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 While many of the definitions are unchanged, some of the definitions may be out of date and some of the terms may no longer be in use in the Data Center industry.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

IEEE 802.3 physical coding sublayer for serial 10 GB/s operation (see IEEE 802.3, Clause 49)


IEEE 802.3 physical layer specification for a 1000 MB/s CSMA/CD LAN using four pairs of Category 5 balanced copper cabling (see IEEE 802.3, Clause 40)


IEEE 802.3 physical layer specification for 10 GB/s using 10GBASE-X encoding over four lanes over shielded balanced copper cabling (see IEEE 802.3, Clause 54)


IEEE 802.3 physical coding sublayer for 10 GB/s operation over XAUI and four lane PMDs (see IEEE 802.3, Clause 48)

Absorbed Electrolyte

See electrolyte, absorbed


American Conference of Governmental Industrial Hygienists


Air changes per hour. Typically referring to outdoor air changes per hour


Generally, a measure of the noise level in an environment or from a sound source. For a point in an environment, the quantity is sound pressure level in decibels (dB). For a sound source, the quantity is sound power level in either decibels (dB) or bels (B). Either of these quantities may be stated in terms of individual frequency bands or as an overall A-weighted value. Sound output typically is quantified by sound pressure (dBA) or sound power (dB). Densely populated data and communications equipment centers may cause annoyance, affect performance, interfere with communications, or even run the risk of exceeding OSHA noise limits (and thus potentially cause hearing damage), and reference should be made to the appropriate OSHA regulations and guidelines (OSHA 1996). European occupational noise limits are more stringent than OSHA's and are mandated in EC Directive 2003/ 10/EC (European Council 2003)

Aggregation Link

An instance of a MAC-physical layer-medium physical layer-MAC entity between a pair of aggregation systems (see IEEE 802.3, Clause 43)

Aggregation Port

An instance of a MAC-physical layer entity within an aggregation system (see IEEE 802.3, Clause 43)

Aggregation System

A uniquely identifiable entity comprising, among other things, an arbitrary grouping of one or more ports for the purpose of aggregation. An instance of an aggregated link always occurs between exactly two aggregation systems. A physical device may comprise a single aggregation system or more than one aggregation system (see IEEE 802.3, Clause 43)

Agile Device

A device that supports automatic switching between multiple physical layer technologies (see IEEE 802.3, Clause 28)


Air-handling unit, which is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system

Air Cooling

See cooling, air

Air Economizer

See economizer, air

Air Inlet Temperature

The temperature measured at the inlet at which air is drawn into a piece of equipment for the purpose of conditioning its components

Air Outlet Temperature

The temperature measured at the outlet at which air is discharged from a piece of equipment

Air Short-cycling

Air conditioners are most efficient when the warmest possible air is returned to them. When cooler-than-expected air is returned to the air conditioner, it will perhaps mistakenly read that as the space temperature being satisfied. This air short-cycling is because the air is not picking the heat from the space before returning to the air conditioner (see also Air, Bypass)

Air Space

Where the air space below a raised floor or above a suspended ceiling is used to recirculate information technology equipment room/information technology equipment area environmental air, the wiring shall conform to Article 645 of NFPA 70, National Electrical Code

Air, Bypass

Air diverted around a cooling coil in a controlled manner for the purpose of avoiding saturated discharge air. On an equipment room scale, bypass air can also refer to the supply air that short-cycles around the load and returns to the air handler without producing effective cooling at the load

Air, Cabinet

Air (typically for the purposes of cooling) that passes through a cabinet housing data communications equipment

Air, Conditioned

Air treated to control its temperature, relative humidity, purity, pressure, and movement

Air, Equipment

Airflow that passes through the IT or data communications equipment

Air, Return (RA)

Air extracted from a space and totally or partially returned to an air conditioner, furnace, or other heat source

Air, Supply

Air entering a space from an air-conditioning, heating, or ventilating apparatus

Air- and Liquid-cooled Electronics

See electronics, air- and liquid-cooled

Air- and Liquid-cooled Rack

See rack, air- and liquid-cooled

Air- and Liquid-cooled Server

See server, air- and liquid-cooled

Air-cooled Data Center (ASHRAE glossary)

See data center, air- and liquid-cooled

Air-cooled Electronics

See electronics, air-cooled

Air-cooled Rack

See rack, air-cooled

Air-cooled System

See system, air-cooled

Aisle, Cold

See hot aisle/cold aisle

Aisle, Hot

See hot aisle/cold aisle


The portion of a fire alarm control panel or a remote device attached to the fire alarm control panel that displays the information associated with a notification. Notifications may include alarm or trouble conditions


A discrepancy between the actual and desired characteristics of an item. This definition is derived from ANSI T1.416-1999 and ANSI T1.105-1995, which take precedence


American National Standards Institute


A collection of data items usually laid out linearly in memory for simple access with an integer index from the base of the array. Many scientific applications use arrays to contain the dataset that they are analyzing. The larger the dataset, the larger the array size needs to be to fit the data

Associate Member

A membership class available to non-profit organizations at a significantly reduced cost. Allows for access to the benchmarks under development on the condition of significant involvement in the development process. Each group has their own rules and requirements regarding associate membership. Contact SPEC for details

ASTM International

Formerly the American Society for Testing and Materials (ASTM)


Attachment unit interface


The algorithm that allows two devices at either end of a link segment to negotiate common data service functions (see IEEE 802.3, Clause 28)


A percentage value representing the degree to which a system or component is operational and accessible when required for use

Availability Date

The date upon which that part of the system becomes generally available, that is available to anyone willing to pay the appropriate price and take immediate delivery


A printed circuit board with connectors where other cards are plugged. A backplane does not usually have many active components on it in contrast to a system board

Balanced Cable

A cable consisting of one or more metallic symmetrical cable elements (twisted pairs or quads) (from ISO/IEC 11801)


Data traffic through a device usually measured in bits per second


For SPEC's purposes, baseline refers to a configuration that is more general and hopefully simpler than one tuned for a specific benchmark. Usually a baseline configuration needs to be effective across a variety of workloads, and there may be further restrictions, such as requirements about the ease-of-use for any features utilized. Commonly baseline is the alternative to a peak configuration.


A document that captures the relevant physical aspects of the facility to achieve the performance requirements in support of the mission (as stated in the owner's program document)

Battery, VLA

Vented lead-acid battery

Battery, VRLA

Valve regulated lead-acid battery

Baud (Bd)

A unit of signaling speed expressed as the number of times per second the signal can change the electrical state of the transmission line or other medium. Depending on the encoding strategies, a signal event may represent a single bit, more, or less than one bit. Contrast with bit rate, bits per second (from IEEE 610.7-1995 [B38])


* A frame containing electronic equipment
* A space in a rack into which a piece of electronic equipment of a certain size can be physically mounted and connected to power and other input/output devices


A reference point. Originally, a mark on a workbench used to compare the lengths of pieces so as to determine whether one was longer or shorter than desired. For computers, a benchmark is a test, or set of tests, designed to compare the performance of one computer system against the performance of others. A benchmark is not necessarily a capacity planning tool. That is, benchmarks may not be useful in attempting to guess the correct size of a system required for a particular use. In order to be effective in capacity planning, it is necessary for the test to be easily configurable to match the targeted use. In order to be effective as a benchmark, it is necessary for the test to be rigidly specified so that all systems tested perform comparable work. These two goals are often at direct odds with one another with the result that benchmarks are usually useful for comparing systems against each other, but some other test is often required to establish what kind of system is appropriate for an individual's needs

Benchmark Sponsor

Every benchmark code of SPEChpc96 has a technical advisor who is knowledgeable about the code and the scientific/engineering problem, possibly with the help of experts outside the SPEC organization


Bit error ratio tester


To be specific, binary refers to a numeric representation that is comprised of (frequently very long) sequences of only two values, usually 0 and 1. Deep down at their very core, most computers really only understand 0 and 1 (or in other words, some little bit of information is either "off" or "on"). Thus, the term binary is frequently used to describe anything already translated to the form that is closest to what the system understands natively


Basic input/output system. The BIOS gives the computer a built-in set of software instructions to run additional system software during computer boot-up

Bipolar Semiconductor Technology

This technology was popular for digital applications until the CMOS semiconductor technology was developed. CMOS drew considerably less power in standby mode, and so it replaced many of the bipolar applications around the early 1990s

Bit Error Ratio (BER)

The ratio of the number of bits received in error to the total number of bits received

Bit Rate (BR)

The total number of bits per second transferred to or from the media access control (MAC). For example, 100BASE-T has a bit rate of one hundred million bits per second (108 b/s)

Blade Server

A modular electronic circuit board, containing one, two, or more microprocessors and memory, that is intended for a single, dedicated application (such as serving web pages) and that can be easily inserted into a space-saving rack with many similar servers. One product offering, for example, makes it possible to install up to 280 blade server modules vertically in a single floor-standing cabinet. Blade servers, which share a common high-speed bus, are designed to create less heat and thus save energy costs as well as space

Blanking Panels

Panels typically placed in unallocated portions of enclosed IT equipment racks to prevent internal recirculation of air from the rear to the front of the rack


An air-moving device (also see fan)


Building management system


A layer 2 interconnection device that does not form part of a CSMA/CD collision domain, but conforms to the ISO/IEC 15802-3: 1998 [ANSI/IEEE 802.1D, 1998 Edition]. A bridge does not form part of a CSMA/CD collision domain, but rather appears as a media access control (MAC) to the collision domain (see also IEEE 100)


Bit time


British thermal units. The amount of heat required to raise one pound of water one degree Fahrenheit, a common measure of the quantity of heat

Building Automation System (BAS)

Centralized building control typically for the purpose of monitoring and controlling environment, lighting, power, security, fire/life safety, and elevators

Bus, Electrical

See bus, power

Bus, Power (or Electrical Bus)

A physical electrical interface where many devices share the same electric connection, which allows signals to be transferred between devices, allowing information or power to be shared

Bypass Air

See air, bypass


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

Data Center

A building or portion of a building whose primary function is to house a computer room and its support areas. Data centers typically contain high-end servers and storage products with mission-critical functions

Data Center Availability

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

Data Center Energy Practitioner (DCEP)

The data center industry and DOE partnered to develop the Data Center Energy Practitioner (DCEP) Program. The DCEP training program certifies energy practitioners qualified to evaluate the energy status and efficiency opportunities in data centers. More information at https://datacenters.lbl.gov/dcep

Data Center Reliability

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

Data Center, Air-cooled

Facility cooled by forced air transmitted by raised floor, overhead ducting, or some other method; A data center with only air-cooled equipment

Data Center, Liquid- and Air-cooled

Data center with both chilled air and liquid available

Data Center, Liquid-cooled

Data center with only liquid-cooled equipment

Data Frame

Consists of the destination address, source address, length field, logical link control (LLC) data, PAD, and frame check sequence

Data Terminal Equipment (DTE)

Any source or destination of data connected to the local area network


Abbreviation for the data and communications industry


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


Decibels referenced to 1.0 mW

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


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

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

Disk Unit

Hard disk drive installed in a piece of data communications equipment, such as a personal computer, laptop, server, or storage product

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

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


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


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


A period of time during which a system is not operational due to a malfunction or maintenance

Dry-bulb Temperature (DB)

See temperature, dry-bulb


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

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


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


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

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


Frame check sequence


Forward error correction


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


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


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

Float Voltage

Optimum voltage level at which a battery string gives maximum life and full capacity

Floating Point

A class of arithmetic, typically used in scientific applications. Actually much like the values displayed by a calculator, the values can range from very large down to minute fractions but only the first several digits are available. Floating point is commonly used when the values being calculated can be very large - into the billions - or else involve fractions, e.g., the number of miles from earth to the next galaxy (billions and billions) or the precise temperature of a feverish baby (101.8). Floating point is the alternative to integer. For the purposes of classification for the CPU benchmarks, SPEC classifies an application to be a floating point application if that application typically spends 10% or more of its time in calculating floating point value


A family of perfluorinated liquids from 3M offering unique properties ideally suited to the demanding requirements of electronics manufacturing, heat transfer, and other specialized applications


Amount of some quantity flowing across a given area (often a unit area perpendicular to the flow) per unit time. The quantity may be, for example, mass or volume of a fluid, electromagnetic energy, or number of particles


In information technology, a footprint is the amount of space a particular unit of hardware or software occupies. Marketing brochures frequently state that a new hardware control unit or desktop display has a "smaller footprint," meaning that it occupies less space in the closet or on a desk. More recently, the term is used to describe microcomponents that take less space inside a computer

Full Disclosure Report

The complete documentation of a benchmark's results along with the relevant system and benchmark configuration information. There should be sufficient detail and coverage for someone else to be able to reproduce the tests. Each result available on this server has such a disclosure available


A small cock fitted to a pressure or other measurement gage to allow for isolation of the gage for purposes of maintenance


A hardware or software setup that translates between two dissimilar protocols, or commonly, any mechanism for providing access to another system

Gelled Electrolyte

See electrolyte, gelled

Geometric Mean

A mean (average value) that is obtained through the use of multiplication and Nth roots rather than by addition and division. To calculate, take the Nth root (the power of 1/N) of the product of all N terms. The geometric mean has the interesting property that a certain percentage change in any one of the terms has the same effect as the same percentage change in any of the other terms and even successive changes in the same term will have the same effect as if the changes were instead spread over other terms. What this means in benchmarking terms is that a 10% improvement in one benchmark has the same effect on the overall mean as a 10% improvement on any of the other benchmarks and that another 10% improvement on that benchmark will have the same effect as the last 10% improvement. Thus no one benchmark in a suite becomes more important than any of the others in the suite

Global Positioning System (GPS)

A system of satellites and receiving devices used to compute positions on earth

Heat Exchanger

Device to transfer heat between two physically separated fluids
* Counterflow heat exchanger: Heat exchanger in which fluids flow in opposite directions approximately parallel to each other
* Cross-flow heat exchanger: Heat exchanger in which fluids flow perpendicular to each other
* Heat pipe heat exchanger: See heat pipe
* Parallel-flow heat exchanger: Heat exchanger in which fluids flow approximately parallel to each other and in the same direction
* Plate heat exchanger or plate liquid cooler: Thin plates formed so that liquid to be cooled flows through passages between the plates and the cooling fluid flows through alternate passages

Heat Exchanger, Rotary

See exchanger, rotary heat

Heat Load per Product Footprint

Calculated by using product measured power divided by the actual area covered by the base of the cabinet or equipment

Heat Load, Latent

Cooling load to remove latent heat, where latent heat is a change of enthalpy during a change of state

Heat Load, Sensible

The heat load that causes a change in temperature

Heat Pipe

Also defined as a type of heat exchanger. Tubular closed chamber containing a fluid in which heating one end of the pipe causes the liquid to vaporize and transfer to the other end where it condenses and dissipates its heat. The liquid that forms flows back toward the hot end by gravity or by means of a capillary wick

Heat Sink

Component designed to transfer heat from an electronic device to a fluid. Processors, chipsets, and other high heat flux devices typically require heat sinks

Heat, Total (Enthalpy)

A thermodynamic quantity equal to the sum of the internal energy of a system plus the product of the pressure-volume work done on the system: h = E + pv where h = enthalpy or total heat content, E = internal energy of the system, p = pressure, and v =volume. For the purposes here, h = sensible heat + latent heat. Sensible heat is heat that causes a change in temperature. Latent heat is the change of enthalpy during a change of state


High-efficiency particulate air

High-efficiency Particulate Air (HEPA) Filters

These filters are designed to remove 99.97% or more of all airborne pollutants 0.3 microns or larger from the air that passes through the filter. There are different levels of cleanliness, and some HEPA filters are designed for even higher removal efficiencies and/or removal of smaller particles

High-performance Computing and Communications (HPCC)

Includes scientific workstations, supercomputer systems, high speed networks, special purpose and experimental systems, the new generation of large-scale parallel systems, and application and systems software with all components well integrated and linked over a high speed network

High-performance Group (HPG)

One of several groups within the SPEC organization. HPG has created the benchmark suite SPEChpc96, aiming at high-end machines including both shared-memory and distributed-memory architectures

High-performance Steering Committee (HPSC)

Executive group within HPG. Currently, HPG and HPSC are the same (i.e., all HPG members are part of HPSC)

Horizontal Displacement (HDP)

An air distribution system used predominantly in telecommunications central offices in Europe and Asia. Typically, this system introduces air horizontally from one end of a cold aisle

Horizontal Overhead (HOH)

An air distribution system that is used by some long-distance carriers in North America. This system introduces the supply air horizontally above the cold aisles and is generally utilized in raised-floor environments where the raised floor is used for cabling

Hot Aisle/Cold Aisle (from ASHRAE)

A common means of providing cooling to data communications rooms in which IT equipment is arranged in rows and cold supply air is supplied to the cold aisle, pulled through the inlets of the IT equipment, and exhausted to a hot aisle to minimize recirculation of the hot exhaust air with the cold supply air

Hot Aisle/Cold Aisle (from ASHRAE, industry)

* A common arrangement for the perforated tiles and the data communications equipment. Supply air is introduced into a region called the cold aisle
* On each side of the cold aisle, equipment racks are placed with their intake sides facing the cold aisle. A hot aisle is the region between the backs of two rows of racks
* The cooling air delivered is drawn into the intake side of the racks. This air heats up inside the racks and is exhausted from the back of the racks into the hot aisle

Hot Gas

Pressurized gas leaving the compressor (discharge) prior to entering the condensing surface


High-performance computing


The process of adding moisture to air or gases


Water vapor within a given space
* Absolute humidity: The mass of water vapor in a specific volume of a mixture of water vapor and dry air.
* Relative Humidity: Ratio of the partial pressure or density of water vapor to the saturation pressure or density, respectively, at the same dry-bulb temperature and barometric pressure of the ambient air. Ratio of the mole fraction of water vapor to the mole fraction of water vapor saturated at the same temperature and barometric pressure. At 100% relative humidity, the dry-bulb, wet-bulb, and dew-point temperatures are equal

Humidity Ratio

The ratio of the mass of water to the total mass of a moist air sample. It is usually expressed as grams of water per kilogram of dry air (gw/kgda) or as pounds of water per pound of dry air (lbw/lbda)

Humidity, Relative

See relative humidity

HVAC System Efficiency

See efficiency, HVAC system

Hydrofluorocarbon (HFC)

A halocarbon that contains only fluorine, carbon, and hydrogen


A term pertaining to water used for heating or cooling systems

Hygroscopic Dust Failure (HDF)

Sulfate and nitrate salts to which water adheres and promotes corrosion

HyperText Transmission Protocol (HTTP)

The protocol over TCP/IP by which the worldwide web communicates. The specifications for HTTP are available from the World Wide Web Consortium, which develops such standards


Formerly, the Institute of Electrical and Electronics Engineers, Inc.


Flow of outdoor air into a building through cracks and other unintentional openings and through the normal use of exterior doors for entrance and egress. Also known as air leakage into a building


A class of arithmetic, commonly used in computers. Integer arithmetic deals only in whole numbers, e.g., 1, 2, 99, 4563. Any calculation that does not result in a nice whole number is truncated back to a nice whole number and the fractional part is thrown away, e.g., 9/4 = 2 and not 2.25 or two and a quarter. Typically, computers can perform integer arithmetic more quickly than they can any other form of arithmetic, so most programs do as much work as they can in integer. However, most computers have significant limits on the values they can manage in integer format. Besides the lack of fractions, many computers cannot handle integer values beyond the millions. Thus, integers can be used to count time or to keep track of all the pennies in your bank account. However, most scientific applications deal with large values or need to be more precise than just throwing away the fractions. These kind of applications then make use of floating point arithmetic. For the SPEC CPU benchmarks, applications are classified as "integer" if they spend less than 1% of their time performing floating point calculations (which covers most non-scientific applications, e.g., compilers, utilities, simulators, etc.

International Electrotechnical Commission (IEC)

A global organization that prepares and publishes international standards for all electrical, electronic, and related technologies

Iron Whiskers

See whiskers, iron


International Organization for Standardization


Information technology


Information technology equipment


International technology roadmap for semiconductors

Keyboard-video-mouse (KVM) Switch

A piece of hardware that connects two or more computers to a single keyboard, monitor, and mouse


Link aggregation control protocol


The name of a performance group that originated the benchmark that came to be known as SPEC SFS. The name is an acronym of the companies from the original members: Legato, Auspex, Data General, Digital, Interphase, and Sun Microsystems


Link aggregation group identifier

Latent Heat Load

See heat load, latent

Leakage Airflow

Any airflow that does not flow along an intended path. Leakage airflow results in excess fan energy and may also result in higher energy consumption of refrigeration equipment

Leakage Current

Refers to the small amount of current that flows (or "leaks") from an output device in the off state caused by semiconductor characteristics


In computer terms, a library is a collection of sub-routines provided by the operating system or development environment that can be used to perform certain common tasks, e.g., read something off of disk, create a window on the display, sort an array of values, calculate the cosine of a value, etc.

License Agreement

An agreement that each licensee accepts prior to use of a product. In the SPEC case, this agreement covers what can and cannot be done with the SPEC benchmarks. Usually stating that any public use of any SPEC metrics must come from tests that were in complete agreement with the run and reporting rules for that benchmark


The transmission path between any two interfaces of generic cabling (from ISO/IEC 11801)

Link Aggregation Group (LAG)

A group of links that appear to a MAC client as if they were a single link. All links in a link aggregation group connect between the same pair of aggregation aystems. One or more conversations may be associated with each link that is part of a link aggregation group (see IEEE 802.3, Clause 43)

Link Partner

The device at the opposite end of a link segment from the local station. The link partner device may be either a DTE or a repeater (see IEEE 802.3, Clause 28)

Liquid Cooling

See cooling, liquid

Liquid- and Air-cooled Data Center

See data center, liquid- and air-cooled

Liquid-cooled Data Center

See data center, liquid-cooled

Liquid-cooled Electronics

See electronics, liquid-cooled

Liquid-cooled Rack

See rack, liquid-cooled

Liquid-cooled Server

See server, liquid-cooled

Liquid-cooled System

Conditioned liquid (e.g., water, etc., usually above dew point) is channeled to the actual heat-producing electronic equipment components and used to transport heat from that component where it is rejected via a heat exchanger (air to liquid or liquid to liquid) or extended to the cooling terminal device outside of the rack


Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, which maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose (NFPA 2002e)

Load Generator

Something that provides part of a workload to a SUT for a benchmark. Commonly in SPEC usage, this term applies to a client system that is used to drive the SUT over a LAN. However, this term can also be used to describe a process (either on a client or the SUT) which is generating a load for the benchmark

Load Level

For any benchmark which submits various amounts of work to a SUT, a load level is one such amount of work. This is usually in terms of expected throughput, such as "a load level of 100 operations per second was tried, but the SUT was not able to keep up and was only able to complete 80"

Local Area Network (LAN)

A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and/or radio waves. A system of LANs connected in this way is called a wide area network (WAN)


A high-performance computer made for high-volume, processor-intensive computing. This term is used for the processor unit, including main storage, execution circuitry, and peripheral units, usually in a computer center, with extensive capabilities and resources to which other computers may be connected so they can share facilities

Management Information Base (MIB)

A repository of information to describe the operation of a specific network device


Heat release rate in units of 1000 British thermal units (BTU) per hour

Mean Time to Repair (or Recover) (MTTR)

The expected time to recover a system from a failure, usually measured in hours

Measured Power

The heat release in watts

Media Access Control (MAC)

The data link sub-layer that is responsible for transferring data to and from the physical layer


Internal storage areas in the computer. The term memory identifies data storage that comes in the form of silicon, and the word storage is used for memory that exists on tapes or disks. The term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk


The final results of a benchmark. The significant statistics reported from a benchmark run. Each benchmark defines what are valid metrics for that particular benchmark


A chip that contains a CPU. The terms microprocessor and CPU are quite often used interchangeably


Provides a fault-tolerant connection from the blade server to the server chassis and other components. The midplane replaces an average of nine cables typically required in rack and pedestal server configurations, eliminating excessive cables

Minimum Efficiency Reporting Value (MERV)

Previously there were several specifications used to determine filter efficiency and characteristics. ASHRAE has developed the MERV categories so that a single number can be used to select and specify filters


Multimode fiber


The main circuit board of a computer. The motherboard contains the CPU, BIOS, memory, input/output ports, expansion slots, connectors for attaching additional boards and peripherals, and the controllers required to control those devices


Mean time between failure

Nameplate Rating

Equipment shall be provided with a power rating marking, the purpose of which is to specify a supply of correct voltage and frequency, and of adequate current-carrying capacity (IEC 60950, Clause 1.7.1)

Natural Convection Overhead (NOH)

An air distribution and cooling strategy in which cooling coils are suspended from the ceiling and air is circulated by natural convection with no fans or ducting


Formerly network equipment-building system. Provides a set of physical, environmental, and electrical requirements for a central office (CO) of a local exchange carrier (LEC). NEBS is a trademark of Telcordia Technologies, Inc.


National Electric Code


National Fire Protection Association


National Institute for Occupational Safety and Health

Non-raised Floor

Facilities without a raised floor utilize overhead ducted supply air to cool equipment. Ducted overhead supply systems are typically limited to a cooling capacity of 100 W/ft2 (Telcordia 2001)

Object Code

Object code is commonly the product of running source code through a compiler. It is usually a binary representation of the program statements translated into a form that is understood natively by the processor

Open Systems Group (OSG)

Within SPEC, this group works on benchmarks for evaluating the performance of systems running open (or publicly defined) operating systems (e.g., UNIX and its derivations, as well as NT and VMS)

Open Systems Steering Committee (OSSC)

Executive decision-making body within the Open Systems Group

Operating System

Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices, such as disk drives and printers. It ensures that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system. Operating systems provide a software platform on top of which other programs, called application programs, run

Operations, Administration, and Maintenance (OAM)

A group of network support functions that monitor and sustain segment operation, activities that are concerned with, but not limited to, failure detection, notification, location, and repairs that are intended to eliminate faults and keep a segment in an operational state and support activities required to provide the services of a subscriber access network to users/subscribers


Been specified by the benchmark standard

Optical Fiber

A filament-shaped optical waveguide made of dielectric materials

Original Design Manufacturer (ODM)

A company that designs equipment that is then marketed and sold to other companies under their own names, e.g., many IT equipment ODMs design and build servers in Taiwan and China

Original Equipment Manufacturer (OEM)

A company that manufactures equipment that is then marketed and sold to other companies under their own names


Occupational Safety and Health Administration

Owner's Program

A document that captures the facility's intent (mission) and performance requirements. ASHRAE Guideline 1-1996 states it is "the document that outlines the owner's overall vision for the facility and expectations of how it will be used and operated"


The property of a computer program, or program segment, that allows for the parallel execution of parts of the same program. Parallel programming covers a wide range of degrees, from the very small grain (e.g., similar operations on multiple elements of the same array or matrix) to large grain (e.g., simultaneous execution of unrelated procedures)

Pascal (PA)

A unit of pressure equal to one newton per square meter. As a unit of sound pressure, one pascal corresponds to a sound pressure level of 94

Patch Cord

Flexible cable unit or element with connector(s) used to establish connections on a patch panel (from ISO/IEC 11801: 1995)

Patch Panel

A cross-connect designed to accommodate the use of patch cords. It facilitates administration for moves and changes (from ISO/IEC 11801: 1995)


A mechanism for full duplex flow control (see IEEE 802.3, Annex 3_1B)


For SPEC's purposes, a peak configuration is one where the configuration is tuned especially to get the best result for a single, specific workload. Typically, this demonstrates the highest performance levels achievable. Peak is often used in combination with baseline configurations

Perforated Floor Tile

A tile as part of a raised-floor system that is engineered to provide airflow from the cavity underneath the floor to the space. Tiles may be with or without volume dampers

Performance Neutral

Performance neutral means that there is no significant difference in performance. For example, a performance neutral source code change would be one which would not have any significant impact on the performance as measured by the benchmark

Personal Digital Assistant (PDA)

A hand-held computer or personal organizer device

Physical Layer Entity (PHY)

Within IEEE 802.3, the portion of the physical layer between the medium mependent interface (MDI) and the media independent interface (MII), gigabit media independent interface (GMII), or 10 gigabit media independent interface (XGMII) consisting of the physical coding sublayer (PCS), the physical medium attachment (PMA), and if present, the WAN interface sublayer (WIS) and physical medium dependent (PMD) sublayers. The PHY contains the functions that transmit, receive, and manage the encoded signals that are impressed on and recovered from the physical medium (for example, see IEEE 802.3, Clauses 23-26, Clause 32, Clause 36, Clause 40, Clauses 48-54, Clauses 58-63, Clause 65, and Clause 66)


A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system (NFPA definition)

Point of Presence (PoP)

A place where communication services are available to subscribers. Internet service providers have one or more PoPs within their service area that local users dial into. This may be co-located at a carrier's central office


Portability flags or changes are those which are necessary for the correct execution of a benchmark. That is, the benchmark will not run or will produce the wrong output without these flags or changes


In computer terms, portable means that the code in question can be easily taken to a different system and made to work there. Code that is dependant upon quirks or specific resources of a certain system is usually considered not to be portable because of the difficulties in finding means of supporting these dependencies on the new system. The use of standardized definitions and interfaces, e.g., ANSI-C and POSIX, greatly aids portability because the difficult dependencies are hidden behind the standardized interfaces and the difficulties are shifted from the programmer to the system provider


Time rate of doing work usually expressed in horsepower or watts

Power Bus (or Electrical Bus)

See bus, power

Power Distribution Unit (PDU)

The junction point between the UPS and the cabinets containing equipment

Power Usage Effectiveness (PUE)

Globally accepted metric that is described by The Green Grid in several whitepapers. PUE illustrates the total energy used by a data center divided by the energy used by ICT equipment in that data center

Printed Circuit Board (PCB)

Board that contains layers of circuitry used for interconnecting the other components


See central processing unit (CPU)

Psychrometric Chart

A graph of the properties (temperature, relative humidity, etc.) of air. It is used to determine how these properties vary as the amount of moisture (water vapor) in the air changes


Machine for imparting energy to a fluid, causing it to do work
* Centrifugal pump: Pump having a stationary element (casing) and a rotary element (impeller) fitted with vanes or blades arranged in a circular pattern around an inlet opening at the center. The casing surrounds the impeller and usually has the form of a scroll or volute
* Diaphragm pump: Type of pump in which water is drawn in and forced out of one or more chambers by a flexible diaphragm. Check valves let water into and out of each chamber
* Positive displacement pump: Has an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. Examples of positive displacement pumps include reciprocating pumps and rotary pumps
* Reciprocating pump: A back-and-forth motion of pistons inside of cylinders provides the flow of fluid. Reciprocating pumps, like rotary pumps, operate on the positive principle. That is each stroke delivers a definite volume of liquid to the system
* Rotary pump: Pumps that deliver a constant volume of liquid regardless of the pressure they encounter. A constant volume is pumped with each rotation of the shaft and this type of pump is frequently used as a priming pump

Rack (from ASHRAE)

Frame for housing electronic equipment

Rack (from ASHRAE, industry)

Structure for housing electronic equipment. Differing definitions exist between the computing industry and the telecommunications industry
* Computing industry: A rack is an enclosed cabinet housing computer equipment. The front and back panels may be solid, perforated, or open depending on the cooling requirements of the equipment within
* Telecommunications industry: A rack is a framework consisting of two vertical posts mounted to the floor and a series of open shelves upon which electronic equipment is placed. Typically, there are no enclosed panels on any side of the rack

Rack Power

Used to denote the total amount of electrical power being delivered to electronic equipment within a given rack. Often expressed in kilowatts (kW), this is often incorrectly equated to be the heat dissipation from the electrical components of the rack

Rack, Air- and Liquid-cooled

Rack that requires both air and liquid provided by the building

Rack, Air-cooled

System conditioned by removal of heat only using air

Rack, Liquid-cooled

A liquid-cooled rack that accepts conditioned coolant; system conditioned by removal of heat using a liquid

Rack-mounted Equipment

Equipment that is to be mounted in an EIA (Electronic Industry Alliance) or similar cabinet. These systems are generally specified in EIA units, such as 1U, 2U, 3U, etc., where 1U = 1.75 inches (44 mm)

Raised Floor (from ASHRAE)

A platform with removable panels where equipment is installed with the intervening space between it and the main building floor used to house the interconnecting cables, which at times is used as a means for supplying conditioned air to the information technology equipment and the room

Raised Floor (from ASHRAE, industry)

Also known as access floor. Raised floors are a building system that utilizes pedestals and floor panels to create a cavity between the building floor slab and the finished floor where equipment and furnishings are located. The cavity can be used as an air distribution plenum to provide conditioned air throughout the raised floor area. The cavity can also be used for routing of power/data cabling infrastructure

Random Access Memory (RAM)

A configuration of memory cells that hold data for processing by a computer's processor. The term random derives from the fact that the processor can retrieve data from any individual location, or address, within RAM

Rated Current

The rated current is the absolute maximum current that is required by the unit from an electrical branch circuit

Rated Frequency

The supply frequency as declared by the manufacturer

Rated Frequency Range

The supply frequency range as declared by the manufacturer expressed by its lower and upper rated frequencies

Rated Voltage

The supply voltage as declared by the manufacturer

Rated Voltage Range

The supply voltage range as declared by the manufacturer


Room-cooling class

Redundancy (from ASHRAE)

"N" represents the number of pieces to satisfy the normal conditions. Redundancy is often expressed compared to the baseline of "N." Some examples are "N+1," "N+2," "2N," and 2(N+1). A critical decision is whether "N" should represent just normal conditions or whether "N" includes full capacity during off-line routine maintenance. Facility redundancy can apply to an entire site (backup site), systems, or components. IT redundancy can apply to hardware and software

Reference Time

The amount of time that a particular benchmark took to run on a specific reference platform


In a refrigerating system, the medium of heat transfer that picks up heat by evaporating at a low temperature and pressure and gives up heat on condensing at a higher temperature and pressure

Relative Humidity (RH)

* Ratio of the partial pressure or density of water vapor to the saturation pressure or density, respectively, at the same dry-bulb temperature and barometric pressure of the ambient air
* Ratio of the mole fraction of water vapor to the mole fraction of water vapor saturated at the same temperature and barometric pressure at 100% relative humidity, the dry-bulb, wet-bulb, and dew-point temperatures are equal

Releasing Panel

A particular fire alarm control panel whose specific purpose is to monitor fire detection devices in a given area protected by a suppression system and, upon receiving alarm signals from those devices, actuate the suppression system

Reliability (from ASHRAE)

A percentage value representing the probability that a piece of equipment or system will be operable throughout its mission duration. Values of 99.9% (three 9s) and higher are common in data and communications equipment areas. For individual components, the reliability is often determined through testing. For assemblies and systems, reliability is often the result of a mathematical evaluation based on the reliability of individual components and any redundancy or diversity that may be employed

Reliability (from ASHRAE, industry)

Reliability is a percentage value representing the probability that a piece of equipment or system will be operable throughout its mission duration. Values of 99.9 percent (three 9s) and higher are common in data and communications equipment areas. For individual components, the reliability is often determined through testing. For assemblies and systems, reliability is often the result of a mathematical evaluation based on the reliability of individual components and any redundancy or diversity that may be employed

Remote Power Panel (RPP)

A term typically used to describe electrical panels outside of electrical equipment rooms

Reporting Rules

The set of benchmark rules that defines what constitutes a valid full disclosure for that benchmark. Usually these define what parts of the benchmark configuration and the system configuration(s) that need to be detailed and disclosed

Response Time

The amount of time from when an action is requested until the time that the request completes and is returned to the requestor


The value of the primary metric being reported for the benchmark

Return Air (RA)

See air, return


Return Heat Index


A vertical pipe in a building

Room Load Capacity

The point at which the equipment heat load in the room no longer allows the equipment to run within the specified temperature requirements of the equipment. The load capacity is influenced by many factors. The primary one is the room's theoretical capacity. Other factors, such as the layout of the room and load distribution, also influence the room load capacity

Room Theoretical Capacity

The capacity of the room based on the mechanical room equipment capacity. This is the sensible tonnage of the mechanical room for supporting the computer or telecommunications room heat loads

Rotary Heat Exchanger

See exchanger, rotary heat

Rotary UPS

See UPS, rotary


A layer 3 interconnection device that appears as a media access control (MAC) to a CSMA/CD collision domain (see IEEE Std 610.7-1995 [B38])

Run Rules

The set of benchmark rules that defines what constitutes a valid test with that benchmark. Usually these define legal configurations, experimental limitations, and any operating constraints


A file that contains a sequence of instructions for an interpreter or the script for that interpreter to follow


A material that is neither a good conductor of electricity nor a good insulator. The most common semiconductor materials are silicon, gallium arsenide, and germanium. These materials are then doped to create an excess or lack of electrons and used to build computer chips

Sensible Heat Load

See heat load, sensible

Sensible Heat Ratio (SHR)

Ratio of the sensible heat load to the total heat load (sensible plus latent)


A computer that provides some service for other computers connected to it via a network. The most common example is a file server, which has a local disk and services requests from remote clients to read and write files on that disk

Server, Air- and Liquid-cooled

Server that requires both air and liquid provided by the building

Server, Air_cooled

An air-cooled server that accepts only room air

Server, Liquid-cooled

A liquid-cooled server that accepts conditioned coolant

Service Level Agreement (SLA)

A contract between a network service provider and a customer that specifies, usually in measurable terms, what services the network service provider will furnish


Known as SPEC SFS, SFS93 is the NFS server benchmark which evolved from LADDIS


SPEC SFS97 is the NFS server benchmark which replaced SFS93


SFS97_R1 is version 3 of the NFS benchmark, replacing the SFS97 suite


A UNIX term for a command interpreter and its environment. Typically a program that supports the interpretation and execution of commands

Shielded Twisted-pair (STP) Cable

An electrically conducting cable, comprising one or more elements, each of which is individually shielded. There may be an overall shield, in which case the cable is referred to as shielded twisted-pair cable with an overall shield (from ISO/IEC 11801: 1995). Specifically for IEEE 802.3 100BASE-TX, 150 O balanced inside cable with performance characteristics specified to 100 MHz (i.e., performance to Class D link standards as per ISO/IEC 11801: 1995). In addition to the requirements specified in ISO/IEC 11801: 1995, IEEE Std 802.3, Clause 23 and Clause 25, provide additional performance requirements for 100BASE-T operation over STP


Sensible heat ratio

Simplex Fiber Optic Link Segment

A single fiber path between two medium attachment units (MAUs) or PHYs, including the terminating connectors, consisting of one or more fibers joined serially with appropriate connection devices, i.e., patch cables and wall plates (see IEEE 802.3, Clause 15)

Single Precision

A level of floating point accuracy that usually requires half the space for each value than does double precision, but provides considerably less precision. For most systems running the SPEC CPU tests from the OSG (e.g., CPU95), single precision implies a 32-bit value

Single-point Failure

Any component that has the capability of causing failure of a system or a portion of a system if it becomes inoperable


Service level agreement


Single-mode fiber


Signal-to-noise ratio

Sound Transmission Class (STC)

This is an acoustical rating for the reduction in sound of an assembly. It is typically used to denote the sound attenuation properties of building elements, such as walls, floors, and ceilings. The higher the STC, the better the sound-reducing performance of the element

Source Code

The human readable form of a computer program. This is typically the form in which the program is written, read, and modified by its human author(s)


A common (mis)name for the CPU95 benchmarks. Also, SPEC89 implies CPU89, SPEC92 should be CPU92, and SPEC2000 is CPU2000


Official name of the Gamess application of SPEChpc96, an application representative of computations used by the chemical industry


The first benchmark suite released by SPEC/HPG, and it includes the two applications Seismic and Gamess


SPECjvm98 is the current Java Virtual Machine benchmark suite from SPEC


SPECmarks were the metrics for SPEC's original CPU89 benchmarks. Now, the term is often used to refer collectively to the CPU95 ratio speed metrics


A throughput metric based on the SPEC CPU benchmarks, such as SPEC CPU95. This metric measures a system's capacity for processing jobs of a specified type in a given amount of time. The metric is used the same for multi-processor systems and for uniprocessors. It is not necessarily a measure of how fast a processor might be, but rather a measure of how much work the one or more processors can accomplish. SPECrates are one style of metric from the SPEC CPU benchmarks, the other are SPECratios


A measure of how fast a given system might be. It is calculated by taking the elapsed time that was measured for a system to complete a specified job and dividing that into the reference time (the elapsed time that job took on a standardized reference machine). This measures how quickly, or more specifically, how many times faster than a particular reference machine, one system can perform a specified task. SPECratios are one style of metric from the SPEC CPU benchmarks, the other are SPECrates


Official name of the Seismic application of SPEChpc96. It is an application representative of computations used by the seismic industry


SPECweb2005 is a standardized performance test for WWW servers, the successor to SPECweb99 and SPECweb99_SSL. The benchmark consists of different workloads (both SSL and non-SSL), such as banking and e-commerce, and writes dynamic content in scripting languages to more closely model real-world deployments. The web server also communicates with a lightweight backend to simulate an application/database server


SPECweb96 is SPEC's first attempt at a benchmark for WWW servers. It measures a server's ability to handle HTTP/1.0 GET requests from a number of external client drivers


SPECweb99 is one of the current web server benchmarks, which replaced the SPECweb96 product


For the OSG, the entity that has accepted the license agreement. In other words, the people who are responsible for ensuring that the results were obtained in accordance with any existing run and reporting rules. For the HPG, See benchmark sponsor who is a technical advisor for a particular benchmark

Standard Performance Evaluation Corporation (SPEC)

An organization of computer industry vendors dedicated to developing standardized benchmarks and publishing reviewed results

Static RAM (SRAM)

Random access memory (RAM) that retains data bits in its memory as long as power is being supplied. SRAM provides faster access to data and is typically used for a computer's cache memory

Static UPS

See UPS, static

Steering Committee

Part of the SPEC bureaucracy. Each free-standing group within SPEC has a steering committee that acts as the key decision-making body with full membership votes typically being reserved for benchmark ratifications and elections

Supply Air

See air, supply


A layer 2 interconnection device that conforms to the ISO/IEC 10038 [ANSI/IEEE 802.1D-1998]


Combination of electrical disconnects and/or circuit breakers meant to isolate equipment in or near an electrical substation

Symbol Rate (SR)

Within IEEE 802.3, the total number of symbols per second transferred to or from the medium dependent interface (MDI) on a single wire pair. For 100BASE-T4, the symbol rate is 25 MBd. For 100BASE-X, the symbol rate is 125 MBd. For 100BASE-T2, the symbol rate is 25 MBd. For 1000BASE-T, the symbol rate is 125 MBd

System Under Test (SUT)

The system being tested, as distinct from anything in the testbed being used to drive the test

System, Air Cooled

Conditioned air is supplied to the inlets of the rack/cabinet 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 terminal cooling device outside of the rack is air


A networking protocol developed for the creation of a robust internet being a connection across a variety of local networking mechanisms. The protocol used to connect to and through what is known today as the internet. The internet uses a layered architecture with several protocols. The TCP (Transmission Control Protocol) defines session-based communications, and the IP (Internet Protocol) addresses the lower-level issues of packet fragmentation and routing


Time domain reflectometer




The degree or intensity of heat present in a substance or object

Temperature, Dew-point

The temperature at which water vapor has reached the saturation point (100% relative humidity)

Temperature, Dry-bulb

Temperature of air indicated by an ordinary thermometer

Temperature, Wet-bulb

The temperature indicated by a psychrometer when the bulb of one thermometer is covered with a water-saturated wick over which air is caused to flow at approximately 4.5 m/s (900 ft/min) to reach an equilibrium temperature of water evaporating into air, where the heat of vaporization is supplied by the sensible heat of the air


The entire test setup, including the SUT and any external systems used to drive, coordinate, or monitor the benchmark

Thermal Effectiveness

Measure of the amount of mixing between hot and cold airstreams before the supply air can enter the equipment and before the equipment discharge air can return to the air-handling unit

Thermal Efficiency

Energy output as a percentage of energy input of a machine or process

Thermal Storage Tank

Container used for the storage of thermal energy. Thermal storage systems are often used as a component of chilled-water systems


An arrangement of tubes for assisting circulation in a liquid through the use of capillary action


Telecommunications Industry Association

Tin Whiskers

See whiskers, tin


The unit of measure used in air conditioning to describe the heating or cooling capacity of a system. One ton of heat represents the amount of heat needed to melt one ton (2,000 lb) of ice in one hour. 12,000 Btu/h equals one ton of heat

Total Heat (Enthalpy)

See heat, total

Turn-down Ratio

Ratio representing highest and lowest effective system capacity. Calculated by dividing the maximum system output by the minimum output at which steady output can be maintained. For example, a 3:1 turn-down ratio indicates that minimum operating capacity is one-third of the maximum

Twisted Pair

A cable element that consists of two insulated conductors twisted together in a regular fashion to form a balanced transmission line (from ISO/IEC 11801: 1995)

Twisted-pair Cable

A bundle of multiple twisted pairs within a single protective sheath (from ISO/IEC 11801: 1995)

Unshielded Twisted-pair Cable (UTP)

An electrically conducting cable, comprising one or more pairs, none of which is shielded. There may be an overall shield, in which case the cable is referred to as unshielded twisted-pair with overall shield (from ISO/IEC 11801: 1995)


A type of air conditioning system that discharges air upward into an overhead duct system


Uninterruptible power supply

UPS, Rotary

A flywheel-driven UPS that is used for applications requiring ride-through of short-duration power system outages, voltage dips, etc. The flywheel-driven rotary UPS typically does not include batteries, and support times are usually on the order of a few seconds to a few minutes

UPS, Static

Typically uses batteries as an emergency power source to provide power to data communications facilities until emergency generators come on line


* The time during which a computer is operational. Downtime is the time when it isn't operational
* Sometimes measured in terms of a percentile. For example, one standard for uptime that is sometimes discussed is a goal called five 9s, which is a computer that is operational 99.999 percent of the time

Utility Computing

The vision of utility computing is to access information services in a fashion similar to those provided by telephone, cable TV, or electric utilities. It is a service provisioning model in which a service provider makes computing resources and infrastructure management available to the customer as needed and charges them for specific usage rather than a flat rate. Like other types of ondemand computing, such as grid computing, the utility model seeks to maximize the efficient use of resources and/or minimize associated costs


A device to stop or regulate the flow of fluid in a pipe or a duct by throttling

Vapor Barrier

A material or construction that adequately impedes the transmission of water vapor under specified conditions

Variable Frequency Drive (VFD)

A system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor

Variable Speed Drive (VSD)

A system for controlling the rotational speed of either an alternating current (AC) or direct current (DC) motor by varying the voltage to the electrical power supplied to the motor


Variable air volume


The property of a computer program, or program segment, that allows for the simultaneous execution of operations on different data values, thus making it possible to allocate the work to a set of operators and accomplish the work in parallel. One example of work that is very vectorizable is taking an entire matrix of values and multiplying each by 2. It is possible for different operators to work on different cells of the matrix at the same time. One example of work that is not vectorizable is adding to each item in an array the value of the preceding item in the array as each calculation is dependent upon the results of the preceding calculation so there is no way to perform the operations at the same time. Vectorization is only one sub-class - probably one of the most restrictive sub-classes - of parallelizable programming


* Vector Quantity: Denotes the simultaneous time rate of distance moved and the direction of a linear motion
* Face Velocity: Velocity obtained by dividing the volumetric flow rate by the component face area


The process of supplying or removing air by natural or mechanical means to or from any space. Such air may or may not have been conditioned

Vertical Overhead (VOH) Class

Refers to the delivery of air from overhead ductwork

Vertical Underfloor (VUF) Class

Refers to the delivery of air from an underfloor space, i.e., a raised-floor cavity


Common alternative to logical, often used to refer to the artificial objects (such as addressable virtual memory larger than physical memory) created by a computer system to help the system control access to shared resources

Virtual Machine (VM)

A self-contained operating environment that behaves as if it is a separate computer. For example, Java applets run in a Java virtual machine that has no access to the host operating system. This design has two advantages:
* System Independence: An application will run the same in any VM regardless of the hardware and software underlying the system
* Security: Because the VM has no contact with the operating system, there is little possibility of a program damaging other files or applications. The second advantage, however, has a downside. Because programs running in a VM are separate from the operating system, they cannot take advantage of special operating system features

Virtual Private Network (VPN)

The use of encryption in the lower protocol layers to provide a secure connection through an otherwise insecure network, typically the internet. VPNs are generally cheaper than real private networks using private lines but rely on having the same encryption system at both ends. The encryption may be performed by firewall software or possibly by routers

Virtual Server

* A configuration of a networked server that appears to clients as an independent server but is actually running on a computer that is shared by any number of other virtual servers. Each virtual server can be configured as an independent website with its own hostname, content, and security settings
* Virtual servers allow internet service providers to share one computer between multiple websites while allowing the owner of each website to use and administer the server as though they had complete control

VLA Battery

See battery, VLA


Virtual Bridged Local Area Network (see IEEE P802.1Q)

Volatile Organic Compounds (VOCs)

Organic (carbon-containing) compounds that evaporate readily at room temperature. These compounds are used as solvents, degreasers, paints, thinners, and fuels

VRLA Battery

See battery, VRLA


Any thin but rigid plate of solid material, especially of disk shape. A term used commonly to refer to the thin slices of silicon used as starting material for the manufacture of integrated circuits

Warm Up

A period of time prior to when the actual measurement is taken, where the workload has been already started in an effort to get the SUT to a stable and consistent state

Water Economizer

See economizer, water

Wet-bulb Temperature

See temperature, wet-bulb

Whiskers, Iron

Crystalline metallurgical phenomenon whereby iron grows tiny hairs, which can become airborne under certain conditions and settle in electronic equipment

Whiskers, Tin

A crystalline metallurgical phenomenon whereby tin grows tiny hairs, which can become airborne under certain conditions and settle in electronic equipment

Whiskers, Zinc

A crystalline metallurgical phenomenon whereby zinc grows tiny hairs, which can become airborne under certain conditions and settle in electronic equipment


The units of work that are to be performed during a benchmark run

Zinc Whiskers

See whiskers, zinc