Legacy Glossary

This is a glossary of older terms. While many of the definitions are unchanged, some of the definitions may be out of date and some of the terms may no longer be in use in the Data Center industry. This legacy glossary provides definitions for hundreds of information and communications technology (ICT) and data center terms and acronyms. Arranged alphabetically and searchable, the glossary explains common industry vocabulary.
1 A B C D E F G H I K L M N O P R S T U V W Z

Equipment cooling class


Electronically commutated motor

Economizer, Air

A ducting arrangement and automatic control system that allow a cooling supply fan system to supply outdoor (outside) air to reduce or eliminate the need for mechanical refrigeration during mild or cold weather

Economizer, Water

A system by which the supply air of a cooling system is cooled directly or indirectly or both by evaporation of water or by other appropriate fluid (in order to reduce or eliminate the need for mechanical refrigeration)

Edge Equipment

See communication equipment


Energy efficiency ratio


The ratio of the output to the input of any system. Typically used in relation to energy. Smaller amounts of wasted energy denote high efficiencies

Efficiency, HVAC System

The ratio of the useful energy output (at the point of use) to the energy input in consistent units for a designated time period expressed in percent

Electrical Bus

See bus, power


A substance that dissociates free ions when dissolved (or molten) to produce an electrically conductive medium

Electrolyte, Absorbed

Valve regulated lead-acid (VRLA) cells of this design are constructed with a controlled volume of liquid electrolyte contained in a highly absorbent, blotter-like separator positioned between closely spaced plates. This non-woven separator distributes the electrolyte uniformly and maintains it in contact with the plate active material, while permitting the passage of oxygen evolved during charging. Cells with absorbed electrolyte technology have inherently low internal resistance and can be designed to provide a very high-rate, short-duration current. Cells with absorbed electrolyte are also known as absorbed glass mat (AGM) types

Electrolyte, Gelled

Valve regulated lead-acid (VRLA) cells of this design are similar to vented designs, except that the electrolyte has been "gelled" to immobilize it. They can provide a high-rate, short-duration current, but because of the higher internal resistance, they are not as effective as the absorbed electrolyte design. However, the higher thermal conductivity in gelled designs makes them better suited for elevated temperature applications than equivalent absorbed electrolyte cells. A gelled electrolyte cell is typically heavier and larger than an absorbed electrolyte cell for a given capacity

Electromagnetic Compatibility (EMC)

The ability of electronic equipment or systems to operate in their intended operational environments without causing or suffering unacceptable degradation because of electromagnetic radiation or response

Electronically Commutated Motor (ECM)

An EC motor is a DC motor with a shunt characteristic. The rotary motion of the motor is achieved by supplying the power via a switching device, the so-called commutator. On the EC motors, this commutation is performed using brushless electronic semiconductor modules

Electronics, Air- and Liquid-cooled

Electronic equipment that uses both air and liquid

Electronics, Air-cooled

Electronic equipment that is directly cooled by air

Electronics, Liquid-cooled

Electronic equipment that is directly cooled by liquid

Electrostatic Discharge (ESD)

The sudden flow of electricity between two objects at different voltage potentials. ESD is a primary cause of integrated circuit damage or failure


Electromagnetic interference

End Station

A system attached to a LAN that is an initial source or a final destination of MAC frames transmitted across that LAN. A network layer router is, fro the perspective of the LAN, an end station. A MAC bridge, in its role of forwarding MAC frames from one LAN to another, is not an end station (see IEEE 802.3, Clause 43)

Energy Efficiency Ratio (EER)

The ratio of net equipment cooling capacity in BTU/h to total rate of electric input in watts under designated operating conditions. When consistent units are used, this ratio becomes equal to COP (see also coefficient of performance)

Enthalpy (Total Heat)

See heat, total


Refers to, but not limited to, servers, storage products, workstations, personal computers, and transportable computers. May also be referred to as electronic equipment or IT equipment

Equipment Air

See air, equipment

Equipment Recommended Operation Range

Manufacturer's specifications generally reference a range in which a piece of equipment CAN function. A recommended range refers to the range at which equipment is the most efficient and realizes the least amount of wear and tear, extending its useful life

Equipment Room

Data center or telecommunications central office room that houses computer and/or telecommunications equipment. For rooms housing mostly telcommuncations equipment, see telcordia GR-3028-CORE

Equipment, Air cooled

Equipment conditioned by removal of heat using air

Equipment, Liquid cooled

Equipment coniditioned by the removal of heat using a liquid


A networking system that enables high-speed data communication over coaxial cables


European Telecommunications Standards Institute

Evaporative Condenser

Condenser in which the removal of heat from the refrigerant is achieved by the evaporation of water from the exterior of the condensing surface induced by the forced circulation of air and sensible cooling by the air

Exchanger, Rotary Heat

A heat exchanger in which the heat exchange surface rotates


As an adjective, executable means that the described item can be executed. In computer talk, executable has been also used as a noun, where it means an executable program, or in other words, something that is ready to run without further modification. Commonly, the term executable is used to refer to the binary file that is the final result of compiling source code