significantly higher rates than would normally be achieved with non-burst technology; the maximum throughput a device is capable of transferring data.

bus: the main communication avenue in a computer; an electrical pathway along which signals are sent from one part of the computer to another.

byte: the fundamental data unit for personal computers, comprising 8 contiguous bits.

Cache: a large bank of random access memory used for temporary storage of information.

CAD: computer-aided design; the use of a computer in industrial design applications such as architecture, engineering, and manufacturing.

Central Office: a secure, self-contained telecommunications equipment building that houses servers, storage systems, switching equipment, emergency power systems, and related devices that are used to run telephone systems.

clustered servers: the concept of combining multiple host computers together through a private communication line, such as Ethernet backbone, to form a ring of host computers; this ring of host computers act as a single entity, capable of performing multiple complex instructions by distributing the workload across all members of the ring.

clustered storage: the concept of combining multiple storage servers together to form a redundant ring of storage devices; clustered storage systems typically perform multiple read and write requests through parallel access lines to the requesting computer.

commerce service provider (CSP): a company that provides e-commerce solutions for retailers.

competitive local exchange carrier (CLEC): a long distance carrier, cable company, or small startup local exchange carrier that competes for business in a local telephone market; many CLECs also offer Internet services.

controller: a unit or circuitry that manages the information flow between storage disks and the computer.

cost of ownership: the purchase price of equipment plus the cost of operating this equipment over its projected life span.

COTS: commercial off-the-shelf; commercially available products that can be purchased and integrated with little or no customization, thus facilitating customer infrastructure expansion and reducing costs.

CTI: computer telephony integration; providing a link between telephone systems and computers to facilitate incoming and outgoing call handling and control; the physical link between a telephone and server.

DAT: digital audio tape; a digital magnetic tape format originally developed for audio recording and now used for computer backup tape; the latest DAT storage format is DDS (digital data storage).

disk array (or array): an arrangement of two or more hard disks, in RAID or daisy-chain configuration, organized to improve speed and provide protection of data against loss.

distributed computing environment: a set of middleware standards that defines the method of communication between clients and servers in a cross-platform computing environment; enables a client program to initiate a request that can be processed by a program written in a different computer language and housed on a different computer platform.

DLT: digital linear tape; a serpentine technology first introduced by Digital Equipment Corporation and later developed by Quantum for tape backup/archive of networks and servers; DLT technology addresses midrange to high-end tape backup requirements.

EIA: Electronic Industries Association; a trade association that establishes electrical and electronics-oriented standards.

EMI: electromagnetic interference; what occurs when electromagnetic fields from one device interfere with the operation of some other device.

enterprise storage network (ESN): an integrated suite of products and services designed to maximize heterogeneous connectivity and management of enterprise storage devices and servers; a dedicated, high-speed network connected to the enterprise's storage systems, enabling files and data to be transferred between storage devices and client mainframes and servers.

Ethernet: a local area network standard for hardware, communication, and cabling.

failover: the transfer of operation from a failed component (e.g., controller, disk drive) to a similar, redundant component to ensure uninterrupted data flow and operability.

fault tolerance: the ability of a system to cope with internal hardware problems (e.g., a disk drive failure) and still continue to operate with minimal impact, such as by bringing a backup system online.

FC-AL: Fibre Channel-Arbitrated Loop; a Fibre Channel implementation in which users are attached to a network via a one-way ring (loop) cabling scheme.

Fibre Channel: a high-speed storage/networking interface that offers higher performance, greater capacity and cabling distance, increased system configuration flexibility and scalability, and simplified cabling.

footprint: the amount of floor space that a piece of equipment (e.g., a rackmount enclosure) occupies.

form factor: the physical size and shape of a device; often used to describe the size of disk arrays in a rackmount enclosure.

gigabyte: approximately one billion bytes, 1,024 megabytes.

HBA: host bus adapter; a hardware card that resides on the PC bus and provides an interface connection between a SCSI device (such as a hard drive) and the host PC.

home page: the main page on a Web site that serves as the primary point of entry to related pages within the site and may have links to other sites as well.

host-attached storage: a storage system that is connected directly to the network server; also referred to as server-attached storage.

hot spare: a backup component (e.g., disk or controller) that is online and available should the primary component go down.

hot swappable: the ability to replace a component (e.g., disk drive, controller, fan, power source) while the system is on line, without having to power down; also referred to as hot-plug removable.

HSM: hierarchical storage management; a storage system in which new, frequently used data is stored on the fastest, most accessible (and generally more expensive) media (e.g., RAID) and older, less frequently used data is stored on slower (less expensive) media (e.g., tape).

hub: a device that splits one network cable into a set of separate cables, each connecting to a different computer; used in a local area network to create a small-scale network by connecting several computers together.

infrastructure: the physical equipment (computers, cases, racks, cabling, etc.) that comprises a computer system.

initiator: a SCSI device that requests another SCSI device (a target) to perform an operation; usually a host computer acts as an initiator and a peripheral device acts as a target.

I/O: input/output; reception (read) or transmission (write) of computer signals; the entire connection path between the CPU bus and the disk drives.

IOPS: I/Os per second; a measure of performance for a host-attached storage device or RAID controller.

interface: a connection between hardware devices, applications, or different sections of a computer network.

Internet: a worldwide system of linked computer networks.

Internet service provider (ISP): a company that provides Internet access services to consumers and businesses; ISPs lease connections from Internet backbone providers; while most ISPs are small companies that service a local area, there are also regional and national ISPs (such as America Online).

interoperability: the ability of one computer system to control another, even though the two systems are made by different manufacturers.

intranet: a computer network, based on Internet technology, that is designed to meet the internal needs for sharing information within a single organization or company.

JBOD: just a bunch of disks; a disk array without a controller.

kernel: the core of an operating system such as Windows 98, Windows NT, Mac OS or Unix; provides basic services for the other parts of the operating system, making it possible for it to run several programs at once (multitasking), read and write files and connect to networks and peripherals.

local area network: a network of computers within a limited area (e.g., a company or organization).

legacy: a computer, system, or software that was created for a specific purpose but is now outdated; anything left over from a previous version of the hardware or software.

LTO: linear tape open; a new standard tape format developed by HP, IBM, and Seagate; expected availability in 2000.

LUN: logical unit number; an addressing scheme used to define SCSI devices on a single SCSI bus.

megabyte: approximately one million bytes, 1,024 kilobytes

mirroring: a method of storage in which data from one disk is duplicated on another disk so that both drives contain the same information, thus providing data redundancy.

mission critical: any computer process that cannot fail during normal business hours; some computer processes (e.g., telephone systems) must run all day long and require 100 percent uptime.

MSBF: mean swaps between failure; a statistical calculation used to predict the average usefulness of a robotic device (e.g., a tape library) with any interruption of service. MTBF: mean time between failure; a statistical calculation used to predict the average usefulness of a device without any interruption of service.

MTTR: mean time to repair; the average amount of time required to resolve most hardware or software problems with a given device.

multiplatform: the ability of a product or network to support a variety of computer platforms (e.g. IBM, Sun, Macintosh); also referred to as cross-platform.

network-attached storage (NAS): a disk array storage system that is attached directly to a network rather than to the network server (i.e., host attached); functions as a server in a client/server relationship, has a processor, an operating system or micro-kernel, and processes file I/O protocols such as SMB and NFS.

network service provider (NSP): a company that provides the national or international packet-switching networks that carry Internet traffic; also called a backbone operator.

node (or network node): any device that is directly connected to the network, usually through Ethernet cable; nodes include file servers and shared peripherals.

NT (Microsoft Windows NT): an operating system developed by Microsoft for high-performance processors and networked systems.

OEM: original equipment manufacturer; a company that manufactures a given piece of hardware (unlike a value-added reseller, which changes and repackages the hardware).

open systems network: a network comprised of equipment that conforms to industry standards of interoperability between different operating systems (e.g., Unix, Windows NT).

operating system: the master control program (e.g., Windows) that manages a computer's internal functions and provides a means of control to the computer's operations and file system.

parity data: a block of information mathematically created from several blocks of user data to allow recovery of user data contained on a drive that has failed in an array; used in RAID levels 3 and 5.

PCI: personal computer interconnect; an industry-standard bus used in servers, workstations and PCs.

petabyte: 1,024 terabytes.

platform: a hardware standard, such as IBM, Sun or Macintosh, etc

proprietary: privately developed and owned technology.

protocol: a standard that specifies the format of data and rules to be followed in data communication and network environments.

rackmount: the cabinet that houses a server/storage workstation (also referred to as a server rack); to mount equipment into a cabinet.

RAID: Redundant Array of Independent (or inexpensive) Disks; a collection of storage disks with a controller (or controllers) to manage the storage of data on the disks.

real-time: immediate processing of input or notification of status.

RISC: reduced instruction set computer; a computer processing architecture that requires fewer instructions to run applications, thus increasing processing speed.

router: an electronic device that connects two or more networks and routes incoming data packets to the appropriate network.

SAN: Storage Area Network; a network infrastructure of shared multi-host storage, linking all storage devices as well as interconnecting remote sites.

scalable: the ability of a product or network to accommodate growth.

SCSI: small computer system interface; an interface that serves as an expansion bus that can be used to connect hard disk drives, tape drives, and other hardware components.

server: a computer that stores application and data files for all workstations on a network; also referred to as a file server.

spindle: mechanism inside a hard disk drive that moves the heads into place; the axle on which a disk turns.

SSA: serial storage architecture; a high-speed method of connecting disk, tape, and CD-ROM drives, printers, scanners, and other devices to a computer.

striping: a method of storage in which a unit of data is distributed and stored across several hard disks, which improves access speed but does not provide redundancy.

sustained mode: the measured transfer rate of a given device during normal operation.

switch: a network traffic monitoring device that controls the flow of traffic between multiple network nodes.

systems integrator: an individual or company that combines various components and programs into a functioning system, customized for a particular customer's needs.

target: a SCSI device that performs an operation requested by an initiator.

TCQ: tag command queuing; a feature introduced in the SCSI-2 specification that permits each initiator to issue commands accompanied by instructions for how the target should handle the command; the initiator can either request the command to be executed at the first available opportunity, in the order in which the command was received, or at a time deemed appropriate by the target.

telco: abbreviation for "telecommunications company."

terabyte: approximately one trillion bytes, 1,024 gigabytes.

throughput: measures the number of service requests on the I/O channel per unit of time.

topology: geometric arrangement of nodes and cable links in a local area network; may be either centralized and decentralized.

transfer rate: the number of megabytes of data that can be transferred from the read/write heads to the disk controller in one second.

turnkey: a product or system that can be plugged in, turned on, and operated with little or no additional configuring.

Unix: an operating system that supports multitasking and is ideally suited to multi-user applications (such as networks).

VAR: value-added reseller; a business that repackages and improves hardware manufactured by an original equipment manufacturer.

WAN: wide-area network; a network that uses high-speed, long-distance communications technology (e.g., phone lines and satellites) to connect computers over long distances.

Web cache: a Web cache fills requests from the Web server, stores the requested information locally, and sends the information to the client; the next time the web cache gets a request for the same information, it simply returns the locally cached data instead of searching over the Internet, thus reducing Internet traffic and response time.

Web site: a location on the World Wide Web that is owned and managed by an individual, company or organization; usually contains a home page and additional pages that include information provided by the site's owner, and may include links to other relevant sites.

World Wide Web: a global hypertext system operating on the Internet that enables electronic communication of text, graphics, audio, and video.

XOR engine: process or set of instructions that calculates data bit relationships in a RAID subsystem.

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