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 While many of the definitions are unchanged, some of the definitions may be out of date and some of the terms may no longer be in use in the Data Center industry.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

Frame for housing electronic equipment that is enclosed by doors and is standalone. This is generally found with high-end servers

Cabinet Air

See air, cabinet


Conductive anodic failure


Category 3 balanced cable


Category 5 balanced cable


Constant air volume

Central Office (CO)

A building within a telephone network that houses equipment for processing (receiving, transmitting, redirecting, etc.) voice signals and digital data, connecting a larger number of lower speed to a smaller number of higher speed lines

Central Processing Unit (CPU)

Also called a processor. In a computer, the CPU is the processor on an IC chip that serves as the heart of the computer, containing a control unit, the arithmetic and logic unit (ALU), and some form of memory. It interprets and carries out instructions, performs numeric computations, and controls the external memory and peripherals connected to it


The physical framework of the computer system that houses all electronic components, their interconnections, internal cooling hardware, and power supplies

Chilled Water System

A type of air conditioning system that has no refrigerant in the unit itself. The refrigerant is contained in a chiller, which is located remotely. The chiller cools water, which is piped to the air conditioner to cool the space. An air or process conditioning system containing chiller(s), water pump(s), a water piping distribution system, chilled-water cooling coil(s), and associated controls. The refrigerant cycle is contained in a remotely located water chiller. The chiller cools the water, which is pumped through the piping system to the cooling coils.


Identifies the actual microprocessor, the physical package, containing one or more cores

Classes of Fires

* Class A: Fires involving ordinary combustibles such as paper, wood, or cloth
* Class B: Fires involving burning liquids
* Class C: Fires involving any fuel and occurring in or on energized electrical equipment
* Class D: Fires involving combustible metals (such as magnesium)


A server system that can operate independently, but has some interdependence with another server system


Two or more interconnected servers that can access a common storage pool. Clustering prevents the failure of a single file server from denying access to data and adds computing power to the network for large numbers of users

CMOS Electronic Technology

This technology draws considerably less power than bipolar semiconductor technology in standby mode, and so it replaced many of the digital bipolar applications around the early 1990s

Coefficient of Performance (COP) - Cooling

The ratio of the rate of heat removal to the rate of energy input in consistent units for a complete cooling system or factory-assembled equipment as tested under a nationally recognized standard or designated operating conditions

Cold Aisle

See hot aisle/cold aisle

Cold Plate

Cold plates are typically aluminum or copper plates of metal that are mounted to electronic components. Cold plates can have various liquids circulating within their channels. Typically, a plate with cooling passages through which liquid flows to remove the heat from the electronic component to which it is attached


The process of ensuring that systems are designed, installed, functionally tested, and capable of being operated and maintained to perform in conformity with the design intent. It begins with planning and includes design, construction, start-up, acceptance, and training, and can be applied throughout the life of the building

Commissioning Levels

* Factory acceptance tests (Level 1 commissioning): Testing of products prior to leaving their place of manufacture
* Field component verification (Level 2 commissioning): Inspection and verification of products upon receipt
* System construction verification (Level 3 commissioning): Field inspections and certifications that components are assembled and properly integrated into systems as required by plans and specifications
* Site acceptance testing (Level 4 commissioning): Activities that demonstrate that related components, equipment, and ancillaries that make up a defined system operate and function to rated, specified, and/or advertised performance criteria
* Integrated systems tests (Level 5 commissioning): Testing of redundant and backup components, systems, and groups of interrelated systems to demonstrate that they respond as predicted to expected and unexpected anomalies

Commissioning Plan

A document that defines the verification and testing process to ensure the project delivers what is expected, including training, documentation, and project close-out

Communication Equipment

Equipment used for information transfer. The information can be in the form of digital data for data communications or analog signals for traditional wireline voice communication
* Core network or equipment: A core network is a central network into which other networks feed. Traditionally, the core network has been the circuit-oriented telephone system. More recently, alternative optical networks bypass the traditional core and implement packet-oriented technologies. Significant to core networks is "the edge," where networks and users exist. The edge may perform intelligent functions that are not performed inside the core network
* Edge equipment or devices: In general, edge devices provide access to faster, more efficient backbone and core networks. The trend is to make the edge smart and the core "dumb and fast." Edge devices may translate between one type of network protocol and another


A program that translates (presumably) human-readable source code into a form that is native for a particular machine

Computational Fluid Dynamics (CFD)

A computational technology that enables you to study the dynamics of fluid flow and heat transfer numerically

Compute Server

Servers dedicated for computation or processing that are typically required to have greater processing power (and, hence, dissipate more heat) than servers dedicated solely for storage (also see server)


Term that applies to any computer application that demands a lot of computation, such as meteorology programs and other scientific applications. A similar but distinct term, computer-intensive, refers to applications that require a lot of computers, such as grid computing. The two types of applications are not necessarily mutually exclusive. Some applications are both compute- and computer-intensive

Computer Room Air Conditioning (CRAC)

A modular packaged environmental control unit designed specifically to maintain the ambient air temperature and/or humidity of spaces that typically contain data communcations equipment. These products can typically perform all (or a subset) of the following functions: cool, reheat, humidify, dehumidify. They may have multiple steps for some of these functions. CRAC units should be specifically designed for data and communications equipment room applications and meet the requirements of ANSI/ASHRAE Standard 127-2001, Method of Testing for Rating Computer and Data Processing Room Unitary Air Conditioners

Computer System Availability

Probability that a computer system will be operable at a future time (takes into account the effects of failure and repair/maintenance of the system)

Computer System Reliability

Probability that a computer system will be operable throughout its mission duration (only takes into account the effects of failure of the system)


Heat exchanger in which vapor is liquefied (state change) by the rejection of heat as a part of the refrigeration cycle

Conditioned Air

See air, conditioned


Removal of heat

Cooling Tower

Heat-transfer device, often tower-like, in which atmospheric air cools warm water, generally by direct contact (heat transfer and evaporation)

Cooling, Air

Conditioned air is supplied to the inlets of the rack/cabinet/server for convective cooling of the heat rejected by the components of the electronic equipment within the rack. It is understood that within the rack, the transport of heat from the actual source component (e.g., CPU) within the rack itself can be either liquid- or air-based, but the heat rejection media from the rack to the building cooling device outside the rack is air. The use of heat pipes or pumped loops inside a server or rack where the liquid remains is still considered air cooling

Cooling, Liquid

Conditioned liquid is supplied to the inlets of the rack/cabinet/server for thermal cooling of the heat rejected by the components of the electronic equipment within the rack. It is understood that within the rack, the transport of heat from the actual source component (e.g., CPU) within the rack itself can be either liquid- or air-based (or any other heat transfer mechanism), but the heat rejection media to the building cooling device outside of the rack is liquid


Used to identify the core set of architectural, computational processing elements that provide the functionality of a CPU

Core Network or Equipment

See communication equipment


SPEC uses often to mean applications that are primarily bound by the available processing power. Typically, these spend most of their time performing calculations, comparisons, or transformations and do little or no I/O and spend very little time in the operating system


CPU2000 is the current version of the CPU component benchmark suite from SPEC. It replaces CPU95


CPU2006 is the name given to the ongoing effort to replace the current CPU2000 product


CPU92 is a now outdated CPU component benchmark suite from SPEC. This was replaced by CPU95


CPU95 is an earlier version of the CPU component benchmark suite from SPEC, which replaced CPU92 and the even older CPU89. This suite has in turn been replaced by CPU2000


Cyclic redundancy check

Cross Connect

A group of connection points, often wall- or rack-mounted in a wiring closet, used to mechanically terminate and interconnect twisted-pair building wiring

Cubic Feet per Minute (CFM)

Commonly used to measure the rate of air flow in systems that move air