Abbreviation for the data and communications industry
TGG 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 While many of the definitions are unchanged, some of the definitions may be out of date and some of the terms may no longer be in use in the Data Center industry.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.
Datacom
Dataset
The set of inputs for a particular benchmark. There may be more than one dataset available for each benchmark each serving a different purpose (e.g., measurement versus testing) or configured for different problem sizes (small, medium, large, etc.
Daughter Card
Also called daughter board. A printed circuit board that plugs into another circuit board to provide extended feature(s). A daughter card accesses its parent card's circuitry directly through the interconnection between the boards. A mezzanine card is a kind of daughter card that is installed such that it lies in the same plane, but on a second level above its parent
dBm
Decibels referenced to 1.0 mW
DC
Direct Current a form of power distribution. Source: ASHRAE
DC
Data Center. Source: OCP
DCIM
Data Center Infrastructure Management. Source: ASHRAE
DDR
Double data rate. A type of memory; a number behind DDR indicates the generation. Source: ASHRAE
Dead-end Service Rating (Valves)
Valves rated for dead-end service can be placed at the end of a pipe without a cap (i.e., with one end at atmospheric pressure) and will not have any leakage of fluid across the valve at the service pressure rating of the valve
Dehumidification
The process of removing moisture from air
Dew point
The temperature at which water vapor has reached the saturation point (100% relative humidity)
Dew-point Temperature
See temperature, dew-point
Dichotomous Sampler
Piece of measurement equipment that collects airborne particulates and separates them by size for analysis
Dielectric Fluid
A fluid that is a poor conductor of electricity
DIMM
Dual in-line memory module. Source: ASHRAE
Direct Current (DC)
An electric current flowing in one direction only. Source: Oxford Languages
Direct Expansion (DX) System
A system in which the cooling effect is obtained directly from the refrigerant. It typically incorporates a compressor, and in most cases, the refrigerant undergoes a change of state in the system
Direct Liquid Cooling (DLC)
A type of liquid cooling used to cool CPUs and GPUs. Cooling a CPU involves running a cold liquid (contained) over the top of a running chip. A thermal transfer material is used to conduct the heat from the top of the chip to a cold plate with the liquid flowing over the plate. The cooler liquid picks up the heat from the chip and is carried away to be cooled elsewhere. The cooler liquid is then returned to the chip in a closed loop system. Source: Supermicro
Direct to Chip (DTC) or (D2C)
A type of liquid cooling used to cool CPUs and GPUs. Cooling a CPU involves running a cold liquid (contained) over the top of a running chip. A thermal transfer material is used to conduct the heat from the top of the chip to a cold plate with the liquid flowing over the plate. The cooler liquid picks up the heat from the chip and is carried away to be cooled elsewhere. The cooler liquid is then returned to the chip in a closed loop system. Source: Supermicro
Direct water-cooled
Power that is transferred directly to an attached heat transfer component such as a cold plate. Source: ASHRAE
Discounting
A mathematical operation that aims to make monetary (or other) amounts received or expended at different times (years) comparable across time. The discounter uses a fixed or possibly time varying discount rate from year to year that makes future value worth less today (if the discount rate is positive). The choice of discount rate(s) is debated as it is a judgement based on hidden and/or explicit values. Source: IPCC
Disk Unit
Hard disk drive installed in a piece of data communications equipment, such as a personal computer, laptop, server, or storage product
Disruptive innovation
Demand-led technological change that leads to significant system change and is characterized by strong exponential growth. Source: IPCC
Diversity (from ASHRAE, industry)
Two definitions for diversity exist, diverse routing and diversity from maximum:
* Systems that employ an alternate path for distribution are said to have diverse routing. In terms of an HVAC system, it might be used in reference to an alternate chilled water piping system. To be truly diverse (and of maximum benefit), both the normal and alternate paths must each be able to support the entire normal load.
* Diversity can also be defined as a ratio of maximum to actual for metrics such as power loads. For example, the nominal power loading for a rack may be based on the maximum configuration of components all operating at their maximum intensities. Diversity would take into account variations from the maximum in terms of rack occupancy, equipment configuration, operational intensity, etc., to provide a number that could be deemed to be more realistic
Diversity (from ASHRAE)
A factor used to determine the load on a power or cooling system based on the actual operating output of the individual equipment rather than the full-load capacity of the equipment
DMTF Redfish
Standard designed to deliver simple and secure management for converged, hybrid IT and the Software Defined Data Center (SDDC). Both human readable and machine capable, Redfish leverages common Internet and web services standards to expose information directly to the modern tool chain. Source: DMTF
DoE
U.S. Department of Energy. The federal agency that oversees power administration, the regulation of nuclear power reactors, and other aspects of the energy industry. Source: United States Department of Energy
Domain
A group of computers and devices on a network that are administered as a unit with common rules and procedures. Within the internet, domains are defined by the IP address. All devices sharing a common part of the IP address are said to be in the same domain
Double Data Rate Memory (DDR Memory)
An advanced version of synchronous DRAM (SDRAM) memory now used in most servers. DDR-SDRAM, sometimes called SDRAM II, can transfer data twice as fast as regular SDRAM because it can send and receive signals twice per clock cycle
Double Precision
A level of floating point accuracy that usually requires twice the space for each value than does single precision, but provides considerably more precision. For most systems running the SPEC CPU tests from the OSG (e.g. CPU2000), double precision implies a 64-bit value
Downflow
Refers to a type of air conditioning system that discharges air downward directly beneath a raised floor commonly found in computer rooms and modern office spaces
Downtime
A period of time during which a system is not operational due to a malfunction or maintenance
DPC
DIMMs per channel. Source: ASHRAE
Drives
A component type of data center class servers. Source: Intel
Dry-bulb Temperature (DB)
See temperature, dry-bulb
Drywell
A well in a piping system that allows a thermometer or other device to be inserted without direct contact with the liquid medium being measured
Dual In-line Memory Module (DIMM)
A small circuit board that usually holds memory chips. A single in-line memory module (SIMM) has card edge connections that are connected to the same signals on both sides of the PCB, whereas a DIMM has different signals on each side of the PCB
Dust
Solid particles of a substance or mixture suspended in in a gas (usually air). Source: United Nations GHS
DUT
Device Under Test. Source: OCP
Dynamic Random Access Memory (DRAM)
The most commonly used type of memory in computers. A bank of DRAM memory usually forms the computer's main memory. It is called dynamic because it needs to be refreshed periodically to retain the data stored within
EC Number or (ECN)
A reference number used by the European Communities to identify dangerous substances, in particular those registered under EINECS. Source: United Nations GHS
EC-class
Equipment cooling class
ECM
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 Data Center
Edge data center. Source: PwC
Edge Equipment
See communication equipment
EER
Energy efficiency ratio
Efficiency
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
EINECS
European Inventory of Existing Commercial Chemical Substances. Source: United Nations GHS
ELC
Electrical Loss Component per ANSI / ASHRAE Standard 90.4 – 2016. The design ELC is the combined losses of three segments of the electrical chain: incoming electrical service segment, UPS segment, and ITE distribution segment. Source: ASHRAE
Electrical Bus
See bus, power
Electrolyte
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 (EC)
EC motor is widely used for fans and pumps to reduce the drive energy consumption. Source: Schneider Electric
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
EMI
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
The ability to do work or the ability to move an object. Electrical energy is usually measured in kilowatt-hours (kWh), while heat energy is usually measured in British thermal units (Btu).power derived from the utilization of physical or chemical resources, especially to provide light and heat or to work machines. Source: Oxford Languages
Energy Efficiency
Energy efficiency can be defined for a component or service as the amount of energy required in the production of that component or service; for example, the amount of steel that can be produced with one billion Btu of energy. Energy efficiency is improved when a given level of service is provided with reduced amounts of energy inputs, or services or products are increased for a given amount of energy input. Source: United States Office of Energy Efficiency and Renewable Energy (EERE)
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)
Enterprise Data Center
Data center which your organization owns/operates, hosting only your organization’s workloads. Source: Uptime Institute
Enthalpy (Total Heat)
See heat, total
EPDM
Ethylene Propylene Diene Monomer: a type of synthetic rubber. Source: OCP
Equipment
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
ESD
Electro-static discharge. Source: ASHRAE
ESG
Environmental, social, and governance criteria are a set of standards for a company’s behavior used by socially conscious investors to screen potential investments. Environmental criteria consider how a company safeguards the environment, including corporate policies addressing climate change, for example. Social criteria examine how it manages relationships with employees, suppliers, customers, and the communities where it operates. Governance deals with a company’s leadership, executive pay, audits, internal controls, and shareholder rights. Source: ASHRAE or an alternate definition of A set of standards that guides companies to operate responsibly, deliver sustainable outcomes and provide meaningful benefits to a broad range of stakeholders. Source: PwC
Ethernet
A networking system that enables high-speed data communication over coaxial cables
ETSI
European Telecommunications Standards Institute
EU
European Union. Source: United Nations GHS
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
Executable
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
F-GHGs
Fluorinated Greenhouse gases. Source: GEC
Facility Manager
A stakeholder in the decision to invest, divest, use, source liquid cooled data center environments. Source: United States Department of Energy CoE
Fan
Device for moving air by two or more blades or vanes attached to a rotating shaft.
* Airfoil fan: Shaped blade in a fan assembly to optimize flow with less turbulence
* Axial fan: Fan that moves air in the general direction of the axis about which it rotates
* Centrifugal fan: Fan in which the air enters the impeller axially and leaves it substantially in a radial direction
* Propeller fan: Fan in which the air enters and leaves the impeller in a direction substantially parallel to its axis
Fan Sink
A heat sink with a fan directly and permanently attached
Fans
A component type of data center class server. Source: Intel
Fault Tolerance
The ability of a system to respond gracefully and meet the system performance specifications to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure. Many fault-tolerant computer systems mirror all operations. That is, every operation is performed on two or more duplicate systems, so if one fails, the other can take over
FCS
Frame check sequence
FEC
Forward error correction
Fenestration
An architectural term that refers to the arrangement, proportion, and design of window, skylight, and door systems within a building
Fiber Optic Cable
A cable containing one or more optical fibers as specified in IEEE 802.3, 15.3.1
Fiber Optic Cable Assembly
A LENGTH OF FIBER OPTIC CABLE THAT HAS BEEN TERMINATED WITH A CONNECTOR, PIGTAIL OR OTHER COMPONENT. [ KEY=143463;UNSPSC=26121650;V23.07 || ECCMA || ISO 22745-11 COMPLIANCE Source: eOTD ECCMA Open Technical Dictionary is an ISO 22745 compliant dictionary managed by ECCMA
Fileset
A pre-defined set of files that are used within a benchmark workload. Usually a fileset has specific characteristics that are relevant to how the benchmark performs its work
Filter Dryer
Encased desiccant, generally inserted in the liquid line of a refrigeration system and sometimes in the suction line, to remove entrained moisture, acids, and other contaminants
Firmware
Software that has been encoded onto read-only memory (ROM). Firmware is a combination of software and hardware. The code or data programmed into ROMs, PROMs, EPROMs, and flash memory is firmware
Flammability
Flammability is the capability of a material or substance to burn, ignite, combust, or catch fire. It refers to the rate and likelihood of such phenomena occurring a parameter of evaluation for fluids used to cool data center equipment. Source: Corrosionpedia.com